Going on a diet is unlikely to lead to long-term weight loss, according to a new study.

Researchers in California found people typically lose between five and 10% of their starting weight during the first six months of a diet. But the study found between a third and two-thirds of people who went on diets regained more weight than they had lost, within four or five years.

The study was carried out by researchers at UCLA, California’s biggest university. The report found that the majority of people regained all the weight, plus more. Sustained weight loss was found in only a small minority of participants, while complete loss regain was found in the majority. Diets do not lead to sustained weight loss or health benefits for the majority of people.

Researchers analysed 31 long-term studies that followed participants for two to five years. They concluded that most of them would have been better off not going on the diet at all. Their weight would have been pretty much the same, and their bodies would not suffer the wear and tear of losing weight and gaining it all back.

Four children whose brains and mental abilities were suddenly transformed after they took a simple dietary supplement have astonished scientists.

Scans showed their brains underwent three years’ of development in just three months. At the same time they displayed remarkable improvements in tests of reading, concentration, problem-solving and memory. One boy who previously scorned books and was hooked on TV developed a love of reading and declared he was “bored” of television.

The three boys and one girl, aged between eight and 13, were taking part in a pilot study looking at the effects of diet on developing young brains. Scientists believe the results are powerful evidence of the harm “junk food” is doing to Britain’s children.

The children were given a supplement containing a combination of omega-3 and omega-6 essential fatty acids, and encouraged to cut down on fatty snacks and fizzy drinks and be more active. At the end, they underwent brain scans at St George’s Hospital, London, in a machine that can detect a key biochemical indicator of brain development called NAA (N-Acetylaspartate).

Higher levels of NAA correspond to more nerve fibres growing in the brain. Researchers from Imperial College London claimed that the results were astonishing and that they saw as much growth in NAA in three months as you would normally see in three years.

Just fifteen minutes of brisk activity a day could halve the risk of children becoming obese, say researchers. They discovered a small amount of moderate exercise could have far reaching benefits.

The number of fat children has doubled in ten years with one in four aged 11-15 now classified as obese. Almost half of girls are obese or overweight. Junk food, sedentary lifestyles and the couch potato use of TV as an ‘electronic babysitter’ are blamed for creating the problem. At the same time, levels of inactivity have soared as many children no longer take part in competitive sports at school and playing fields have been sold off.

The Bristol University Children of the 90s research project monitored 5,500 12-year-olds. It found 15 minutes of extra activity per day cut the risk of becoming obese by more than half in boys and at least 40 per cent in girls.

This study provides some of the first robust evidence on the link between physical activity and obesity in children. We know that diet is important – but what this research tells us is that we mustn’t forget about activity. It’s surprising how even small amounts of exercise appear to have dramatic results. In the latest study, published in March 2007 in the journal PLoS (Public Library of Science) Medicine, children were given a monitor to wear for up to a week which kept track of their movements. The research showed that the level of intensity of the activity was critical.

Moderate to vigorous activity was much more effective, which means exercise that makes a child get a little out of breath, but the study also indicated that it may be something quite small that makes a difference – such as how children get to school, whether they are walking, cycling or being driven in a car.