A low-carbohydrate diet is better than a standard, calorie-restricted one for cutting down weight and lowering blood levels of cancer-promoting hormone insulin, a British study has found.

Researchers at Genesis Prevention Centre at University Hospital in South Manchester, found that restricting carbohydrates two days per week may be a better dietary approach for preventing breast cancer and other diseases.

"It is interesting that the diet that only restricts carbohydrates but allows protein and fats is as effective as the calorie-restricted, low-carbohydrate diet," said Michelle Harvie, research dietician at the Genesis Prevention Centre.

Harvie and her colleagues compared three diets during four months for effects on weight loss and blood markers of breast cancer risk among 115 women with a family history of breast cancer.

They randomly assigned patients to one of the following diets: a calorie-restricted, low-carbohydrate diet for two days per week; an "ad lib" low-carbohydrate diet in which patients were permitted to eat unlimited protein and healthy fats, and a standard, calorie-restricted daily Mediterranean diet for seven days per week.

Data revealed that both intermittent, low-carbohydrate diets were superior to the standard, daily Mediterranean diet in reducing weight, body fat and insulin resistance.

Mean reduction in weight and body fat was roughly four kg with the intermittent approaches compared with 2.4 kg with the standard dietary approach.

Insulin resistance reduced by 22 per cent with the restricted low-carbohydrate diet and by 14 per cent with the "ad lib" low-carbohydrate diet compared with 4 per cent with the standard Mediterranean diet.