How Water Can Help Your Cat Lose Weight - and Keep It Off

Estimates of obesity in cats are as high as 50 percent of all cats. An often cited reason for this health problem is the increasing caloric density of food. Cat foods, especially the dry types, have become more and more calorie dense, often exceeding 375-400 calories per cup. The average cat only needs about 200-250 calories per day!

As most cats are fed "free-choice," it is no wonder there are so many fat cats. Recent studies in cats have shown that increasing the water content of food, wet and dry, has shown to be effective in weight loss and weight maintenance post dieting. 

Weight Loss for Cats

In a 2011 University of California, Davis study, researchers alternately fed cats a canned diet with water added and a freeze dried version of the same canned diet with a low volume of water. Other than the moisture content the diets were nutritionally identical. The cats were fed free choice. Although cats ate significantly more of the high water diet, they consumed 86 fewer total calories per day than when fed the low water content diet. This means the cats voluntarily ate only 75 percent of their daily caloric needs. It is no surprise that the cats lost weight when eating the high water diet.

Weight Maintenance for Cats

As discussed in earlier blogs, dieting results in a host of metabolic changes that makes the body more efficient with calories. Resuming the pre-diet calorie intake after dieting will result in significant weight regain.

Researchers in England found that adding water to dry food could decrease the amount of weight regain in cats that had dieted. Two groups of cats were dieted with dry food containing 20 percent water to target weight and then offered either the same dry food without water added or the dry food that contained 40 percent water free choice. In this study both groups consumed the same number of calories post-diet, but the cats receiving the 40 percent water diet regained less weight than those fed the dry food without water. Further investigation found that the cats on the high water diets had higher levels of voluntary physical activity.

What Do These Studies Tell Us?

Studies in cats and dogs have confirmed calorie dilution using fiber aid weight loss and weight maintenance. Both of these studies confirm water as a viable substitute for fiber in weight loss with either canned or dry food.  More study is needed to explain how water helps with weight regain. In the English study the addition of water did not decrease the calorie consumption of the cats despite diluting the calories. The decrease in weight regain would need to be attributed to the increased exercise or some other, yet unidentified effect of the added water. All in all, I think the research is interesting for its implications for overweight cats.

One Reservation  

In the English study the researchers used regular dry food. Because it was a laboratory situation with a short experimental duration, nutritional adequacy of such an approach was probably not significant. However, dieting an overweight cat can take months to over a year. Using regular food for such an extended period of time could be nutritionally detrimental to the dieting cat. As you all know, I constantly emphasize the need for foods that are formulated for dieting to avoid malnutrition. Few nutritional deficiencies have immediate medical symptoms and it can take years to discover the effects of an inadequate diet. Adding water to properly fortified weight loss/weight maintenance diets (veterinary or homemade) is less likely to result in nutritional deficiencies. Consult your veterinarian before trying the "water diet."

Dr. Ken Tudor

Image: Jorg Hackemann / Shutterstock

Last reviewed on September 16, 2015