The most effective diet for weight loss and cardiovascular health is a high carbohydrate plan based on low glycaemic index (GI) foods, especially for women, according to Australian researchers.
The world's first 12-week trial of its kind compared the relative effects on weight loss and cardiovascular risk of low GI and high-protein diets.
The theory behind low GI diets is that rapidly digested, high GI carbohydrates cause fluctuations in blood glucose and insulin levels, contributing to hunger and preventing the breakdown of fat.
Foods with a low GI include breakfast cereals based on oats, barley and bran, wholegrain and sour dough breads and Basmati or Doongara rice.
Foods with a high GI include potatoes and white bread.
The study by Professor Jennie Brand-Miller and Joanna McMillan-Price of the University of Sydney Human Nutrition Unit, showed that there was no one diet to fit all solutions, although both high protein and low GI diets would help people shed fat.
However, the trial did show that a diet containing low GI carbohydrate significantly reduces the risk of heart disease.
The study enrolled 129 overweight or obese young adults, aged 18-40, and randomly assigned them to one of four reduced calorie, reduced fat diets over a 12-week period.
Two of the diets were high-carbohydrate diets and the other two were high in protein.
One of each category had a high GI and the other had a low GI.
In the two high-carbohydrate diets, lowering the glycaemic index doubled fat loss with this effect strongest in women.
The high-protein, high GI diet was equally effective for fat loss as the high carbohydrate, low GI diet.
But both diets had diverse effects on LDL, or bad cholesterol, with the high protein, high-GI group showing increased levels of bad cholesterol, while there were significant reductions in those on the high carbohydrate, low-GI diet.
However, those on the high-protein, low GI diet did not experience the same rise in total LDL cholesterol suggesting the importance of low GI foods alongside a high meat intake.
"Our findings suggest that dietary glycaemic load, and not just overall energy intake influences weight loss and postprandial glycaemia or blood sugar levels after eating," Ms McMillan-Price said.
"We found that moderate reductions in glycaemic load appear to increase the rate of body fat loss, particularly in women.
"Diets based on low-glycaemic index, whole grain products, tend to be better for the heart, maximising cardiovascular risk reduction - particularly if protein intake is high."
The study is published in the most recent issue of Archives of Internal Medicine.
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