What causes obesity?

Everyone reading will know the answer to this question – an individual piles on the pounds if they eat more calories in food than they burn off each day.

Because of that, veterinary research has focussed on how owners manage their dogs.  Unsurprisingly, dogs offered human food, or calorie dense food, or fed more frequently are prone to obesity, as are those that get less exercise.

But… breed, age and sex are also affect how likely a dog is to become obese – and remain there even when management factors are taken into account.  That means their effect is genuine and independent of owners.

So, whilst the physics of the energy-in vs energy-out dogma is of course true, it is overly simplistic to dismiss the role of other biology in why animals get fat.

When getting fat was a good thing

Long term obesity is a problem for the body but remember: there are good physiological reasons for storing excess energy as fat.  Fat is an energy reserve that the body can use when food is scarce.  That the majority of evolution has occurred in a resource-poor environment, so it makes sense that the body is set up to lay down fat in times of plenty to prepare for times when food is unavailable.

In recent years, the lifestyle of pet dogs (as of humans) has changed such that most now live relatively inactive lives and have ongoing access to calorie dense food.  Most dogs now live indoors, too, and don’t use so much energy to keep warm.

So, the body is evolved to cope with food being scarce and hasn’t adapted along with dogs’ lives and environments.  It is that clash which underlies the obesity epidemic we see in our pets.

But what regulates energy intake?

Why won’t dogs just keep eating forever?  Or just stop when they’ve had enough to get through the day?  The graphic below summarises the ways in which appetite is regulated.


The diagram shows how messages from the gut and blood about energy status are received by the brain.  Short term messages send information about meals (or lack of meals).  Longer term messages send information about how much energy the body has stored as fat.  An area of the brain called the hypothalamus integrates the information to produce the sensations of hunger or fullness that we are aware of.

You can read more about the science in articles you can find on the links page.

Go on to the next section to learn about how our (dogs’) genes affect the likelihood of any one person becoming obese.