If you have to choose between bread or butter in your diet, which should you go for? The right answer is the fat, according to a recent study in the Annals of Internal Medicine. A low-carbohydrate diet may actually be better for weight loss than a traditional low-fat diet, and have the added bonus of reducing the risk of heart disease. In the study, 148 obese adults were told either to cut down on saturated fats (meat, whole milk and butter) or high-carb foods (white bread, sugary cereals and other processed foods). The groups didn’t have calorie restrictions, but both reported cutting back by between 500 and 700 calories a day.

After a year, the low-carb group had lost an average of 5.4kg (12lb) compared with 1.8kg (4lb) in the low-fat group. They also, more unexpectedly, had better cholesterol levels, a greater reduction in body fat and a higher proportion of lean muscle mass. As often happens in such diets, the low-carb group were found to have replaced the calories they would usually consume in sugary processed foods with cheese and red meat, but also with unsaturated fats such as fish and nuts. Both groups did the same amount of exercise. A low-carb diet was defined as less than 40g a day, and a low-fat diet as under 30% fat a day, of which saturated fat was less than 7% of the total.

So should dieters stop worrying about how much fat they eat and cut down on refined carbohydrates instead?

The solution

This study was relatively small but it was randomised and carried out carefully, with people reporting what they ate every 24 hours. An impressive 80% of people said that they stuck to their diets for the whole year. But, as usual with these studies, this is but one piece of a dietary jigsaw.

Days after this study was released, a meta analysis that added up the results from 48 randomised diet trials in overweight and obese people (these were branded diets such as the Atkins, Weight Watchers, Zone and Rosemary Conley) found that over six months, people on low-carb diets lost 8.6kg (19lb) more than those not on a diet, while those on low-fat diets lost 7.7kg (17lb) more. After a year, this study found no difference in weight loss. It did not look at reductions in heart disease.

The authors of the study, in the Journal of the American Medical Association, say that people often ask which diet is most effective. The answer – surprise, surprise – is that if you can stick to either type of diet, you’ll lose weight.