The first few pounds may be the hardest to shed, but they are by far the best. Obese people only have to lose 5 per cent of their body weight to achieve a marked improvement in their health, from a rejuvenated liver to a lower risk of diabetes, a study suggests.

Researchers said that people struggling with obesity should concentrate on losing a small but feasible amount of weight rather than aim for a dramatic change. Medical academics at the University of Washington in the United States recruited 40 obese people and split them at random into two groups. Half were asked to lose weight by cutting the number of calories they ate, while the other 20 were told to maintain their weight.

In the weight-loss group, 19 of the 20 participants shed 5 per cent of their body mass over the next few months, while nine went on to lose 10 per cent and then 15 per cent. At every milestone the scientists recorded a range of health markers including cholesterol, blood sugar and insulin sensitivity, a key measure of the risk of diabetes.

The results, published yesterday in the journal Cell Metabolism, show that the initial burst of weight loss yielded greater benefits than subsequent phases. Those who hit the 5 per cent target benefited from a substantial drop in body fat, as well as falls in several important risk factors for heart disease, although their cholesterol levels did not change substantially.

Samuel Klein, director of the university’s centre for human nutrition and the lead author, said that the first phase of weight loss delivered “the biggest bang for your buck”.

“The guidelines for treating obesity recommend a 5 to 10 per cent weight loss, but losing 5 per cent of your body weight is much easier than losing 10 per cent,” he said. “So it may make sense for patients to aim at the easier target.

“If you weigh 200lbs, you will be doing yourself a favour if you can lose 10lbs and keep it off. You don’t have to lose 50lbs to get important health benefits.”