Obesity is the number one nutritional disorder in pets in the western world. Twenty five percent of cats seen by veterinarians
in the USA and Canada are overweight or obese. Cats are no different than the rest of us, in that, over-consumption of calories
results in storage and is manifested as excessive body fat. In optimal condition, cats should carry 15-20% body fat.
In 1998, Scarlett and Donoghue1 looked at diet and obesity in cats. Using multivariate statistical analysis controlled for age, they showed that obesity
is a risk factor for diabetes mellitus, skin problems, hepatic lipidosis, and lameness. A more general look at the consequences
of obesity or a chronic overweight state adds the additional risks in other species as well as the cat: hyperlipidemia, insulin
resistance, glucose intolerance, feline lower urinary tract disease, anaesthetic complications, dyspnea, Pickwickian syndrome,
exercise intolerance, heat intolerance, impaired immune function, exacerbation of degenerative joint disorders and dermatological
Interestingly, mixed breed cats were found to be at higher risk for becoming overweight than purebreds. This might be genetic,
but husbandry and awareness of the cat may play a role. Because we confine cats indoors, feed them highly palatable, calorie-dense
diets which they do not have to work for, and leave them alone many hours a day, possibly resulting in boredom, our cats are
prone to consuming too many calories.
Neutering has been shown to reduce the energy requirements (resting metabolic rate) of cats by 20-25%.A link has been suggested
between weight and fat gain following gonadectomy and serum leptin levels. It has also been shown that increased leptin levels
may contribute to the decreased insulin sensitivity (resistance) seen in overweight cats. In fact, further work has indicated
that insulin resistance and glucose intolerance develop in obese cats and that this occurs at an increased incidence in male
cats; interestingly, male cats are at increased risk for developing diabetes mellitus.
It is important, therefore, that we counsel our clients to change to an adult formulation and to watch carefully for weight
gain and adjust caloric intake accordingly. Ten extra pieces of an average formulation kibble/day above a cat's energy needs
can result in a weight gain of one pound of body fat in one year!
Cats reach their adult weight at about 12 months of age. This can be used as a guide to determine if a cat is becoming overweight.
As many of us know, it is easier to guard against weight gain than it is to lose weight.
The longer a cat (or person) is overweight, the greater the chance that one of the negative consequences of obesity will occur.
This is similar to driving over the speed limit; the longer one does this, the greater likelihood of getting caught.
What specifics do we need to consider when addressing obesity because they are peculiar to cats? Cats weren't designed
to utilize carbohydrates. As obligate carnivores, they have a smaller stomach and shorter intestinal tract relative to their
body size when compared to omnivores or herbivores.
This is a reflection of their need for frequent meals. Their normal diet of small prey provides them with protein and fat.
They lack glucokinase as a core enzyme in hepatic glucose metabolism. Of further note regarding the feline evolutionary disregard
for carbohydrates, is the finding that cats lack salivary amylase and have only 5% of the pancreatic amylase activity and
10% of intestinal amylase activity of dogs.
Cats derive less energy per gram of carbohydrate than humans or dogs do. Cats have a vestigial cecum and a short colon which
limits their ability to use poorly digestible starches and fibers through microbial fermentation seen in the large bowel of
omnivores and herbivores.
This does not, however, imply that cats cannot use carbohydrates. They can use carbohydrates quite efficiently despite a lack
of a dietary requirement for this energy source. Carbohydrates are a good energy source and have been shown to be necessary
for lactating queens. If there is too much lactose or other sugars in the diet, then bloating, diarrhea and flatulence may
These points may be of clinical significance when considering the role that dry formulations (which contain more carbohydrate
than other formulations) play in the way we feed cats. We really don't know what impact long term carbohydrate intake plays
in predisposing cats to obesity and diabetes mellitus. Research out of Australia as well as the United States, The research
is ongoing and hopefully we will have some answers in a few years.