We are excited to announce a new publication! Dr. Caitlin Grant and colleagues recently published their new article “Ex vivo energy restriction in obese cats reveals more amino acids and vitamin intakes below recommendations with over-the-counter compared to veterinary weight-loss diets” in American Journal of Veterinary Research. Read on for a short summary of their research and findings below.
Objective
Obesity is the most common nutritional disorder for cats, affecting up to 63% of the population in North America, making it essential to tackle this veterinary challenge. Obesity in cats is linked to a host of comorbidities, including diabetes mellitus, osteoarthritis, and hepatic lipidosis. Energy restriction, also known as calorie restriction, remains the main method for weight loss in cats.
In practice, veterinarians often recommend reducing the amount of food fed to induce weight loss, but this approach assumes that the diet remains nutritionally complete even at lower feeding volumes. However, this assumption may not hold true, especially when over-the-counter diets are used instead of veterinary-formulated weight-loss diets.
The research team sought to evaluate whether energy restriction using different types of commercial diets could inadvertently lead to nutrient intakes lower than recommended, potentially risking nutrient deficiencies and compromising feline health during weight loss programs.
Therefore, this study used nutrient intake recommendations from the National Research Council to determine the best diet during energy restriction in obese cats by comparing them to the nutrient intake values found in this study.
Materials
Dry adult cat foods, including a veterinary weight-loss diet, an over-the-counter weight management or light-calorie diet, and an over-the-counter maintenance diet from three different manufacturers, resulting in nine total diets, were analyzed to determine the content of amino acids and vitamins in each diet.
We then used data from 16 client-owned obese cats, aged 2-9, and calculated how much food each cat would get under six different calorie-restriction plans. These plans were based on formulas that veterinarians commonly use.
These predictive energy equations were used to calculate the theoretical daily food intake for each cat based on their body weights and target weight loss. We then estimated how much of each essential nutrient—like protein, amino acids, and vitamins—the cats would consume on each diet at each level of calorie restriction.
Finally, we compared the simulated nutrient intakes to the minimum recommended levels set by the National Research Council. This helped to see whether the cats would be getting enough nutrients while eating less food according to the theoretical weight loss plan.
NOTE: This is a theoretical ex vivo energy restriction study, which means the cats were not fed the diets in vivo. Equations were used to calculate nutrient intakes based on the nutrients in the diets and the body weight of the cats.
Findings
- For all diets, energy and protein intake decreased as food restriction increased.
- The veterinary weight loss diets resulted in the highest protein and amino acid intakes and generally maintained essential nutrient levels even under significant caloric restriction. The only consistent deficiency observed was choline.
- When fed to restrict calories, the over-the-counter maintenance diets consistently had intakes of protein, tryptophan and phenylalanine + tyrosine, and choline that were below the National Research Council nutrient intake recommendations.
- The more aggressive the energy restriction, the greater the risk of nutrient deficiencies—especially with non-veterinary diets.
Conclusion
Restricting energy is important for weight loss; however, it is equally important to ensure essential nutrient requirements are met. For example, since cats are carnivores, protein is essential for their function and metabolism. Also, as stated in the results section, choline was low across all diets. This is concerning since choline helps with fat metabolism and transport, ultimately preventing risks of diseases such as hepatic lipidosis, which is a common liver disease in obese cats.
Key Take-Aways
Overall, the veterinary weight loss diets met the majority of NRC recommendations and had higher nutrient intakes compared to the over-the-counter diets.
This study reinforces the importance of using purpose-formulated veterinary weight-loss diets when managing feline obesity. While over-the-counter diets may appear convenient or cost-effective, they often lack the nutrient density required to support cats under caloric restriction for weight loss.
Veterinary professionals should:
- Avoid recommending over-the-counter maintenance or “light” diets for weight loss unless nutrient adequacy under restriction is confirmed.
- Educate pet owners on the risks of nutrient deficiencies when feeding less of a non-therapeutic diet.
- Monitor weight-loss patients closely, not just for weight changes but also for signs of nutrient deficiencies, especially when using non-veterinary diets.
Future Directions
Further studies are needed to determine appropriate nutrient requirements for obese cats and assess the effects of low nutrient intake on health:
Real-Life Validation of Nutrient Deficiencies
This study used theoretical calculations based on diet composition and feeding amounts. Future work should confirm whether these predicted deficiencies occur in vivo in cats during weight-loss programs and assess their clinical impact.
Impact on Health Outcomes
Research is needed to determine how nutrient shortfalls—such as low choline or amino acids—affect metabolic health, muscle mass, and overall well-being during weight loss.
Wet Diets and Mixed Feeding
This study focused on dry diets. Investigating canned diets or mixed feeding strategies could provide a more complete picture of nutrient adequacy under calorie restriction.
Owner Compliance and Feeding Practices
Studies should explore how real-world feeding behaviors (e.g., treats, table scraps, inaccurate measuring) influence nutrient intake and weight-loss success.
Formulation Improvements
There is an opportunity for pet food manufacturers to develop over-the-counter diets with higher nutrient density to reduce the risk of low nutrient intake when fed in restricted amounts.
Funding: This project was funded by the Ontario Veterinary College Pet Trust Funds.
Interested in similar research? Here are some highlights of other studies conducted by our team and blogs on related topics:
- New Publication: Energy Intake Recommendations from Cat Food Labels Sold in Ontario, Canada, Diverge from Predictive Equations for Adult Cat Maintenance
- Serum metabolomics reveals one-carbon metabolism differences between lean and obese cats not affected by L-carnitine or choline supplementation
- A lifelong approach to preventing feline obesity in cats: from kitten to senior
Written By: Breanna Conley, BSc.H (Class of 2026) & Dr. Hannah Godfrey, MSc, PhD
Reviewed By: Dr. Adronie Verbrugghe, DVM, PhD, Dip ECVCN, Associate Professor and Royal Canin Veterinary Diets Endowed Chair in Canine and Feline Clinical Nutrition