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The anatomy, and neurobiology, of appetite

What actually is appetite? And why do some people become severely obese while others are able to maintain a stable weight without effort?

The Wellcome Trust talk to researchers in the field to digest four major influences on our appetite in a special feature piece, an exert of which is below:

Eat to live: the act appears simple at first glance. The digestive system runs from the mouth, down the oesophagus to our stomach and intestines, where food is absorbed for energy or the waste material passed.

But a look around at the various body shapes, different palates and increasing waistlines of the global population implies that something much more subtle is at work. According to WHO figures, approximately 1.6 billion adults and 20 million children were overweight globally in 2005. By 2015, approximately 2.3 billion adults will be overweight and more than 700 million will be obese, according to projections. And while the problem has a focal point in high-income countries, low and middle-income countries are beginning to experience the crisis as well.

"We have a sophisticated system for controlling our appetite and our weight,"

explains Cambridge Neuroscientist Dr Sadaf Farooqi, pictured left, a Wellcome Trust Senior Clinical Fellow at the University of Cambridge,

"and appetite is really the body's system for what we eat and how we eat. What we prefer to eat."

This sophisticated system involves not only the gut but also the brain and is influenced by our genetic make-up and environment. The way in which these parts work, separately and together, and how to optimise them for an ideal appetite is the focus of intense research by Farooqi and other researchers.

"The control centre for appetite is the brain", explains Farooqi. "It will govern how you eat and how much energy you burn up, on a day-to-day basis and over a long period of time. The brain pulls in things you see, smell, taste, hear."

The brain, like the gut, produces its own hormones both to encourage and inhibit appetite. The hormones MCH and NPY, which are produced by the hypothalamus, can block pain signals, such as a feeling of fullness, and encourage eating. The hypothalamus also secretes melanocyte-stimulating hormones, which can slow down appetite.

But there is still much to understand about the brain, as it is not simply a straightforward mechanism for passing signals along.

"Our brain also pulls in things you've learnt about to determine how we eat and what we eat,"

explains Farooqi. So personal memories of food, both good and bad, and emotions around eating that are individual to a person, are stored in the brain. How these influences affect appetite are yet to be completely understood.

To access the Wellcome Trust Feature News article with Stephen O'Rahilly, Sadaf Farooqi and Stephen Bloom talking about their work on obesity and appetite control, including a video entitled: Hungry for Progress: Appetite, genes and drugs please click here.

Posted on 30/04/2010