‘I am inclined to resent the wide publicity recently bestowed upon a certain [cat which] has achieved notoriety by measuring 33 inches round the waist and weighing just over 2 stone. That is a good deal of cat; about three times too much, to be perfectly frank.’
‘Far be it from me to sneer; obesity, whether in beasts or baronets is a matter for pity, not for mirth. When I look at what is styled as a “pet dog”, wheezy and corpulent, his capricious appetite tempted with dainty food, his healthy canine instincts destroyed by wicked or unnatural pampering, I wonder that its owner is not ashamed.’
Not my words, but those of a certain KRG Browne writing in the Daily Mail in 1934, and secondly ‘A lady’, so upset about pampered pooches she wrote to the Nottingham Post in 1881. Not much has changed; there has been much publicity about pet and human obesity over recent years. But does the reality match the hype?
For the first time in human history, there are more overweight and obese people on the planet than people suffering from malnutrition. Given the high burden of obesity-related disease in humans, it’s no wonder human obesity is big news.
IS OBESITY SUCH A BIG DEAL IN COMPANION ANIMALS?
Estimates suggest at least a third of adult dogs and cats are overweight. Obese dogs die sooner and have a higher incidence of orthopaedic, cardiac, respiratory, urinary, reproductive and dermatological disorders, as well as of some cancers and anaesthetic complications. In cats, the health risks of obesity are also well established; diabetes, hepatic lipidosis, urinary tract disease, lameness and dermatopathies predominate. As such, there is little doubt obesity represents a significant health and welfare problem for pet dogs and cats.
Although there is much overlap of obesity-associated disease between dogs, cats and humans, there are also notable differences. For instance, feline diabetes is predominantly a consequence of obesity-related insulin resistance, as in humans. That contrasts with the picture in dogs where, although there is mounting evidence that obesity is associated with insulin resistance, the links between obesity and diabetes are not well established.
Perhaps the most striking interspecies difference relates to cardiovascular disease. Atherosclerosis and stroke, which are such common sequelae tohuman obesity, are almost unheard of in veterinary species, despite the fact that insulin resistance, hyperglycaemia and dyslipidaemia occur in obese dogs and cats. It is not clear whether this reflects a fundamental resistance to atherosclerosis, or is simply because they don’t live with obesity for so many years, meaning vascular lesions don’t have time to develop.
Other comparisons ripe for further investigation include the parallels between feline hepatic lipidosis and human non-alcoholic fatty liver disease, and the reason why dogs don’t develop obesity-associated diabetes.
INDULGENT OWNERS OR HARD WIRED BIOLOGY?
With calorie-dense food increasingly affordable and sedentary lifestyles more common – for both humans and pets – it is no surprise that obesity is increasing. But dismissing human or animal obesity as a straightforward consequence of gluttony and laziness doesn’t hold up to scrutiny under the spotlight shone by mounting evidence that appetite and energy expenditure are closely regulated homeostatic mechanisms, subject to influence by genetic and environmental factors.
Obesity is highly heritable in humans and strong breed predispositions suggest genetics are equally important in dogs. Labradors regularly top the obesity tables. Are we really to believe Labrador owners are so much more exercise-averse and indulgent with food that their dogs develop obesity, while owners of borzois and pointers (both commonly lean breeds) are a virtuous bunch who carefully regulate their dogs’ weight? No – it is far more plausible that the tendency to eat to excess is hard wired in Labrador biology.
It was to investigate this that I set up the GOdogs project, collecting a cohort of Labradors to study the genetics of obesity and appetite in the breed. If you are a Labrador fan, do you know any overweight, highly food-motivated Labradors or – and these are the dogs which are particularly hard to track down – lean Labradors who are not highly food-motivated? If so, please do get in touch via www.GOdogs.org.uk.
Participating dogs donate a saliva sample and must be weighed and condition-scored by a vet or vet nurse. Exciting preliminary findings suggest that a mutation in a gene known to be important in human appetite regulation is a major modifier of appetite and obesity in Labradors – keep your eyes out for future results!
Written by Eleanor Raffan, Postdoctoral Research Associate, University of Cambridge
Originally published in The Endocrinologist