Monday, July 13, 2015

Diabetes Mellitus by Germaine Hung and Kate Wood April 1, 2010



Diabetes Mellitus  
Introduction
Diabetes mellitus is a relatively common disease in our companion animals.  Dogs typically have decreased insulin production and are dependent on insulin to manage the disease.  Diet may play a role in management as often these dogs are overweight.  In dogs, weight loss, complex carbohydrates, and fibre in the diet can help manage diabetes mellitus. Cats, however, tend to have a problem with insulin resistance, not insulin production, because of being overweight. One theory is the high processed carbohydrate content in most commercial dry diets may be contributing to obesity and  the development of diabetes mellitus; thus, a diet low in simple sugars and higher in protein may be beneficial.
               In recent years, the human-animal bond has become very important.  People are treating their pets as part of the family and providing them with the best possible care has become a priority.  Along with this trend, the pet nutrition industry has also been growing with diets specific to a life stage, health condition, and even breeds.  Due to increasing demand, the number of pet diets available has increased exponentially .  To a client, the number of food choices can be overwhelming.  In addition to the over the counter diets, some wellness and  therapeutic  diets are available only through a veterinarian.
The task given to us as veterinary students was to evaluate the prescription veterinary diets available for diabetes mellitus and choose a corresponding commercial diet to compare to that is available from a pet store that might be appropriate for a diabetic patient, which, generally resulted in choosing weight loss diets for dogs and kitten diets for the cats.

 

Methodology
To study and analyze the diets indicated for diabetes mellitus the dry veterinary therapeutic  diet formulas from the four major pet food companies (Purina, MediCal/Royal Canin, Hill’s, and Iams) and one of their corresponding over-the-counter (OTC) diets most appropriate for a diabetic patient.   were selected The veterinary canine diets selected were Purina’s DCO (PVD DCO), MediCal Fibre Formula, Hill’s Prescription diet w/d, and Iams Veterinary Diets Optimal Weight Control D (IVD Optimal Wt Ctrl D).  The corresponding OTC diets were Purina ProPlan Chicken and Rice Weight Management, Pedigree Healthy Weight Control, Hill’s Science Diet Adult Light, and Iams ProActive Health Weight Control respectively.  The veterinary feline diets selected were Purina veterinary diet DM (PVD DM), MediCal Diabetes DS, Hill’s Prescription diets w/d and m/d and Iams Veterinary Diets Optimal Weight Control D (IVD Optimal Wt Ctrl D).  The corresponding OTC feline diets were Purina ProPlan Weight Management, Royal Canin Kitten 36, Hill’s Science Diet Kitten Healthy Development and Iams ProActive Health Kitten (Table 1).


Using the company websites, consumer nutritional consultants, the bags of the food and specific brochures for each diet, we were able to obtain the majority of our guaranteed analysis, typical analysis, and ingredient lists for each diet.  The “as fed” values were all converted into g/1000 kcal as a common denominator to facilitate comparisons of the diets.  For each individual diet the guaranteed analysis was compared to the typical analysis to determine if they were similar.  Both the guaranteed and typical analyses were compared to the minimum standards; National Research Council (NRC) nutrient requirements set in 2006 for dogs and nutrient requirements based on a prey diet for cats.  The typical analysis (or guaranteed analysis in situations where information was lacking) of the veterinary diet was then compared to its OTC counterpart to determine the similarities and differences.  Finally the four prescription veterinary diets were compared to each other looking for similarities/differences and the ingredients of all diets were compared to each other to look at the different protein, carbohydrate, fibre, and fat sources.
               Daily maintenance energy requirements were calculated using the following formula: DER = [(body weight in kg x 30) + 70] x activity factor.  The maintenance activity factor was 1.8 for a dog and 1.2 for a cat.  The daily energy requirement (DER) was determined to be 666 kcal/day for a 10 kg dog in ideal body condition.  The DER for a 6 kg cat was determined to be 300 kcal/day.  The DER was compared to the kcal/day recommendation from the manufacturer based on the published feeding guide.  The cost to feed each diet was determined from the prices set at the Western College of Veterinary Medicine Veterinary Teaching Hospital for the prescription diets and prices at local pet stores in Saskatoon, Saskatchewan for the OTC diets.
Results
               The comparisons of the eight canine diets are summarized in Table 2.  Typically the manufacturer’s recommended caloric intake, based on the published feeding guide, was less than the DER of 666 kcal/day.  This is likely due to the majority of diets being marketed as a weight loss/weight control diet. 
Protein content in the eight diets ranged from 61 – 90 g/1000 kcal.  Overall the veterinary diets contained more protein than the associated OTC diet; the exception being Hill’s where their Science Diet Adult Light contains more protein than their w/d.  Fat ranged from 27-36 g/100 kcal with the majority of diets in the 32 ± 2 g/1000 kcal range.  Iams diets were lower in fat and the two diets with the highest fat content were ProPlan and MediCal Fibre.  No trend between the veterinary diets versus the OTC diets was noticed.  Carbohydrate content was not available for most diets.  Where available, the carbohydrate content was highly variable.  Fibre content was above the NRC minimal standards with the exception of the two Iams diets.  Hill’s and Purina separated their fibre content into insoluble and soluble fibre.  A ratio of insoluble to soluble fibre of 20:1 and 5:1 was present respectively.  Carnitine was listed as an ingredient in three of the four veterinary diets; Hill’s, Iams, and MediCal.  The values of carnitine were available for all but the latter diet.  There is no reference value set by NRC for carnitine requirements. 
               While comparing the ingredients it became quite obvious that the ingredients were more similar than different.  Most diets use chicken or chicken by-product meal as their main protein source.  Pedigree did not state what meat was in their meat and bone by-product meal.  Carbohydrate sources are mainly corn based but can occasionally be rice based.  Iams used grain and barley sorghum in both their veterinary and OTC diets.  Fibre was usually supplied in the form of beet pulp or soybean mill run.  PVD DCO had pea fibre, MediCal Fibre used rice hulls, Hill’s used powdered cellulose, and Iams had gum arabic in addition to beet pulp or soybean mill run.  The remainder of the ingredient lists were very similar in their added vitamin and mineral supplements.
               Cost per day to feed 666 kcal/day of each food was calculated based on prices from either the Western College of Veterinary Medicine’s teaching hospital or nearby Saskatoon pet stores.  Overall the veterinary prescription diets were more expensive than the over the counter diets, as expected.  PVD DCO is the most expensive to feed.  The other veterinary diets were quite comparable to each other (Table 3, Figure 1). 
With regards to the feline diets, the manufacturer’s daily recommended intake was generally more than the calculated intake for a 6 kg cat (Table 5 and figure 2).  The diet that had the closest recommendation to the 300 kcal/day was Hills W/D and the diet with the highest recommended intake was Science Diet Kitten Healthy Development.  The protein content of the diets ranged from 74-148 g/1000kcal, this range remains below that of the prey diet recommended protein intake despite the fact that almost all the prescription diets make the claim of containing high protein. The diets with the highest levels of protein were Hills M/D and Purina ProPlan Weight Management. Carbohydrate content of the diets ranged between 3.4-13.5 g/100kcal, again none of which were as low as the .5 g/100kcal in the prey diet even though the majority of the prescription diets broadcasted claims of low carbohydrate content.  The two diets with the lowest carbohydrate content were Purina DM and Hills M/D.  Fat ranged from 3.2-7.3 g/100kcal, the only diets that were elevated above the prey diet standard were Hills M/D and Science Diet Kitten Healthy Development.  Fibre ranged from .3-2.7 g/100kcal, with Hills W/D and Hills M/D being above the values presented in the prey diet.  The calcium to phosphorus ratios never exceeded the appropriate 1:1 or 2:1 ratios in any of the diets and both calcium and phosphorus ranged from .2-.4 g/100kcal, this range however, did not meet the values of the prey diet.  All of these findings are summarized in table 4.
When ingredient lists were compared, it was noted that all the companies use similar ingredients.  The major sources of carbohydrates in the ingredients were corn and rice, whereas, the main sources of protein were gluten meals or soy protein.  All diets start off with a base of chicken by-product meal, chicken or chicken meal. Hills M/D and W/D contained powdered cellulose as their fifth ingredient, which, coincides with them having the highest fibre content of all the diets compared.
The cost comparison was based on a 6 kg cat consuming 300kcal/day and the prices were obtained from the Western College of Veterinary Medicine and local pet food stores in Saskatoon, Saskatchewan.  Table 6 and figure 3 display the cost comparison, where the most expensive diet was MediCal and the least expensive diet was Iams ProActive Health Kitten.  As a general observation, the most expensive diets were generally the prescription diets (true for all diets except Hills W/D).
Discussion
               Recent work has mainly focused on the use of high fibre diets in the management of diabetes mellitus in dogs.  Graham et al. found that the control of diabetes improved in dogs when they were fed a high fibre diet resulting in reductions of mean plasma glucose concentrations, a smoother and less erratic blood glucose curve, and a decrease in postprandial glucose concentrations.  Markers of glycemic control, including plasma fructosamine, glycosylated hemoglobin, free glycerol, and cholesterol concentrations, were also improved.  Subjectively both the owner and the veterinarian noticed an improvement in patient demeanour and activity level on the high fibre diet.  These changes were still present at a four month follow up; however, weight loss was an effect of the long term feeding of a high fibre diet.  This study was more an observational study of a high fibre diet being fed long term.   They had a small sample size (n= 10), which may preclude being able to apply the results to a larger population.  Their test diet was a canned diet high in insoluble and soluble fibre and relatively low in fat, due to this, it is hard to determine if the results of this study were because of the high fibre alone or if the low fat content also played a role in the improvement of diabetic control.  The researchers did try and elicit objective and subjective measures of diabetic control.
               Another study, Kimmel et al.2, focused more on the effects of insoluble versus soluble fibre.  They found mean and maximum blood glucose concentrations and the area under the blood glucose curve was significantly lower in dogs fed the high insoluble fibre diet.  Fructosamine concentration was significantly lower in dogs fed either of the high fibre diets compared to the lower fibre diet but improvement in glycosylated hemoglobin was only seen when on the high insoluble fibre diet.  It appears the diets high in insoluble fibre may be more beneficial than those higher in soluble fibre.  This study was a randomized blinded crossover study.  It looked at three different diets; high insoluble fibre, high soluble fibre that contained both soluble and insoluble fibre, and low fibre.   Unfortunately the high soluble fibre diet also contained insoluble fibre which makes it more difficult to determine the source of the benefits.  Like the previous study1, the study population was small (n=7) but it was also a population of mixed breeds.  Another possible confounding factor in this study is the diets themselves, the source of carbohydrates were different in the diets.  The high insoluble fibre diet contained corn only whereas the high soluble fibre diet and the low fibre diet contained corn and rice.  Rice has been previously determined to have a higher postprandial glucose response than corn2.  Also left unanswered in this study was whether or not the source of insoluble fibre (eg. powdered cellulose versus peanut hulls) makes a difference in glycemic control.
               Even though many studies have shown benefits from a high fibre diet, this may not necessarily be true.  Recently Fleeman et al.3 published their study showing a lack of advantage of high fibre diets in dogs with stabilized diabetes.  They defined their study population as dogs in stable glycemic control if the following criteria were met in the two months prior to the beginning of the study: fluctuation of insulin dose by 1 unit or less, water drunk less than 70 ml/kg/day, stable body weight, and absence of ketones in the urine.  This crossover study was in a small population (n=12) of stable diabetic dogs.  The dogs were fed two diets with high fibre, moderate carbohydrates, and two levels of fat and compared to a commercial canned diet with moderate fibre, low carbohydrate, and higher fat.  The researchers found no significant differences in the insulin requirement or glycemic control as measured by fructosamine, glycosylated hemoglobin, and serial blood glucose measurements among the three diets.  The high fibre, moderate carbohydrate, moderate fat diet resulted in weight loss but also an improved lipid profile compared to the high fibre, moderate carbohydrate, high fat diet and the moderate fibre, low carbohydrate, high fat diet.  While they did not notice any direct benefits to diabetic management with the high fibre diets they did notice the improved lipid profile with the high fibre, moderate carbohydrate, moderate fat diet and proposed this composition of diet may be beneficial to diabetic dogs with persistent hypertriglyceridemia or recurrent pancreatitis.  However, if not required, the high fibre diet can result in a loss of body condition and may not be ideal for a stabilized diabetic patient.
               Based on the results of these three studies, arguments can be made for either a high fibre diet or a moderate fibre diet lower in carbohydrates to optimize dietary management of diabetes mellitus.  It appears that for diabetic patients, who are concurrently overweight, a high fibre diet, moderate carbohydrate, and low fat diet may be the most beneficial to initiate dietary management of diabetes.  This dietary composition will help the patient lose weight and since increased fat stores can result in insulin resistance, weight loss is beneficial for the diabetic patient.  Diets that contain carnitine may be most beneficial in obese diabetic dogs, as carnitine has been shown to enhance fat metabolism by increasing movement of fatty acids into the mitochondria for beta oxidation4.  Once an ideal body condition has been achieved dietary needs may change and at this point a diet with higher protein, moderate fibre, low to moderate carbohydrates, and low to moderate fat may be more appropriate.  In a small study of working dogs they found that high protein diets offered higher apparent nutrient digestibility, slower release of glucose into the bloodstream, and a reduction of large intestinal fermentation of carbohydrates5.  This type of diet has a lower glycemic index than those with more caloric energy coming from carbohydrates.
               The evidence suggested by these studies support the claims that the pet food companies are making regarding their diets indicated for diabetes (weight loss and higher fibre to improve glycemic control).   It appears the majority of the pet food companies are also including some level of carnitine into their diets to maximize the fat metabolism.  These diabetic diets are often focused mainly on weight loss, which is important in the initial stages but as demonstrated by Graham et al.1, Kimmel et al.2 and Fleeman et al.3, long term high fibre diets can result in significant weight loss.  Thus, maybe pet food companies should be considering changing their dietary strategy once the patient has reached an ideal body condition.
               After reviewing the literature and analyzing these diets, it is still difficult to state that one diet is better than another.  Another factor that has not been discussed is each individual dog’s response to a diet.  Like humans, each dog is unique and a diet that works for one dog may not work for another dog.  The advantage of having so many available diets is that it provides the opportunity to try different diets and find the one most appropriate for that specific animal.  However, if we were to make a recommendation for a prescription diet, Hill’s prescription diet may be the most appropriate because it contains the most carnitine of the diets analyzed, it meets the minimum standards set by the NRC, it contains a high ratio of insoluble to soluble fibre, and appears to be the most cost effective.  For clients who are unwilling to use a prescription veterinary diet for any number of reasons (eg. cost and inconvenience) then the Hill’s over the counter alternative, Science Diet Adult Light, may be an appropriate choice as the formulation appears to be similar to that of its prescription diet.
               With regards to feline research, the topics of low carbohydrate and high protein diets as well as fibre in feline diets has been researched and discussed.  There is currently a large trend towards feeding felines lower carbohydrate diets; this trend has probably occurred as people have started to acknowledge the fact that cats are evolutionary obligate carnivores and from suggestions that feeding of high carbohydrate diets has interfered with our ability to treat and cause remission of feline diabetes mellitus.  In the clinical trial done by Frank et al. 6, they evaluated the clinical response of diabetic cats to a high protein, low carbohydrate diet.  The study started with eighteen cats, but was reduced to nine (all of which were accounted for in the paper).  The paper clearly stated the inclusion criteria to be cats with diabetes mellitus for at least the previous four months, well managed on insulin, indoor cats and negative for FELV /FIV and the exclusion criteria were cats that were treated with oral hypoglycemic drugs or with other disease processes as indicated by physical exam, bloodwork and clinical history.  The design of the study involved standardizing the cats on a Hills W/D canned high fibre diet for 1-2 months prior to the start of the experimental period and then the cats were transitioned onto Purina DM canned for the three month study period.  The paper provided a decent nutrient analysis and measured fructosamine, glucose, owner’s observations and insulin dosage.  The conclusion that the authors made was that a cat on a high protein diet could have its insulin dosage decreased by fifty percent without an increase in fructosamine and that overall, the owner’s impressions of their animals appetites, activity level and urination volume was improved throughout the trial period.  However, because this paper had no blinding or randomization, there is a high risk of bias interfering with the noted results.  In addition to which, even with a significant decrease in fructosamine, only 2 of the 9 cats were considered to have appropriate fructosamine levels at the end of the study, the authors did acknowledge this and suggested that it was too early to see that change.  This study was also subject to a small sample size, did not measure owner compliance and allowed for the diet to consist of up to ten percent of treats.
Another clinical trial performed by Mazzaferro et al.7 evaluated the use of a low-carbohydrate diet, with or without acarbose, to determine if it was effective in improving glycemic control and reducing insulin requirements.  The trial involved twenty four cats, eighteen of which were fed a low carbohydrate and acarbose diet while the remaining six were fed the low carbohydrate diet only.  The inclusion criteria for the study were that none of the cats were controlled diabetics on entrance into the study and all the cats were overweight or historically overweight before clinical weight loss.  The exclusion criteria were that if any evidence of disease other than diabetes mellitus was found on physical examination, serum thyroxine testing, CBC and urinalyses, the cat was excluded.  In the study, all cats were fed according to their daily energy requirements with Science Diet Feline Growth (high protein and low carbohydrate) with no other food products allowed for four months.  A basic nutrient breakdown was provided and fructosamine and serum glucose were monitored.  The authors observed that  both serum glucose and fructosamine decreased significantly in both groups, but there was no significant difference between groups and as such concluded that acarbose did not improve glycemic control much (they do acknowledge that they might not see this difference due to low sample size) but that low carbohydrate, high protein diets significantly improve glycemic control.  This study was also subject to possible bias as there was no blinding or randomization done in the study, no measure of owner compliance and the study size was small.
A clinical trial that evaluated a commercially available moderate carbohydrate–high fibre food (Hill's Feline w/d canned) and a low carbohydrate–low fibre  food (Science Diet Feline Growth canned) to determine the effects  on glycemic control and insulin requirements in cats with diabetes mellitus written by Bennett et al 8  was also evaluated.  The study initially involved 82 cats, but 19 were excluded due to disease so the study was done on 63 cats.  The inclusion criteria stated was that the cats could be in the study if they had persistent hyperglycemia and persistent glucosuria for at least 2 weeks and were normal on physical examination, complete blood count, serum chemistry panel and urinalysis. All cats had serum thyroxine concentrations within normal reference range and were negative on FeLV/FIV ELISA assay.   The exclusion criteria was that if the cat had prior treatment with glucocorticoids, sex hormones, anabolic steroids or oral hypoglycemic agents 3 months prior to or since the diagnosis of diabetes, concurrent disease,  use of concurrent medications, dietary supplements or refusal to eat the provided study food the cat was excluded. The study design included each cat being randomly assigned to a treatment group and each cat was fed between 60-65kcal/kg/day for four months (no other foods were to be fed).  The diets were comparable in protein, such that fibre and carbohydrate were the main differences between the diets.  The authors provided a detailed nutrient analysis, monitored owner compliance and only the owners were blinded.  The study measured fructosamine, serum chemistry, CBC, urinalysis and owner observations.  Serum glucose was done randomly to monitor for complications of diabetic control but emphasis was placed on fructosamine and owner observation with regards to glycemic control.  The authors concluded that the cats on the low carbohydrate-low fibre diet had a higher chance of discontinuing insulin and that there was a significant decrease in fructosamine and glucose levels in all cats in the low carbohydrate-low fibre group and of the cats that were able to discontinue insulin in the moderate carbohydrate-high fibre group.  This paper did have some risk of bias due to the researchers not being blinded.
               The issue of fibre content in diets for diabetic cats was evaluated in a clinical trial cross-over study by Nelson et al. 9.  The authors performed the study to determine the effect of dietary insoluble fibre on control of glycemia in cats with diabetes mellitus.   The study initially involved 25 cats but was decreased to 16 that were evaluated in the trial (authors accounted for those that did not complete the study).  The inclusion criteria stated was that cats had to have diabetes mellitus for the previous 2-8 months while using the same amount of insulin daily.  The exclusion criteria was any signs of disease as determined by CBC, serum biochemistry, urinalysis, serum thyroxine and FeLv/FIV that was in addition to diabetes mellitus.  The study design involved two diets being made up by pet food companies that were the same except for fibre and carbohydrate (high fibre had lower carbohydrate) levels.  The cats were fed these diets for 24 weeks in each trial and owner compliance was monitored.  Everyone was blinded except for one researcher and the measured outcomes were glycated hemoglobin, insulin dosage, glucose pre-prandial and mean 12 hour glucose.  The authors observed significantly lower serum glucose levels in the high fibre diet when compared to the low fibre diet and concluded that feeding a diet with 12% DM of insoluble fibre to cats with diabetes mellitus is beneficial to their glycemic control.   This study was at some risk for bias based on the one researcher being aware of the treatments and was subject to a small sample size. 
When the results of all the previous papers about felids are taken into consideration, there seems to be a general conclusion that feeding a low carbohydrate/high protein diet is beneficial in glycemic control of cats with diabetes mellitus.  It is difficult to differentiate whether it is the high protein or the low carbohydrate that is the most beneficial to the cat however, it could be the combination of both as this is most consistent with the cats evolutionary feeding habits as a strict carnivore.  With regards to whether fibre is beneficial in the diabetic felid diet, the study by Nelson  et al. 9  was unable to separate the effects of having high fibre from the low carbohydrate that was in that same diet.   The study by Bennett et al. 8 seemed to find more beneficial effects in the diet that was low carbohydrate and low fibre when compared to the diet that was moderate carbohydrate and high fibre.  These findings may suggest that fibre can be beneficial, but is not as significant as low carbohydrate in the diet.
The evidence provided by these papers suggests that the pet food companies are making claims that coincide with the scientific literature that is currently available.  However, there are still considerable variations both within and between companies with regards to what “low carbohydrate and high protein” consists of.  Based on what was observed when obtaining data regarding diets from different companies, the probability of reaching an agreed upon optimal content of individual nutrients is unlikely to occur.
After the review of the literature obtained, there are two diets that best meet the suggested nutrient requirements of the scientific literature and as such we would recommend.  Hills M/D contained the highest protein and the second lowest carbohydrate content of all the diets evaluated and Purina DM had the lowest carbohydrate and third highest protein content as based on the typical analysis on a g/100kcal basis.  Both diets are also mid-range for cost when compared to the other diets evaluated.


Conclusions
Following our two week assignment we found that analyzing these diabetic dry formulas to be quite difficult as problems were encountered every step of the way.  For example, typical analyses for each diet were extremely hard to obtain in some cases; one company stated that the information was proprietary, another did not have the information, yet another had a very complicated network to get the information and was unable to supply it during the time of the project.  During the process of analyzing the diets we found that the nutritional information was often presented in different forms both within company brands and between companies.  Some would provide their information as an “as fed” percentage, a “dry matter” percentage, as nutrient density (g/1000 kcal), or any combination of these parameters, making it difficult to analyze the diets until they were all converted to a common denominator.  Also frustrating was the amount of nutrient information provided; some companies provided an extensive list of the nutrients analyzed including vitamins and minerals while other companies would not even provide the most basic analysis, such as carbohydrate content.  Those with more extensive nutrient lists allowed for a better and more accurate analysis of their diets.  During our phone conversations with the nutritional consultants at each company we found some more willing to provide information than others and some were much more knowledgeable than others.  In a few cases, it was very difficult to get a hold of a nutritional consultant.
               After analyzing these diabetes diets we found, in most cases, that claims made by the manufacturers were met.  However, it is important that there be one standard set out for all pet food companies to meet.  This standard should have a minimum and maximum value, setting a range for each nutrient; we found that there would be a highly variable range for each nutrient as all the company has to do is to meet a minimum standard.  For example, if the minimum carbohydrate standard was 10.0 g/100 kcal then the manufacturers could put in anything from 10.1 g/100 kcal to 40.0 g/100 kcal.  We also found that when comparing the commercial feline diets to a prey diet, none of the diets met prey diet standards, as such, perhaps a more appropriate comparison source should be considered (as only a small minority of pet owners would feed their cats mice as a diet).  Another problem we encountered was during our search for literature to support or refute the manufacturer’s claims, where we noticed many of their claims are based on findings presented in proceedings or from research by their own company.  We feel for these claims to be more credible they should be presented in a peer reviewed journal and that the research behind them should come from studies performed by independent researchers with no affiliation to the pet food industry.
               After our experience we have concluded that analyzing diets is not very practical.  There are too many diets and too much information to process to make this practical in a veterinary clinic setting.  To make comparisons much simpler and more accessible, the pet food companies should be putting their typical analysis, instead of their guaranteed analysis, on the bag of food.  Typical analyses also need to contain a minimum of listed nutrients such as protein, fat, carbohydrate, fibre (insoluble and soluble), moisture, calcium, phosphorus, magnesium, sodium, potassium, and vitamins (A, C, E, D).  If their diet contains specific nutrients, such as carnitine, that should also be included to facilitate analysis of their diets.  In doing so, the pet food companies would be providing veterinarians with appropriate and easily accessible information that would allow them to make the best food choice for their client’s pets; thus, allowing the pet food companies and veterinarians to work together to provide the best possible care to our pets.
References
1.      Graham PA, Maskell IE, Rawlings JM, Nash AS, Markwell PJ. Influence of a high fibre diet on glycaemic control and quality of life in dogs with diabetes mellitus. J Small Anim Pract 2002 Feb;43(2):67-73.
2.      Kimmel SE, Michel KM, Hess RS, Ward CR. Effects of insoluble and soluble dietary fiber on glycemic control in dogs with naturally occurring insulin-dependent diabetes mellitus. J Am Vet Med Assoc 2000;216:1076-81.
3.      Fleeman LM, Rand JS, Markwell PJ. Lack of advantage of high-fibre, moderate-carbohydrate diets in dogs with stabilised diabetes. J Small Anim Pract 2009 Nov;50(11):604-14.
4.      Mynatt RL. Carnitine and type 2 diabetes. Diabetes Metab Res Rev 2009;25(Suppl 1):S45-9.
5.      Hill SR, Rutherfurd-Markwick KJ, Ravindran G, Ugarte CE, Thomas DG. N Z Vet J 2009 Dec;57(6):313-18.
6.      Frank G, Anderson W, Pazak H, et al. Use of a high-protein diet in the management of feline diabetes mellitus. Vet Therap 2001 2(3):238-46.
7.      Mazzaferro E, Greco D, Turner A, Fettman M. Treatment of feline diabetes mellitus using an α-glucosidase inhibitor and a low-carbohydrate diet.  J Fel Med Surg 2003 5(3):183-9.
8.      Bennett N, Greco D, Peterson M, et al. Comparison of a low carbohydrate–low fiber diet and a moderate carbohydrate–high fiber diet in the management of feline diabetes mellitus.  J Fel Med Surg 2006 8(2):73-84.
9.      Nelson R, Scott-Moncrieff JC, Feldman E, et al. Effect of dietary insoluble fiber on control of glycemia in cats with naturally acquired diabetes mellitus.  J Am Vet Med Assoc 2003 216(7):1082-8.







Tables and Figures:

Manufacturer
Canine  Diets
Feline Diets
Prescription
Over the Counter
Prescription
Over the Counter
Purina
PVD DCO
ProPlan Weight Management
PVD DM
ProPlan Weight Management
MediCal / Royal Canin
Fibre
Pedigree Healthy Weight Control
Diabetic DS
Kitten 36
Hill's
w/d
Science Diet Adult Light
w/d
Science Diet Healthy Development
m/d
Iams
IVD Optimal Weight Control D
ProActive Health Weight Control
IVD Optimal Weight Control D
ProActive Health Kitten
Table 1. List of dry prescription and over the counter diets compared.


Table 2. Comparison of the composition of eight diabetes mellitus diets and their ingredients



Protein
Fat
Carbohydrate
Fibre
Insoluble Fibre
Soluble Fibre
Carnitine
Top Ingredients
NRC minimum requirements (g/100kcal)

5.0
2.3
16.4
1.0



Energy requirement (kcal/day)
666
g/100 kcal
Diet
Claims
Manufacturer's recommendations (Kcal/day)
PVD DCO
complex carbohydrates and dietary fibre to delay glucose absorption and minimize blood glucose fluctuations
640
6.9
3.4

2.1
5.0
1.1

ground yellow corn, dried beet pulp, poultry by-product meal, corn gluten meal, barley, beef tallow, pea fibre, dicalcium phosphate, dried whey
ProPlan Wt Mgmt
optimal protein:fat ratio to lose fat not muscle; high levels of fibre
674-785
7.5
3.6

1.6



chicken, brewers rice, poultry by-product meal, corn gluten meal, oat meal, corn bran, wheat flour, whole grain wheat, whole grain corn, animal fat, animal digest
MediCal Fibre
optimal fibre ratio; moderate fibre levels to improve satiety; L-carnitine for fat metabolism
318-445
8.0
3.6

4.7



chicken meal, tomato pomace, corn, rice, rice hulls, dried beet pulp, natural flavour, chicken fat, dried egg powder, dried brewer's yeast, herring meal, flax meal, apple pomace
Pedigree Wt Ctrl
less fat for weight management; high quality protein
574
7.8
3.0

1.2



meat and bone meal, chicken by-product meal, rice, ground yellow corn, wheat, beet pulp powder, natural poultry flavour, animal fat, wheat flour
Hill's w/d
increased fibre content to minimize blood glucose fluctuations to better manage diabetics
486-668
7.0
3.2
18.8
6.0
0.5
10.2
0.01
ground whole grain corn, powdered cellulose, chicken by-product meal, chicken liver flavour, soybean mill run, corn gluten meal, soybean oil, dried beet pulp, soybean meal
SD Adult Light
carnitine to metabolize fat and maintain lean muscle mass; fibre for satiety
516
9.0
3.2
17.3
5.3


0.01
ground whole grain corn, soybean mill run, chicken by-product meal, powdered cellulose, corn gluten meal, soybean meal, chicken liver flavour, soybean oil
IVD Wt Ctrl D
carnitine to metabolize fat; barley and grain sorghum regulates blood glucose and insulin response, reduced fat
441-567
8.1
2.7
14.5
0.85


0.001
ground whole grain sorghum, chicken by-product meal, ground whole grain barley, fish meal, dried beet pulp, chicken flavour, gum arabic, chicken fat, dried egg product, FOS, carboxymethylcellulose
ProActive Wt Ctrl
L-carnitine to help with weight loss
454-545
6.1
2.8
13.5
0.74


0.0009
corn meal, chicken by-product meal, ground whole grain sorghum, chicken, gourn whole grain barley, dried beet pulp, chicken flavour, chicken fat, dried egg product, brewer's dried yeast






Table 4. Comparison of the compositions of nine feline diabetes mellitus diets, their ingredients and costs.
Requirements


Protein
Fat
Fibre
Carbohydrates
Ca
P
$/day based on Rec. Company Intake for 6 kg cat



kcal/day
g/100Kcal

Energy Requirements

300








Prey Diet
  

15.1
5.5
0.9
0.5
0.7
0.5
0


Claims
Manufacturer's Rec. Caloric Intake (kcal/day)







Ingredients
MediCal Diabetic
Diabetic is a high protein, reduced carbohydrate, moderate energy diet that also contains antioxidants.
400
12.7
3.3
1
6
0.3
0.3
1.72
Chicken Meal, Corn Gluten Meal, Soy Protein Isolate, Corn, Pearled Barley, Chicken Fat, Natural Flavour, Brown Rice, Powdered Cellulose, Dried Beet Pulp
Royal Canin Kitten 36
Has prebiotics and digestible proteins as well as antioxidants. Contains  L-lysine and mannan-oligosaccharides (MOS) to stimulate the production of antibodies.
394






0.83
Chicken meal, brown rice, corn gluten meal, corn, chicken fat, dried egg powder, natural flavors, wheat gluten, dried beet pulp, L-lysine
Purina DM
High protein, low carbohydrates, source of omega-3 and omega-6 fatty acids and a high level of antioxidant.
444
12.9
4
0.3
3.4
0.4
0.3
0.89
Poultry by-product meal, soy protein isolate, corn gluten meal, soy flour, animal fat, corn starch, animal liver flavor, calcium carbonate, phosphoric acid, fish oil
Purina ProPlan Weight Management
High levels of protein along with essential vitamins and minerals, also contains antioxidants and omega fatty acids.
446
14.4
3.6

7.5
0.4
0.4
0.59
Chicken, brewers rice, corn gluten meal, poultry by-product meal, soy protein concentrate, wheat flour, fish meal, dried egg product, soy protein isolate, animal fat
Iams Weight Control D
L-Carnitine, reduced fat and appropriate protein levels and moderate fibre levels.
408
10.2
3.2
0.4
10.9


1.02
Chicken By-Product Meal, Corn Grits, Ground Whole Grain Sorghum, Corn Meal, Dried Egg Product, Dried Beet Pulp, Chicken Fat, Gum Arabic, Chicken Flavor, Fish Oil
Iams ProActive Kitten
Provides protein-rich nourishment, select natural ingredients have added vitamins, minerals and amino acids.
426
7.4
4.7
0.4
6.2
0.2
0.2
0.43
Chicken, Chicken By-Product Meal, Corn Meal, Corn Grits, Animal Fat, Dried Egg Product, Dried Beet Pulp, Natural Flavor, Fish Oil, Potassium Chloride
Hills W/D
Low in fat and calories, high carnitine, high in fibre and added antioxidants.
351
14
3.5
2.7
13.5
0.4
0.3
0.7
Chicken By-Product Meal, Corn Gluten Meal, Brewers Rice, Rice Flour, Powdered Cellulose, Chicken Liver Flavor, Soybean Oil, Calcium Sulfate, Potassium Sulfate, Choline Chloride
Hills M/D
Low carbohydrate, high protein, appropriate levels of fibre, high levels of taurine and arginine and added antioxidants.
360
14.8
6.3
1.7
4.2 
0.3
0.2
0.97
Chicken By-Product Meal, Corn Gluten Meal, Pork Fat , Pork Protein Isolate, Powdered Cellulose, Brewers Rice, Ground Whole Grain Corn, Dried Egg Product, Chicken Liver Flavor, L-Lysine
Science Diet Kitten Healthy Development
Contains antioxidants, DHA, taurine, high quality protein at ideal levels.
510
11.8
7.3
0.5
6.2
0.4
0.3
0.75
Chicken By-Product Meal, Ground Whole Grain Corn, Corn Gluten Meal, Pork Fat, Chicken Liver Flavor, Brewers Rice, Fish Oil, Flaxseed, Dried Egg Product, Soybean Mill Run



Table 3. Cost and amount to feed 666 kcal/day for each canine diet
Energy requirement (kcal/day)
cups/day
cost/day


Diet


Purina Veterinary Diet DCO
2.08
$2.75

Purina ProPlan Weight Management
1.98
$0.70

MediCal Fibre Formula
2.62
$1.46

Pedigree Healthy Weight Control
2.61
$0.56

Hill's Prescription Diet w/d
2.74
$1.31

Hill's Science Diet Adult Light
2.26
$0.86

IVD Optimal Weight Control D
2.64
$1.53

Iams ProActive Healthy Weight Control
1.83
$0.60







Figure 1. Graphic presentation of amount and cost to feed for each canine diet



Figure 2. Comparison of recommended daily intakes.



Energy requirement = 300 kcal/d
cups/day
cost/day


Diet


MediCal Diabetes DS
0.94
$1.72

Royal Canin Kitten 36
0.76
$0.83

Purina DM
0.50
$0.83

Purina ProPlan Weight Management
0.67
$0.59

IVD Optimal Weight Control D
0.92
$1.02

Iams ProActive Kitten
0.70
$0.43

Hill's Prescription Diet w/d
1.07
$0.70

Hill’s Prescription Diet m/d
0.63
$0.97

Science Diet Healthy Development
0.59
$0.75







 Table 5. Comparison of recommended daily intakes.





Brand
MediCal Diabetic Dry
Royal Canin Kitten 36 Dry
Purina DM Dry
Purina Proplan Weight Management Dry
Iams Weight Control D Dry
Proactive Health Kitten Dry
Hills  W/D Dry
Hills  M/D Dry
Science Diet Kitten Healthy Development
Energy Requirement (kcal/day)
               300
               300
              300
                    300
             300
               300
               300
                300
                     300
Manufacturers Recommendations
(kcal/day)
400
394
444
446
408
426
351
360
510
Difference
               100
                  94
              144
                    146
             108
               126
                 51
                  60
                     210
Table 6. Cost and amount to feed 300 kcal/day for each feline diet

Figure 3. Graphic presentation of the amount and the cost to feed for each feline diet.

Comparison of commercial weight control diets for cats and dogs

Weight Control

Introduction
There are many weight control diets available on the market for pets.  This can be confusing for consumers to decide which diet is best for the health of their pet.  Many factors contribute to obesity in pets, including lack of exercise and excessive calorie intake.  Increased body fat can result in a decreased lifespan and increased morbidity in pets. Weight loss is best achieved by reducing caloric intake and increasing exercise.  When reducing caloric intake it is important to prevent loss of lean body weight by providing adequate protein in the diet.  An appropriate weight loss diet should be restricted in calories, be low in fat, have increased protein content and have increased dietary fibre.  Veterinarians are expected to be knowledgeable about the various diets available to clients and the benefits of each diet, but often lack the required information.

Methodology
Various commercial weight control diets from various pet food companies were compared to each other.  Comparisons were made based on food analysis, ingredients, and cost to feed per day.




Results
Diet
Company claims
Kcal/100g
Crude protein
Guranteed analysis (%)

Crude fat Guranteed analysis (%)

Crude fibre Guranteed analysis (%)

Special ingredients
Approximate
cost to feed per day (10 kg dog)

Medi-Cal / Royal Canin canine dry food diets:


Calorie Control
Increased levels of protein, essential fatty acids, vitamins and minerals relative to calories to avoid nutritional deficiencies while restricting calories
Normal fibre levels to maintain a normal stool volume
359
25
7.5
5.7

$0.73

Fibre diet
Moderate fibre levels which may improve satiety in individual dogs during a weight loss program
Reduced energy and fat levels for weight loss

286.9
27.5
8.0
18.3
L-carnitine
$0.88


Satiety support
Increased amounts of high quality protein sources (chicken meal, corn and corn gluten, wheat gluten) provide balanced nutrition during weight loss and help preserve lean body mass

289.7
30
9.5
17.5
L-carnitine
$1.14

Weight control/ mature
Reduced energy and fat levels to help prevent weight gain
Low fat content to ease the digestive workload
Moderate fibre levels, including fructo-oligosaccharides (FOS), in an optimal ratio of soluble and insoluble fibre to maintain digestive tract health

289
16.0
7.0
6.0
L-carnitine
$0.65

Pedigree dry food for overweight dogs
10% less fat than Pedigree Healthy Vitality® food for dogs to support healthy weight management
High Quality Protein

329
25.5
7.5
4.0
Vitamin E
Ascorbic acid
Zinc
$0.41

Iams dry canine diets:


Restricted calorie
Have patented carbohydrates and specialized ingredients so your pet can feel full while consuming fewer calories
The result is that he can maintain muscle mass while losing fat
100.2
22.0
6.5
4.0
L-carnitine
$0.85

Proactive Health
Formulated with L-Carnitine to gradually return your dog to a healthy weight
Natural sources of protein sourced from chicken and egg helps build strong, firm muscles
348.5
20.0
10.0
5.0
L-carnitine
$0.29

Purina dry canine diets:


Overweight management
Contains high levels of protein to stimulate metabolism and promote fat loss while maintaining lean muscle
It also has low levels of fat and calories to encourage weight loss, and an appropriate level of fiber to help your dog feel satisfied after eating

262.4
26.0
4.0
16.0

$0.66

Beneful Healthy Weight
Reduced-calorie dog food that helps keep your dog happy and healthy – with 10% fewer calories than Beneful Origial
High-quality protein, including natural soy, helps maintain lean muscle mass during weight loss

314.3
25.0
7.0
9.0

$0.46

Hills dry canine diets


w/d
Moderately high fiber levels provide a feeling of fullness
Helps stabilize and minimize fluctuation of blood glucose levels in diabetic dogs

298.6
15.0
6.0
20.0
L-carnitine
$1.26

Science diet canine adult light
Reduced calorie content to help control weight
It has a high fiber content to keep your dog satisfied between meals

299.7
24.5
8.8
14.6
L-carnitine
$0.47












FELINE
Diet
Company claims
Kcal/100g
Crude protein
Guaranteed analysis (%)

Crude fat Guaranteed analysis (%)

Crude fibre Guaranteed analysis (%)

Ingredient Comparison
(Top 5 Ingredients listed)
Approximate
cost to feed per day
 (4.5-5.5 kg cat)
Medi-Cal / Royal Canin feline diets:



Calorie Control
Dry Food

Indicated for weight loss in overweight or obese cats.  Increased levels of protein, essential fatty acids, vitamins and minerals relative to calories to avoid nutritional deficiencies while restricting calories
328
43.9
10.3
3.8
Chicken meal, rice, corn gluten meal, natural flavour, powered cellulose
$0.80
Calorie Control
Canned Food

Indicated for weight loss in overweight or obese cats.  Increased levels of protein, essential fatty acids, vitamins and minerals relative to calories to avoid nutritional deficiencies while restricting calories
66.7
54.8
19.4
3.5
Water, Pork by-products, chicken by-products, dried egg, powdered cellulose
$3.00
Weight Control
Dry Food
Adult maintenance for mildly overweight cats.  Specifically formulated to prevent struvite crystals from forming by managing urine pH and urine mineral concentrations.
367
35.9
12.0
3.7
Rice, chicken meal, corn gluten meal, corn, pea fibre
$1.27
Weight Control
Canned Food
Adult maintenance for mildly overweight cats.  Specifically formulated to prevent struvite crystals from forming by managing urine pH and urine mineral concentrations.
85.5
42.5
18.5
4.5
Water, pork by-products, chicken liver, pork, rice flour

Reducing
Dry Food
Indicated for weight loss in overweight cats.  Increased protein with restricted calories to maintain lean body mass while losing weight.  Increased nutrients and vitamins to maintain nutritional balance.  Excellent for diabetic cats.
327
42.9
8.2
3.3
Rice, chicken meal, corn gluten meal, potato protein, corn
$1.35
Reducing
Canned Food
Indicated for weight loss in overweight cats.  Increased protein with restricted calories to maintain lean body mass while losing weight.  Increased nutrients and vitamins to maintain nutritional balance.  Excellent for diabetic cats.
68.5
50.6
17.5
0.6
Water, chicken liver, pork by-products, mackerel, shrimp

Iams dry feline diets:



Weight loss/Restricted calorie
Dry Food
Indicated to nutritionally manage overweight cats and to maintain obese prone cats.  Contains moderate amount of fiber as well as omega fatty acids.
344.8
32.6
10.2
2.3
Chicken by-product meal, corn grits, corn meal, ground whole grain sorghum, dried beet pulp
$1.00
Weight loss/Restricted calorie
Canned Food
Indicated to nutritionally manage overweight cats and to maintain obese prone cats.  Contains moderate amount of fiber as well as omega fatty acids.
101
10.3
3.6
0.39
Chicken broth, chicken, whitefish, beef liver, chicken liver
$2.13
Weight  Control
Dry Food
Indicated to nutritionally manage overweight cats and to maintain obese prone cats.  Contains moderate amount of fiber as well as omega fatty acids.
350.3
35.7
11.3
1.4
Chicken by-product meal, corn grits, ground whole grain sorghum, corn meal, dried egg product
$0.91
Proactive Health Light
Dry Food
Indicated to help cats lose weight without losing energy.  Contains a special blend of carbohydrates as well as L-carnitine to keep cats energized and feeling full.
354.5
32.3
13.2
1.6
Chicken by-product meal, corn grits, corn meal, chicken fround whole grain sorghum

Purina feline diets:



Overweight management
Dry Food
Contains high levels of protein to stimulate metabolism and promote fat loss while maintaining lean muscle
It also has low levels of fat and calories to encourage weight loss, and a high level of fiber to help your cat feel satisfied after eating

324
56.2
8.5
5.6
Corn gluten meal, wheat gluten, soybean meal, poultry by-products meal, oat fiber
$0.77
Overweight management
Canned Food
Contains high levels of protein to stimulate metabolism and promote fat loss while maintaining lean muscle
It also has low levels of fat and calories to encourage weight loss, and a high level of fiber to help your cat feel satisfied after eating

82.3
9.0
GA
2.0
GA
3.0
GA
Water, liver, chicken, meat by-products, corn gluten meal
$3.55
ProPlan Weight Management
Dry Food
Designed to help overweight cats lose weight.  Contains antioxidants to maintain a strong immune system.  Contains a high level of protein and omega fatty acids to maintain a healthy hair coat and skin.

398
50.3
12.8
1.1
Chicken, brewers rice, corn gluten meal, poultry by-product meal, soy protein concentrate
$0.66
ProPlan Weight Management
Canned Food
Designed to help overweight cats lose weight.  Contains antioxidants to maintain a strong immune system.  Contains a high level of protein and omega fatty acids to maintain a healthy hair coat and skin.

88.2
12.0
GA
2.0
GA
1.5
GA
Chicken, brewers rice, corn gluten meal, poultry by-product meal, soy protein concentrate
$3.06
Hills dry feline diets



w/d
Dry Food

Indicated for weight control and healthy digestion.  Moderately high fiber levels provide a feeling of fullness
Helps stabilize and minimize fluctuation of blood glucose levels in diabetic cats.

322.7
39.0
9.8
7.6
Chicken by product meal, corn gluten meal, brewers rice, rice flour, powdered cellulose
$0.61
w/d
Canned Food

Indicated for weight control and healthy digestion.  Moderately high fiber levels provide a feeling of fullness
Helps stabilize and minimize fluctuation of blood glucose levels in diabetic cats

81.1
39.6
16.6
1.6
Water, pork liver, pork by-products, chicken, powdered cellulose
$2.06
r/d
Dry Food

Indicated for weight reduction of overweight cats.  Formulated to reduce body fat by 20% in three months.  High fiber levels provide a feeling of fullness.
301.8
36.9
9.3
13.6
Chicken by product meal, brewers rice, corn gluten meal, powdered cellulose, chicken liver flavour
$0.73
r/d
Canned Food

Indicated for weight reduction of overweight cats.  High fiber levels provide a feeling of fullness.
73.3
37.5
9.2
15.4
Water, pork liver, powdered cellulose, pork by-products, corn starch
$2.18
Science diet feline adult light
Dry Food
Indicated for maintenance of healthy body weight in obese prone cats.  High fiber to maintain satiety.  Contains antioxidants to maintain healthy immune system.

320.6
35.1
9.5
6.9
Brewers rice, chicken by-product meal, corn gluten meal, powdered cellulose, ground whole grain corn
$0.55
Science diet feline adult light
Canned Food
Indicated for maintenance of healthy body weight in obese prone cats.  High fiber to maintain satiety.  Contains antioxidants to maintain healthy immune system.

88.4
35.6
14.2
10.1
Water, pork liver, pork by-products, chicken, powdered cellulose
$1.43
















Results
Medi-cal satiety support contained the highest guaranteed protein content while the Medi-cal weight control/mature and Hills w/d diets were on the lowest end of the scale for protein content.  Iams proactive health and Medi-cal satiety support were highest in guaranteed analysis of fat content and Purina OM diet was the lowest in fat.  Based on grams/day recommended fed amount, Iams restricted calorie, Medi-cal calorie control, Purina OM and Hills w/d diets all do not meet the required daily fat as per the NRC requirements.  Iams diets in general contained low fibre content, and as per their website, they do not believe in increasing the fibre content of their food for weight control diets.  The diets highest in fibre included Medi-cal fibre diet and satiety support, Purina OM and Hills w/d.  Many of the diets contained L-carnitine.  Medi-cal calorie control and Pedigree over the counter brand did not contain it and none of the Purina weight control diets contained it.  In most cases, what these diets advertised on the bag (for example high fibre, or L-carnitine for weight loss) was reflected in their ingredient list.  Actual values for amounts of L-carnitine present in the diet could not be found.
For dogs, Hills w/d and Medi-cal satiety support were the most expensive diets to feed on a daily basis. Iams restricted calorie was the least expensive prescription diet and its over the counter Proactive health diet was the cheapest diet compared.  For cats, Medi-Cal/Royal Canin prescription diets were the most expensive to feed on a daily basis.  In general, a canned food diet is about twice as expensive as a dry food diet.  In all cases, the over the counter diets were cheaper than the prescription diets and although they were similar in ingredient lists, in general, they had more fat and less fibre than the prescription diets.
For cats, when comparing kcal/100, within Medi-Cal/Royal Canin, the reducing formula and calorie control were pretty comparable.  The weight control formula was higher in kcal.   Within Iams, the weight loss/restricted calorie formula was only very slightly lower in kcal than the proactive light formula.  Within Hill’s, the w/d and Science Diet Adult Light formulas have comparable kcal within their diets.  The r/d formula has a lower kcal/100g.
For feline dry diets, all of the diets were very similar in claims (except for those for weight control versus weight loss).  All diets were also similar in ingredient content.  Protein is important for weight loss.  Purina diets were both highest in protein (significantly).  Generally speaking, the diets that claim they’re for weight loss vs. weight control were lower in fat and kcal/100g.  The exception is Hill’s:  all three formulations, including the OTC diet, were comparable in crude fat content.  However, the r/d formula had lower kcal/100g.  Fiber is important for feeling full.  Most of the diets claimed to increase their fiber content to help your pet’s satiety (except for Iams).  Hill’s formulas were highest in crude fiber, the highest being Hill’s r/d.  In all cases, the OTC diet was cheaper to feed and not remarkably different except that they had higher kcal/100g.  The kcal/100g between all diets was fairly comparable.  Hill’s r/d, which claims it’s formulated for weight loss, had the lowest kcal/100g.  Purina’s OTC diet (Pro Plan Weight Management) had the highest kcal/100g.  It is important to evaluate the feeding guidelines in association with kcal/100g. 
For feline canned diets, comparison was difficult because not all companies formulated canned diets.  All of the diets were very similar in claims (except for those for weight control versus weight loss).  All diets were also very similar in ingredient content.  Since protein is important for weight loss, Medi-Cal/Canin diets were highest in protein.  Generally speaking, the diets that claim they’re for weight loss vs. weight control were lower in fat and kcal/100g.  The exception is Iams:  The Weight Loss diet was very low in crude fat content.  In all cases, the OTC diet was cheaper to feed and not remarkably different except that they had higher kcal/100g.  The kcal/100g between all diets was fairly comparable.  Medi-Cal/RC Reducing, which claims it’s formulated for weight loss, had the lowest kcal/100g.  It is important to evaluate the feeding guidelines in association with kcal/100g. 

Discussion
Obesity can lead to many diseases processes such as diabetes mellitus, dermatologic, orthopedic, and oral disease, hepatic lipidosis, and urinary tract infections.  Treatment of obesity typically includes a safe degree of energy restriction through the diet to cause a negative energy balance and promote weight loss. 
The goal of many weight loss diets is to provide a diet that is low in fat, high in protein and has an increased fibre content which will result in reduced calorie intake.  A diet with a high protein content will help to promote weight loss while preventing loss of lean body mass (Diez et al. 2002).  Studies have shown that a weight loss in dogs can be enhanced by a high protein and low carbohydrate diet (Bierer and Bui, 2004).  Many of the weight loss diets compared were relatively high in protein (except Medi-cal weight control/mature and Hills w/d diets). 
L-carnitine is a quaternary ammonium compound that is synthesized from the amino acides lysine and methionine.  It is required for the transport of fatty acids during the breakdown of lipids for the generation of metabolic energy.  Many of the weight loss diets contain L-carnitine as an additional supplement in the food.  It has been shown to increase the rate of weight loss in dogs and cats without adverse effects (Sunvold et al. 1998).  Notably, none of the Purina weight control food contained this compound and neither did Medi-cal calorie control diet or its over the counter diet Pedigree for overweight dogs. 
High fibre diets are also indicated for promoting weight loss by contributing to satiety while limiting the number of calories present in the diet.  A high protein high fibre diet can help obese dogs lose weight (German et al. 2010).  The amount of fibre present in weight control diets was variable.  Some diets contained very high amounts of fibre (Medi-cal fibre diet and satiety support, Purina OM and Hills w/d) while others contained low amounts of fibre (Iams restricted calorie and proactive health).
The diets that claim to help your pet lose weight versus control weight were less in kcal/100g, which is appropriate and expected.  The Iam’s veterinary formula is very similar in kcal versus their “over-the –counter” formula, which recommends a lower amount to be fed per day. 
For cats, feeding a canned diet versus a dry diet has been a controversial topic at best.  Although an all canned diet is more costly to feed a cat, many veterinarians believe that there is more success in regards to weight loss with all canned diets.  Canned food has less carbohydrates and almost always less calories per mouthful.  Clients are also far less likely to overfeed canned food.  However, canned diets are generally higher in fat content, which is counter productive for a weight loss diet.  Since our goal is to maintain lean muscle mass (which burns more calories than fat), our weight loss diets require high protein.  Canned diets generally have less protein versus dry diets.  Note, this is not true for all diets.  It is important to compare the crude protein and fat for dry and canned diets in the same formula.
Canned food is not necessarily better for weight loss, but any weight loss program requires energy restriction, which for some owners and cats is more acceptable with a higher volume of food (as in high moisture canned food).  Canned food contains a significantly higher amount of water, which can help with obese cats who have other disease processes in conjunction that require an increased amount of water in the diet (for example, diabetes mellitus).  Other factors are also present that contribute to this debate.  For example, it has been though that dry diets cause an increased amount of dental disease.  This has been another controversial debate.
For cats, our recommendation for weight loss with a dry diet is Hill’s r/d.  Our recommendation for weight loss with a canned diet is Medi-Cal Reducing Formula or Hill’s r/d formula.

Conclusion
The claims made on the bags for ingredient content were comparable to the ingredients found within the diets.  For example, a diet promoting fibre for weight loss would have high guaranteed fibre content.  The studies to support high fibre, high protein, and that L-carnitine all promote weight loss are mostly funded by the pet food companies themselves which may introduce a possible bias.  Also exact amounts of L-carnitine present in each diet were not available to compare.  For many diets, all the relevant information could not be found on the bag or website but could be obtained by phoning the company help line.  In my experience dealing with the companies over the phone, they were very helpful and friendly.

References
Bierer T.L. and L. M. Bui.  (2004)  High-Protein Low-Carbohydrate Diets Enhance Weight Loss in Dogs.  J. Nutr., 134(8): 2087S - 2089S.
Diez, M. et al.  (2002)  Weight loss in obese dogs:  Evaluation on a high protein, low carbohydrate diet. J. Nutr. 132:1685S-1687S.  (study was supported by Royal Canin)
German, A.J. Et al.  (2010) A high protein high fibre diet improves weight loss in obese dogs .  The Veterinary Journal, 183: 294-297.  (this paper was supported by Royal canin)
Harte, J. Et al. The clinical and metabolic effects of rapid weight loss in obese pet cats and the influence of supplemental oral L-carnitine.  J. Internal vet med 14: 598-608
Sunvold GD, Tetrick MA, Davenport GM, Bouchard GF. Carnitine supplementation promotes weight loss and decreased adiposity in the canine. Proceedings of the XXIII World Small Animal Veterinary Association. p.746. October, 1998  (this study was supported by Iams)
Villaverde, C. Et al.  Energy restriction resuls in a mass-adjusted decrease in energy expenditure in cats that is maintained after weight regain.  Journal of Nutrition 138: 856-860

Hills website: www.hillspet.com
Iams website: www.iams.com
Medi-cal/Royal canin website: http://www.medi-cal.ca/
Purina website: www.purina.ca

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