A study comparing four popular diet plans found that people who stay on any of the diets for a year lose some weight and lower their risk of heart disease.

The study found the average weight loss for participants in the four diet plans – Atkins, Dean Ornish, the Zone and Weight Watchers – was about five per cent of their body weight, far less than most dieters hope for.

Even with that modest weight loss, though, all the diets cut the risk of heart disease by seven to 15 per cent.

However, at least a third – and up to a half – of the participants in the study dropped out of their diets before the year was over.

The researchers said none of the diets was any better than the others, and they all likely worked by the same mechanism: getting people to eat fewer calories.

The Atkins diet recommends very low carbohydrate intake, but relatively high fat consumption. The Ornish diet is a low-fat, high-carbohydrate vegetarian diet.

The Weight Watchers diet recommends low fat and moderate calorie consumption, while the Zone diet is based on how different foods affect blood sugar levels.

The study, led by researchers at Tufts University in Boston, was presented at the annual meeting of the Amercian Heart Association in Orlando, Fla.

The study followed 160 overweight and obese men and women, ranging in age from 22 to 72. They were randomly assigned to one of the four diets for a year.

The participants were each given a book describing their diet program and researchers periodically measured their body weight and took blood and urine samples.

About half of the participants following the Atkins and Ornish diets, considered the more extreme plans, dropped out before the year was over.

About a third of the people following Weight Watchers and the Zone dropped out.

But those who completed the year on their diets lost an average of 5 per cent of their body weight.

The modest weight loss brought with it significant health benefits, the researchers found.

Risk of heart disease dropped seven per cent for the Ornish group, 11 per cent on the Zone, 12 per cent for Atkins and 15 per cent for those on the Weight Watchers plan.

The researchers found no adverse effects for any of the diets.

Statistics Canada says about 48 per cent of Canadians are overweight.