Ask The Doctor – Carbs and Metabolism in Cats


Do carbs make cats fat?
Q I am a long-time subscriber to Catnip, and a volunteer for feline rescue groups in my area. A large female recently came to us at a little over twenty pounds, and was described by our vet as a food-grazer. For the past three weeks under our care, she has been receiving one-quarter cup twice daily of a veterinarian-recommended weight reduction food, and she has lost just under one pound.

But I have a metabolic question about “portly” cats. Compared to “normal” cats, do the digestive tracts of fat cats contain bacteria that digest carbs? Might this be the reason why they can gain weight on high carb diets? Has there been any research on the comparative gut flora of these two categories of cats?
Dr. Eleanor Saboski

A Dear Dr. Saboski: While many people believe that high carbohydrate diets lead to obesity in cats, the actual scientific evidence suggests that high fat diets (which are frequently lower in carbohydrate) are more likely to lead to obesity than high carbohydrate diets. No studies have linked high carbohydrate diets to obesity in cats. My focus when looking for a weight loss diet for cats is that it be high in protein, low in calories and high in nutrients per calorie.

In order to keep the calories low, most therapeutic diets are lower in fat — which means that by default they are higher in carbohydrates. There is no evidence that this is harmful, and many cats do very well on these types of diets and do lose weight when owners are diligent about weighing them and adjusting intake. Unfortunately, most over-the-counter diets do not have adequate nutrients to allow low calorie amounts to be fed without leading to suboptimal nutrient levels. These diets could lead to nutrient deficiencies if the levels are low enough and they are fed long enough.

To address your other question, yes, there are differences in gut flora between overweight cats and thin cats, but I’m unaware of anything related to carbohydrate metabolism. And as I mentioned above, the scientific data do not support the commonly repeated belief that high carbohydrate diets make cats fat.
Cailin Heinze, VMD, MS, DACVN
Assistant Professor of Nutrition
Cummings School of Veterinary
Medicine at Tufts University


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