Official: losing weight really is an uphill task

It is one of life's injustices that eating less can mean gaining more. Those who eat moderately and exercise regularly all their lives are still prone to middle age spread, scientists have found.

The male waist - and the female rear - tend to expand with each passing decade, even when the quantity of calories consumed and exercise taken remains unchanged.

Figures confirming that obesity is now one of the western world's greatest health problems were published yesterday, as scientists said that the only hope of maintaining a svelte figure throughout life is to add a mile or two to the jogging circuit and cut a chocolate bar or two from the diet each year.

Obesity has doubled in the UK in the last ten years to 15 per cent and more than half the population is now classified as overweight. By the year 2005, more than one in five of those over 25 and one in four of those over 45 will be obese, according to the report by the market research organisation Datamonitor.

A US study of nearly 4,700 men aged under 50 who jogged regularly found that, although leaner than sedentary men, they gained weight and girth over the years at almost the same rate regardless of the miles run per week. An average 6 ft man gained about 3.3 lbs and about threequarters of an inch round the waist for each decade of life regardless of whether he ran less than 10 miles or more than 40 miles a week.

Paul Williams, of the Lawrence Berkely National Laboratory in California who led the research, said waist line expansion appeared to be a force of nature which occurred independently of the decline in physical activity associated with ageing. "Instead of doing less, as we get older we should be doing more," he said.

The findings, published in the American Journal of Clinical Nutrition, are part of a larger study of 55,000 runners. They suggest that to keep weight gain to a minimum, joggers need to run an extra 1.4 miles a week each year, or 14 miles extra each decade. Mr Williams, a statistician, admitted: "It is a little ambitious. You have to be practical."

Dr Nicholas Peirce, research fellow in obesity and exercise at Queen's Medical Centre, Nottingham, said: "If you eat exactly the same and do exactly the same amount of exercise throughout life, you will tend to put on weight. But it is a dangerous assumption to then say that exercise is no use in curbing weight. If you take two groups of people evenly matched in every respect except the amount of exercise they take, the ones who do less will on average be larger."

People need fewer calories as they age because of hormonal changes, reduced metabolism and the decline in muscle bulk which is one of the major determinants of the amount of energy spent. The distribution of fat on the body also changes with advancing years with more deposited round the abdomen in men and on the hips and thighs in women. The result of these changes is that a ten mile jog by a 70-year-old, although physically more demanding than for a 20-year-old, burns less energy because there is less muscle to power. To achieve the same weight reducing effect the 70-year-old would have to jog many miles further.

The Datamonitor survey says there is a vast potential market for anti- obesity drugs now under development which are currently used to treat only 5 per cent of the obese. In the US alone, there are an estimated 22 million obese adults which is expected to grow to 26 million by 2005.

However the report says that public education aimed at diet and exercise has a far better chance of curbing growing girths.