Fatty acids found in fish are known to slow ageing in the human brain but new research by an Australian team of scientists has now discovered that overweight people can also benefit from fish oils, as long as they do a little exercise.

Daily doses of oil containing Omega-3 fatty acids, combined with moderate exercise like walking for three quarters of an hour, can result in significant weight loss, the researchers have found.

But taking the oils without exercise, or exercising without taking oils, does not result in any weight loss, the team from the University of South Australiahas found.

In simple terms, fish oil increases the elasticity of blood vessel walls and improves the flow of blood to muscles during exercises.

"When we divided up a number of people in our research programme, we found that those taking fish oil combined with exercise lost significantly more fat mass than any other group in the study," said the research leader, Professor Peter Howe.

Sixty eight overweight-to-obese adults at risk of coronary disease took part in the 12-week trial overseen by PhD student Miss Alison Hill.

They were divided into four - a group taking fish oil and exercise, another taking just fish oil, a third group taking sunflower oil without exercise and a fourth being asked to combine sunflower oil and exercise.

As well as being overweight, the participants had risk factors for what is known as 'metabolic syndrome'- a cluster of symptoms associated with obesity and includes elevated blood pressure.

Other risk factors in the study group were high blood triglycerides - a type of fat which is an indication of future heart and arterial disease -- and insulin resistance or heightened insulin levels, which are precursors to diabetes.

"The consequences of metabolic syndrome are type two diabetes and cardiovascular disease, which is why we're so concerned about the looming epidemic of obesity," said Professor Howard.

The clear winners in the study were those in the group who were given small daily doses of fish oil and who walked or ran for 45 minutes three times a week. They lost an average of 4.5lb over the three months.

The group which took the sunflower oil, which does not contain Omega-3 fatty acids, but who exercised, did not lose any weight. The two groups which did no exercise including those on fish oil - also lost no weight.

"If you take the Omega-3 each day and exercise moderately, our studies show your weight will drop," said Miss Hill. "We were very surprised to see it was so effective, especially since these people were still eating whatever they wanted."

Professor Howard said: "Seeing the impact on body shape and body composition of these participants has been the most exciting outcome of the research."