In a new article in Nature Reviews Endocrinology, scientists from the University of Liverpool argue that anti-obesity drugs fail to provide lasting health benefits because they tackle the biological consequences of obesity, not the important psychological causes of overconsumption.

Anti-obesity drug developers focus primarily on weight loss as their end goal, and do not take into consideration the motivational and behavioral factors that most commonly cause obesity. Obesity typically results from eating too much food combined with too sedentary a lifestyle.

However, obese people may also have a complicated psychological relationship with food that makes it difficult for them to control their appetite sufficiently to manage their weight.

"As psychological factors are critical to the development of obesity, drug companies should take them into consideration when designing new drug therapies. We've learned a great deal about the neurochemical systems that govern processes like the wanting and liking of food, and it's time to exploit that knowledge to help people manage their eating behavior," said Dr Jason Halford, Reader in Appetite and Obesity at the University of Liverpool

Anti-obesity drugs can work in different ways; for example, by suppressing appetite, altering metabolism or inhibiting the absorption of calories. There have, however, been serious concerns over the safety of the most commonly prescribed drugs, leading to the recent withdrawal of the European market leaders Sibutramine (Reductil, Meridia) and Rimonabant (Accomplia). As a consequence of these setbacks, there are few anti-obesity drugs in development.

There are motivational, emotional and behavioral traits which are common to the obese. Typically, obese people have a heightened desire to eat, which is easily provoked by environmental factors such as food adverts. They display a pre-occupation with food and have a heightened preference for high fat and high sugar foods. Obese people also tend to eating faster and take larger mouthfuls which together result in them eating bigger meals.

However, despite eating larger than normal portions, obese people are less likely to feel full after eating, partly because of the energy-dense foods they prefer have a reduced impact on gastrointestinal hormone signals that help promote feelings of satisfaction and fullness. Consequently, there are a number of reasons why obese people have enduring, and easily provoked, feelings of excessive hunger which culminate in overconsumption.

"Novel, effective anti-obesity treatments must address these different factors. We need to identify drugs that can selectively affect the desire to eat, the enjoyment of eating, fullness and satisfaction. Interventions designed specifically to modulate these processes could help reduce the aversive experience of dieting, and maximize an individual's capacity to successfully gain control over their appetite," said Professor Tim Kirkham, an authority on the biopsychology of appetite at the University of Liverpool.

"Currently, we know little about the behavioural effects of anti-obesity drugs under development, and so we have little indication whether these new treatment address the underlying causes of obesity."

Citation: Halford et al., 'Pharmacological management of appetite expression in obesity', Nature Reviews Endocrinology March 2010; doi:10.1038/nrendo.2010.19 Review