Human medical doctors and researchers have stumbled upon an interesting conundrum they call the obesity paradox. It goes something like this. Obesity is bad. It predisposes us to a wide range of health problems including diabetes and heart disease. But, if a person happens to develop some types of chronic disease (including diabetes and heart disease), obesity actually has a positive effect on survival. In other words, fat people with diabetes and heart disease live longer than people who are underweight or of normal weight with the same diseases.
Nobody has come up with a solid explanation for the obesity paradox in people, probably because like all things medical, obesity is complicated. What seems to make the most sense to me is that once someone gets sick, it can be helpful to have some extra reserves on hand to weather the storm, but genetics, differences in treatment protocols, and other factors may also play a role.
Veterinary researchers have started looking for the obesity paradox in our companion animals. A 2008 study investigated whether the differing survival rates of dogs suffering from heart failure as a result of dilated cardiomyopathy or chronic valvular disease could be explained, at least in part, by their body condition scores and/or changes in body weight after diagnosis. The results showed "survival was significantly different between dogs that gained, lost, or maintained body weight over the course of their disease (P= .04), with dogs that gained weight surviving the longest. BCS [body condition score] and medications were not significantly associated with survival time…"
A 2012 paper examining survival times in cats with heart failure caused by cardiomyopathy found "cats with the lowest and highest body weights had reduced survival times compared with those with body weights in the intermediate ranges, suggesting a U-shaped relationship between body weight and survival." Unlike the situation in dogs, changes in body weight over the course of the study (either gains or losses) did not have a significant impact on the cats’ survival times.
So based on these two studies at least, it looks like there is no obesity paradox as it relates to heart failure in dogs and cats. That doesn’t mean that owners and veterinarians can ignore changes in body weight when a pet becomes sick, however. The canine heart failure study demonstrated that dogs who gained weight while sick survived the longest. The results of the feline study did not bear this out for cats, but I’d be willing to bet that future investigations reverse this finding, if not for heart disease than possibly for other chronic conditions like kidney disease.
What does this mean for owners? If your dog or cat develops heart failure, or any other life threatening chronic disease, maintaining good nutrition is at least as important as any of the drugs you might be giving. Food provides the energy pets needs to counteract the effects of illness, as well as the vitamins, minerals, fatty acids, antioxidants, and other nutrients that can have a positive influence on both the quality and duration of his life.
Dr. Jennifer Coates