Waist, measuring tape, weight loss, low GI diet.

A high-carbohydrate diet focusing on healthy carbs may be the key to sustained weight loss, according to a new study.

We've seen them all: caveman, Atkins, cabbage soup, white, coconut water, raw. When it comes to diets, there are few nutritional stones (and marketing fads) that have been left unturned.

But the answer to long-lasting weight loss may in fact be rather more level-headed in its approach - and focuses on the concept that not all calories are created equal.

A new Journal of the American Medical Association study "challenges nutritional dogma", says co-author Dr David Ludwig, pointing to ample good quality carbohydrates, rather than low-fat or low-carbs plans, as a solution to maintaining a balanced weight without any side-effects.

A low-glycemic index approach, combining fruits, vegetables, nuts and wholegrains, which release sugars into the bloodstream slowly, saw sustained weight loss and reductions in cholesterol levels and diabetes and heart disease markers.

It also saw a high energy expenditure, or the number of calories burnt by resting and through activity - levels of which are known to decrease through dieting and so lead to rapid weight gain after shedding kilos.

Conversely, a low-fat diet did not lead to long-term weight loss.

Researchers at the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital looked at energy expenditure and the blood's hormone and fat levels of a group of 21 participants when on three different diets.

A low-glycemic index diet calorie intake was limited to 40 per cent carbohydrate, 40 per cent fat and 20 per cent protein.

A low-fat diet saw calories from fat limted to 20 per cent and an Atkins-style low-carbohydrate diet saw calories from carbs limited to just 10 per cent.

Breaking regular approaches to diet studies, researchers prepared food for study participants, all aged between 18 and 40, so that meals were monitered closely and mostly eaten at the hospital.

Having lost weight on a previous control diet, participants then given the low-GI diet maintained their new weights and energy expenditure levels.

Not only did they burn an average of 150 calories more than those on the low-fat diet, but hormone and fat levels were positively affected.

Dr Ludwig said that energy expenditure-wise, the low-fat diet had the worst outcome, with associated increases in some fats and declines in "good" cholesterols.

He told the Wall Street Journal that dieters "should avoid severely restricting any major nutrient and focus on the quality of the nutrient." The Mediterranean-style low-GI diet is "ideal" according to the Massachusetts-based team.

In that vein, the low-carbohydrate diet - similar to the Atkins diet that was re-invigorated after the publication of 2002 hit diet book, Dr Atkins' New Diet Revolution - saw an initial high energy use, burning 300 calories more than the low-fat diet.

But with it, found the scientists, came negative side-effects that outweighed any benefit of the calorie use, namely peaks in stress hormone, cortisol, and raised inflammation levels linked to heart disease and diabetes.

Challenging notions that calorie loss equals weight loss, the study may also go some way in explaining previous findings that only one in six overweight people will maintain even 10 per cent of their weight loss in the long term.