A low-carbohydrate/high-fat diet and a high-carbohydrate/low-fat diet both improve weight loss, enhance mood, and speed thinking, a study shows, but the low-carb diet may offer less benefit in terms of the rate of cognitive processing.

“In overweight and obese patients, following an energy-restricted dietary plan for weight loss is associated with improvements in mood, regardless of macronutrient composition,” Dr. Grant D. Brinkworth told Reuters Health.

Moreover, while both a high- and low-carbohydrate diets seem to boost the speed of cognitive processing, “the interesting result was that compared to the high-carbohydrate diet, subjects consuming the low-carbohydrate diet had a smaller improvement,” Brinkworth noted.

Brinkworth, of the Commonwealth Scientific and Industrial Research Organisation-Human Nutrition, in Adelaide, Australia and colleagues compared mood and cognitive function in overweight or obese, but otherwise healthy, men and women who were between 24 to 64 years old.

Over 8 weeks, participants followed one of two diets of similar caloric and macronutrient content, the researchers report in the American Journal of Clinical Nutrition.

The low-carbohydrate diet contained 35 percent total protein, 61 percent total fat (20 percent saturated fat) and 4 percent total carbohydrate. The high-carbohydrate diet consisted of 24 percent total protein, 30 percent total fat (less than 8 percent from saturated fat), and 46 percent total carbohydrate.

The researchers found no changes in mood among the 93 participants consuming either the low- or high-carbohydrate diet for the study duration. They did find, however, a small between-group difference, favoring the high-carb dieters, in the speed in which participants performed intelligence and reasoning tests.

The findings suggest, Brinkworth noted, that “very low carbohydrate diets may offer less benefit than a high carbohydrate diet for improving cognitive function.”

The investigators say further research is needed to determine whether similar outcomes occur with similar diets of longer duration.

SOURCE: The American Journal of Clinical Nutrition, September 2007.