Writing in 'Science' magazine, James Hill from the University of Colorado and J. Peters from Procter and Gamble say governments need to take drastic measures to encourage people to exercise more in the battle against obesity.

They say obesity could become a global epidemic and is already at epidemic proportions in the USA. Around 54% of Americans are officially overweight and 22% are obese.

Obesity can lead to major illnesses, like diabetes and coronary heart disease.

Partnership

Because it is difficult to treat, scientists believe prevention is the best way forward. Hill and Peters recommend a partnership approach between big business, health and education, similar to that used for other health problems like AIDS and smoking.

Fit people should get perks, say scientists

They say children should be encouraged to do regular exercise at school and teachers should make exercise as much fun as sedentary pastimes like playing computer games.

They add that governments should provide incentives for the food and agriculture industries to reduce portion sizes and make low-fat food more easily available.

And they argue against forcing children to clean their plates, saying young people generally know their food limits and eat according to the energy they expend.

'Fat' environment

Although they say that genetic factors can determine individuals' propensity to get fat on a certain diet, they believe that the underlying problem is more general: high-fat food is becoming too easily available and people are doing too little exercise.