After one year, the overall average weight loss was 13.7 kilograms (about 30.2 pounds), with no difference between the two groups. Both groups initially (after the first eight weeks) experienced an improvement in mood. However, most measurements of mood revealed a lasting improvement in only those following the low-fat diet, while those on the high-fat diet returned to their initial levels (i.e., mood returned toward more negative baseline levels).

"This outcome suggests that some aspects of the low-carbohydrate diet may have had detrimental effects on mood that, over the term of one year, negated any positive effects of weight loss," the authors write. Potential explanations include the social difficulty of adhering to a low-carbohydrate plan, which is counter to the typical Western diet full of pasta and bread; the prescribed, structured nature of the diet; or effects of protein and fat intake on brain levels of serotonin, a neurotransmitter related to psychological functioning.

There was no evidence that the nutrient content of either diet was associated with changes in cognitive function, since both groups experienced similar changes in thinking and memory performance over time. "Further studies are required to evaluate the effects of these diets on a wider range of cognitive domains," the authors conclude.

archinte.ama-assn/