The benefit of healthy eating and fitness training for people looking to lose weight is well known, but research suggests those who cut carbohydrates out of their diet are likely to be grumpy.

On the other hand, a low-fat diet can actually make people happier, scientists have found.

Research teams compared a low-carbohydrate diet that was high in fat and protein with a low-fat diet rich in carbs, tracking 106 overweight people on the two diets over the course of a year.

The study, published by the American Medical Association, found that while the two diets produced similar weight loss, those eating more carbohydrates were much happier.

"No one got grumpier than when they started out, but those on the low fat diet got happier and those on the low carb diet didn't get that benefit - they in some cases reverted back to where they were at base line," said researcher Professor Jon Buckley.