The fight against pet obesity is not as straightforward as finding a low-calorie or reduced calorie pet food.

A new study from Tufts University’s Cummings School of Veterinary Medicine found a wide variation in calorie density and recommended intake in so-called “low-calorie” dog and cat foods.

The researchers studied nearly 100 commercially available diets with either weight management claims and specific feeding instructions, or foods with implied weight management claims that did not carry feeding instructions. They found that more than half of all foods in the study had a calorie density greater than the Association of American Feed Control Officials (AAFCO) maximum calorie density for light diets.

In the study, the authors point out that pet foods with the words “lite, light, low calorie, less calorie, or reduced calorie” are required to provide calorie content on the label. In addition, foods designated as lite, light or low calorie must, under the AAFCO Model Pet Food Regulations, adhere to maximum kilocalorie per kilogram restrictions, and manufacturers must state the kilocalorie per kilogram content on the food label.

But if a particular food implies that it is for weight control without using one of the specific terms, it is not required to adhere to the AAFCO standards. Some of the marketing claims that imply weight control include: “weight loss, obese prone, to maintain healthy weight, avoid unwanted weight gain, lose excess weight, and reduced calorie,” according to the researchers. This could potentially cause confusion for both consumers and veterinarians when trying to determine an effective weight control diet for a pet.

Some of the key findings:

• Dry dog foods ranged in calorie density from 217-440 kcal/cup
• Dry cat foods ranged in calorie density from 235-480 kcal/cup
• Diets ranged in price from 4 cents/kcal to more than $1.10/kcal
• 58 percent of foods with weight control claims and feeding instructions for weight loss exceeded AAFCO maximum calorie densities for light foods
• 48 percent of foods with weight control claims but without feeding instructions for weight loss exceeded AAFCO maximum calorie densities for light foods

The study concludes that veterinarians should recommend diets for pets based on the needs of the particular animal, and cannot rely solely on the labels on pet foods.

“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,” the authors wrote.

The study was published in the Journal of the American Veterinary Medical Association.