Obesity is one of the most common health problems of dogs and cats, with between 22% and 44% of the canine and feline populations in the United States currently overweight or obese.1,2 Obesity is associated with numerous diseases, including pancreatitis,3 osteoarthritis,4 dermatologic disease,5 diabetes,5,6 and respiratory tract disease.7 In addition, obesity may contribute to a shorter lifespan.4
It has been reported8 that 30% to 40% of dogs and cats will overeat and become overweight or obese if provided food ad libitum. Therefore, although all issues that predispose pets to obesity should be addressed (eg, lack of exercise and behavioral patterns for pets and owners), nutritional modification is a key component in a successful weight loss program. To reduce calorie intake, it is necessary to have information on calorie requirements of pets as well as the calorie content of foods. Although many consumers are aware of the nutritional information labels on human foods, nutritional information on pet foods differ substantially from those for human products. Currently, there are no requirements mandating that calorie content be provided on pet food labels, except for products bearing the terms lite, light, low calorie, less calorie, or reduced calorie or words of similar designation.9 For foods with a designation of lite, light, or low calorie, the AAFCO Model Pet Food Regulations9 also require adherence to maximum kilocalorie per kilogram restrictions and that the manufacturers state the kilocalorie per kilogram content on the label. However, there can be variability in the calorie density of low-calorie pet foods, and some labels of pet foods imply a low-calorie status without use of those specific terms. Therefore, pet foods that may be purchased by owners (through a veterinarian only or as an over-the-counter product) could have wide variation in calorie density. This can make it difficult for owners to select an optimal diet for weight loss of their pets as well as for veterinarians trying to assist in nutritional modification for their patients.
In addition to the variability in calorie density among diets, there is variation among pet food manufacturers with regard to the method by which feeding directions for normal-weight animals are determined. This, coupled with individual variation among animals, can make it difficult to use the feeding directions effectively in an animal of optimal body condition. The situation is compounded when weight loss is required in an overweight or obese pet for which greater calorie restriction is necessary. Some veterinarians may make specific recommendations of a diet and amount to be fed to animals that need to lose weight; however, many veterinarians and pet owners rely on the recommendations in a pet food's label. Therefore, the label recommendations for weight loss in pet foods marketed for this indication are likely a key source for the amount of a diet actually fed to a pet.
Preventing and treating obesity is an important component of optimal pet care. However, as a result of variability among diets and recommendations for weight loss as well as the inherent variation among pets, weight loss programs for overweight or obese pets are a challenging endeavor for pet owners and veterinarians. Although the reason for limited success in weight management in companion animals is likely multifactorial, the lack of information available to veterinarians and consumers about calorie density and appropriate feeding amounts for commercial pet foods likely plays an important role. Therefore, the objective of the study reported here was to investigate the calorie density, feeding directions, and price for commercially available diets marketed for weight loss in pets.
Materials and Methods
Commercially available diets for cats and dogs that might be purchased for weight loss on the basis of label information were included in the study. Various types of locations were surveyed that reflected common locations at which consumers would be able to obtain diets designed for weight loss of pets, including 2 pet specialty stores, 1 discount mass merchandiser, 1 supermarket, and 1 veterinary hospital. A range of label descriptions implying weight loss was accepted, such as the terms weight loss, weight management, overweight, or calorie reduction and images representative of overweight body condition. Diets were allocated into 2 categories: diets with weight management claims and feeding directions for weight loss and diets with weight management claims on the label but no specific feeding directions for weight loss. Label statements in the second category of diets included obese prone, to maintain healthy weight, avoid unwanted weight gain, lose excess weight, and reduced calorie.
For canned canine diets, a container size of 340 to 426 g (12 to 15 oz) was selected for comparison, whereas for feline diets, a container size of 142 to 170 g (5 to 6 oz) was used for comparison. Calorie density for each diet was determined on the basis of label information (when provided) or by contacting the manufacturer. Calorie density was compared with the AAFCO maximums for light, lite, or low-calorie diets (canine diets, < 3,100 kcal/kg [< 1,409 kcal/lb] of diet for dry foods and < 900 kcal/kg [< 409 kcal/lb] of diet for canned foods; feline diets, < 3,250 kcal/kg [< 1,477 kcal/lb] of diet for dry diets and < 950 kcal/kg [< 432 kcal/lb] of diet for canned diets).9 Recommended energy intake for each diet was determined by calculating the calories recommended for weight loss in accordance with feeding directions for a selected standard current body weight (36.4 kg [80 lb] for canine diets and 5.5 kg [12 lb] for feline diets). These standardized body weights represented common scenarios of obese pets examined by veterinarians. Recommended energy intake was compared with the RER for the standard body weight by use of the following equation8: RER = 70 × (body weight in kg)0.75. When a range of values was provided for the feeding directions, mean of the range was used for calculations. All diets, except for 2 (a feline and a canine version of the same diet) used current weight, rather than goal weight, for recommended feeding suggestions. Thus, except for those 2 diets, a 25% reduction in the standard current body weight was considered the goal weight, which was 27.3 kg (60 lb) for the canine diet and 4.1 kg (9 lb) for the feline diet.
Price per weight of diet and price per 100 kcal of diet were calculated on the basis of the least expensive option commercially available to consumers. If multiple sizes of the same product were available at 1 location or at multiple locations, the least expensive option for each product was chosen on the basis of price per weight of diet.
Data were reported as median and range. The Mann Whitney U test was used to compare feeding directions and price between groups (eg, canine vs feline, canned vs dry, veterinarian product [ie, those that could only be purchased from a veterinarian] vs over-the-counter product, and diets with specific weight loss recommendations vs diets with implied weight loss claims). Commercial statistical softwarea was used for all analyses. Values of P < 0.05 were considered significant.
Results
Diets with weight management claims and feeding directions for weight loss—Information was evaluated for 72 diets with feeding directions for weight loss, which included 40 canine diets (30 dry and 10 canned) and 32 feline diets (24 dry and 8 canned). Diets varied in calorie density on both a volume basis (ie, kilocalories per cup [1 cup = 237 mL]) or kilocalories per can and a weight basis (ie, kilocalories per kilogram of diet; Table 1). Calorie density on the basis of kilocalories per kilogram of diet was greater than the AAFCO maximum calorie density for light foods for 42 of 72 (58%) diets (22 canine diets [20 dry and 2 canned] and 20 feline diets [16 dry and 4 canned]).
Calorie density of canine and feline diets with feeding directions forweight loss.*
| Species | Dry diets | Canned diets | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| n | kcal/cup† | kcal/kg of diet | n | kcal/can‡ | kcal/kg of diet | |||||
| Median | Range | Median | Range | Median | Range | Median | Range | |||
| Canine | 30 | 297 | 217–395 | 3,295 | 2,726–3,875 | 10 | 309 | 189–398 | 857 | 533–1,002 |
| Feline | 24 | |||||||||
The AAFCO maximums for foods labeled as light, lite, or low calorie were < 3,100 kcal/kg (< 1,409 kcal/ lb) of diet for dry canine diets, < 900 kcal/kg (< 409 kcal/lb) of diet for canned canine diets, < 3,250 kcal/kg (< 1,477 kcal/lb) of diet for dry feline diets, and < 950 kcal/kg (< 432 kcal/lb) of diet for canned feline diets.g
One cup = 237 mL.
For canned canine diets, container size of a can was 340 to 426 g (12 to 15 oz), whereas for feline diets, container size of a can was 142 to 170 g (5 to 6 oz).
n = Number of diets.
To convert kilocalories per kilogram of diet to kilocalories per pound of diet, divide value by 2.2.
Recommended calorie intake also varied among diets with weight management claims and feeding directions for weight loss. Recommended calorie intake for dogs on the basis of feeding directions ranged from 0.73 to 1.30 × RER for current weight (median, 1.00 × RER for current weight). For cats, recommended calorie intake on the basis of feeding directions ranged from 0.67 to 1.38 × RER for current weight (median, 0.95 × RER for current weight). Cost ranged from $1.16 to $10.25/kg ($0.53 to $4.66/lb) of diet (median, $4.37/kg [$1.99/lb] of diet) and from $0.04 to $1.11/kcal (median, $0.15/100 kcal).
No significant difference was found in the recommended calorie intake between canine and feline diets (P = 0.17) or between canned and dry diets (P = 0.57). Veterinarian diets (ie, those that could only be purchased from a veterinarian) had a significantly (P < 0.001) lower median recommended calorie intake (0.89 × RER), compared with the value for the over-the-counter diets (1.09 × RER).
Diets with implied weight management claims but without feeding directions for weight loss—Information for 21 diets with implied weight management claims on the label but without specific feeding directions for weight loss were analyzed separately. This included 4 canine diets (3 dry and 1 canned) and 17 feline diets (13 dry and 4 canned). Diets ranged in calorie density on both a volume basis and on a weight basis (Table 2). Calorie density on a kilocalorie per kilogram basis was greater than AAFCO maximum calorie density for light foods for 10 of 21 (48%) diets (2 canine diets [2 dry and 0 canned] and 8 feline diets [7 dry and 1 canned]).
Calorie density of canine and feline diets without feeding directions for weight loss.*
| Species | Dry diets | Canned diets | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| n | kcal/cup† | kcal/kg of diet | n | kcal/can‡ | kcal/kg of diet | |||||
| Median | Range | Median | Range | Median | Range | Median | Range | |||
| Canine | 3 | 352 | 352–440 | 3,611 | 3,065–3,615 | 1 | 322 | NA | 871 | NA |
| Feline | 13 | 400 | 281–478 | 3,473 | 3,143–4,017 | 4 | 145 | 143–147 | 937 | 916–1,095 |
NA = Not applicable.
See Table 1 for remainder of key.
Recommended calorie intake for dogs on the basis of feeding directions ranged from 1.31 to 1.47 × RER for current weight (median, 1.41 × RER for current weight). For cats, recommended calorie intake on the basis of feeding directions ranged from 0.99 to 1.55 × RER for current weight (median, 1.26 × RER for current weight). For diets with implied weight management claims but without feeding directions for weight loss, cost ranged from $1.16 to $9.50/kg ($0.53 to $4.32/lb) of diet (median, $4.40/kg [$2.00/lb] of diet) and from $0.04 to $0.84/100 kcal (median, $0.16/100 kcal).
Overall dietary comparisons—Calorie density on a volume basis was significantly lower in diets that had specific feeding directions for weight loss, compared with the value for diets that had implied weight loss claims without specific feeding directions for weight loss, for both canine (P = 0.02) and feline (P = 0.01) diets. However, there was no difference in calorie density on a weight basis for diets that had specific feeding directions for weight loss, compared with the value for diets that had implied weight loss claims, for both canine (P = 0.41) and feline (P = 0.80) diets. Median recommended calorie intake was significantly (P < 0.001) lower for diets that had specific feeding directions for weight loss (1.00 × RER) than for diets that had implied weight loss claims (1.30 × RER). There was no significant difference in median price per kilogram (P = 0.66) or price per 100 kcal (P = 0.99) between diets with feeding instructions for weight loss and those without. However, there was a significant difference in median price per kilogram (P = 0.009) and price per 100 kcal (P < 0.001) between all canned and dry diets included in the study.
Discussion
Nearly 100 diets were readily identified that had feeding directions for weight loss or implied weight management claims. These diets had a wide variation in marketing claims (eg, weight loss, obese prone, to maintain healthy weight, avoid unwanted weight gain, lose excess weight, and reduced calorie), but more importantly, there was a > 2-fold difference in calorie density of these foods on both a volume and weight basis. More than half of all foods in the study had a calorie density greater than the AAFCO maximum calorie density for light diets, which makes it difficult to successfully attain weight loss without careful control of calorie intake.
Although there was wide variability in calorie density of the diets included in the study, it would be potentially possible to achieve successful weight loss in an animal by adjusting calorie intake accordingly. For example, if a cat should be fed 235 kcal/d to lose weight, an owner could be instructed to feed 1 cup of a diet with a calorie density of 235 kcal/cup or to feed 0.5 cups of a diet with a calorie density of 470 kcal/cup, provided that the reduced amount of the diet with the higher calorie density still provided adequate nutrients.
However, the other problem detected in the study reported here was the wide range in feeding directions and high variability in estimates of calorie requirements for weight loss, which make successful weight loss unlikely with most diets. This range is not surprising because even within the veterinary community, there is variation in recommendations for calorie requirements of healthy as well as obese animals. The RER in cats and dogs has most commonly been calculated by use of the following equation: RER = 70 kcal × (body weight in kg)0.75, although other equations have also been suggested.10 Recommendations for the MER of clinically normal adult animals vary among sources, ranging from approximately 1.2 to 1.88 × RER.8,10 When applying these equations for determining appropriate energy intake of obese animals, the recommendations have even more variation.
Calorie requirements for weight loss have been calculated by use of numerous techniques, including the use of current body weight (eg, 40% to 60% of MER for current body weight), optimal weight (eg, 50% to 75% of MER for optimal weight), current calorie intake (eg, 80% of current calorie intake), or rate of weight loss (eg, 1% to 3% of body weight/wk).11–13 Regardless of the equation used, most pets require calorie restriction to less than the RER for current body weight (and some must be substantially less than the RER) to achieve weight loss. By use of the standard weights for cats and dogs we selected for our study, recommendations to achieve weight loss would range from 0.73 to 1.13 × RER for optimal weight.13 The canine diets in the study reported here ranged from 0.73 to 1.30 × RER for current weight for diets with specific feeding directions for weight loss and from 1.31 to 1.47 × RER for current weight for diets with implied weight management claims. The results were similar for cats, with a range of 0.67 to 1.38 × RER for current weight for diets with specific weight loss directions and from 0.99 to 1.55 × RER for current weight for diets with implied claims. In fact, many animals would likely gain weight if owners were to adhere to these feeding directions. This confirms the great variability and overestimation of calorie requirements for weight loss in dogs and cats.
Cost also varied widely among the diets in the study on both a weight (per kilogram) and energy (per 100 kcal) basis. There was no significant difference in cost between diets with and without specific feeding directions for weight loss, but there was a > 8-fold difference in cost within each diet category. Part of this was attributable to a higher cost for canned diets, compared with the cost for dry diets, which is not unique to weight-loss diets (ie, canned diets typically are more expensive than dry diets). However, there also was large variation within each type of diet. Median recommended calorie intake for both dogs and cats was approximately 1.0 × RER for current body weight (ie, 1.0 × RER for dogs and 0.95 × RER for cats). If a client were to feed RER for current weight in a standard 36.4-kg dog (1,037 kcal/d), median cost for the diets in this study would be $1.24/d (range, $0.42/d to $9.23/d), depending on the diet selected. For a standard 5.5-kg cat at RER (251 kcal/d), median cost would be $0.43/d (range, $0.10/d to $2.79/d). However, to achieve effective weight loss, additional calorie restriction below RER for current body weight would likely be necessary, so the total cost might be less (although with a wide variation among diets).
It should be mentioned that diet selection and control of calories from the diet are important, but they are not the sole components for a successful weight loss program. Animals vary in their energy requirements, and it is always necessary to adjust feeding recommendations for each animal. Weight loss can only be achieved if lifestyle changes also are made, such as an increase in physical activity (when possible), control of other calorie sources (eg, treats and table scraps), and detection and treatment of any medical conditions that could compound the inability to lose weight. However, because pet food is a major source of calories for most dogs and cats, it is a key component for successful weight loss. Therefore, without objective calorie information on labels and specific veterinary guidance, it is unrealistic to expect owners to be able to appropriately assess their pet's calorie intake or to feed pets to achieve and maintain optimal body weight.
Pet food companies could assist in improving pet health by developing foods with lower caloric density on a volume basis, making more accurate feeding directions (based on optimal weight and not on current weight), and providing calorie information on labels of all pet foods and treats, which would aid pet owners and veterinarians when objectively evaluating an important consideration in selecting pet food.
Veterinarians can play a critical role in optimal pet health by educating owners on selection of an appropriate pet food, making specific recommendations for the amount to feed, and most importantly, educating owners on assessing body condition of their pets and the serious health conditions that can result from or be exacerbated by obesity of their pets.
ABBREVIATIONS
| AAFCO | Association of American Feed Control Officials |
| MER | Maintenance energy requirement |
| RER | Resting energy requirement |
Systat 11.0, SPSS, Chicago, Ill.
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