Scientists have made sure that most of the overweight people who try to lose weight by cutting calories or exercising will return to their former size．Fewer than 10percent of the 12million British people who go on a diet each year succeed in losing significant amounts of weight and most of those who do put on all weight again within a year． The study of 25，000people provides further evidence of the popularity of‘yo-yo dieting'where people on a diet get into a cycle of losing weight and regaining it．The scientists，from the Medical Research Council's National Survey of Health and Development，have concluded it is better to avoid getting fat at the beginning．They followed 5，362men and women from their birth in 1946and 20，000from birth in 1958，measuring their weight and blood pressure and judging their lifestyles．The researchers found both groups began gaining weight in the 1980s and have steadily increased in size ever since．

Dr Rebecca Hardy，the council's programme leader on body size，said："Once people become overweight，they continue upwards．They hardly ever go back down．They may lose some weight but very few get back to normal．The best policy is to prevent people becoming overweight．For men weight goes up steadily through life．For women it starts slowly and accelerates in the mid-thirties．"

But the findings of the study do not mean dieting is pointless，as eating less and taking more exercise can increase fitness and lower blood pressure．In 2009，a quarter of adults and 14percent of children were obese（过度肥胖的），according to the Department of Health's latest Health Survey for England．It has been predicted that 60percent of us will be obese by 2050，leading to even more cases of diabetes，heart disease and cancer．Experts said we are programmed to put on weight rather than lose it．Dieting can make this tendency worse as decreasing calorie intake causes the body to go into starvation mode and reduce the amount of energy it naturally expends，maki