Recent study has shown that people on low-calorie, low-fat diet are happier as compared to people on a low-carbohydrate diet. The obesity epidemic has sparked concerns over health benefits of different diets, however, the effects of these diets on bodily function, including mood and cognition have not been investigated in detail.

Research team led by Grant D. Brinkworth, Ph.D., of Commonwealth Scientific and Industrial Research Organisation–Food and Nutritional Sciences, Adelaide, Australia, conducted a randomized clinical trial to study the moods of people on different diets.  

Around 106 overweight and obese participants with an average age of 50 were randomly assigned either of the diets. 55 participants were asked to follow a very–low-carbohydrate, high-fat diet, while 51 were assigned a high-carbohydrate, low-fat diet for one year.

Data regarding body weight, mood and well-being, and cognitive functioning was collected periodically for one-year. Data analysis showed that average weight loss was 13.7 kilograms (about 30.2 pounds) in the two groups.  

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