Low-carb diets lead to grumpy moods

Diets low in carbohydrates that limit intake of foods like bread, pasta and potatoes produce good weight loss, but make people grumpy, a study has found.

The study compared a low-carbohydrate diet that was high in fat and protein with a low-fat diet rich in carbs. It found that while they produced similar weight loss, those eating more carbohydrates were much happier.

Scientists from the CSIRO, South Australia University and Flinders University tracked 106 overweight people on the two diets over the course of a year. Participants were weighed and filled out questionnaires about their emotional state at weeks eight, 24, 40, and 52.

The results showed rapid improvement in the moods of people in both groups during the first eight weeks, but then a regression in these gains in the group eating a diet low in carbohydrates for the rest of the year. In contrast, those on the low-fat diet that was rich in carbs experienced considerably less depression, tension, anxiety and feelings of hostility.

The study, which appears in the Archives of Internal Medicine, published by the American Medical Association, also assessed changes in the cognitive function of participants, but found no significant trends between the two groups. People in both groups lost an average of 13.7 kilograms each.

On the low-carb plan, diets consisted of 4 per cent carbohydrate, 35 per cent protein and 61 per cent fat, while the high-carb diet had 46 per cent carbohydrate, 24 per cent protein and 30 per cent fat. Each group was allowed the same number of calories daily, about 1400 for women and about 1700 for men.

The deputy director of the Nutritional Physiology Research Centre at the University of South Australia and one of the researchers, Jonathan Buckley, said the mood difference could reflect how difficult it is to comply with a low-carb diet in Australia, where the typical diet is about 50 per cent carbohydrate.

''If you're eating a low-carb diet and you're out with friends at a restaurant, it might be more difficult to stick with that diet because restaurants don't offer many other options,'' he said.

Associate Professor Buckley said previous research had also shown that a diet high in saturated fat could affect blood vessel function, including in the brain.

''This has the potential to alter people's moods ... but we're not certain about that at this stage. More research is required to look at that,'' he said.