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But as for mood? Only the low-fat diets will result in long-term improvement in mood, according to a study in the Nov. 9 issue of Archives of Internal Medicine.
People on both diets consumed roughly the same number of calories.
"Both an energy-reduced, very low-carbohydrate, high-fat diet and a conventional high-carbohydrate, low-fat diet are equally effective for achieving weight loss in overweight and obese individuals," explained study author Grant D. Brinkworth, a research scientist with the food and nutritional sciences division of the Commonwealth Scientific and Industrial Research Organisation in Adelaide, Australia.
"Both dietary patterns also had similar effects on the cognitive domains assessed," which were working memory and speed of processing, Brinkworth added. "However, the conventional high-carbohydrate, low-fat weight-loss diet was shown to have more positive effects on mood compared to the very low-carbohydrate, high-fat diet."
Dr. Ewald Horvath, interim chairman of psychiatry at the University of Miami Miller School of Medicine, said the study was the first "to show both long-term weight loss and improved mood."
"This study looked at one factor, and prior studies haven't focused on psychological factors," Horvath said. "This is a great study focusing on something very important."
But few studies have looked at long-term mood changes among people who lose weight.
Health organizations, such as the American Heart Association, tend to advocate higher-carb, low-fat diets. But many overweight and obese people are propelled toward the high-fat diets such as Atkins, "Livin' La Vida" and "Good Calories, Bad Calories," perhaps because of quick initial weight loss, Horvath said.
For the new study, 106 overweight and obese adults, who averaged 50 years old, were randomly assigned to one of two diets -- a low-calorie, low-carb, high-fat plan or a high-carb, low-fat diet -- for one year. Both diets restricted calories to about 1,433 to 1,672 a day.
A year later, average weight loss was about the same in each group: 30.2 pounds.
After the first eight weeks, participants in both groups showed mood improvements, but that lasted only in the low-fat group. After a year, the mood of those in the high-fat group returned to what it had been before they started dieting, the study found.
"The exact mechanism for the observed effects on mood still remains largely unknown," Brinkworth said. "However, if the mechanism for the return of mood toward more negative baseline levels following weight loss with a very low-carbohydrate diet is related to this diet being so far removed from normal dietary habits, then a very low-carbohydrate diet may be best recommended for individuals who habitually consume low amounts of carbohydrate foods in their diet."
More carbs can increase serotonin concentrations in the brain, whereas added fat and protein can reduce concentrations. Serotonin is a neurotransmitter involved in mood.
"Altered mood has been shown to influence interpersonal behavior and, therefore, the consumption of a very low-carbohydrate diet may have psychosocial consequences for interpersonal behavior and relationships," Brinkworth said. "I am not entirely clear as to the effects of mood on long-term weight loss; however a recent review article ... suggested that one of the factors that may pose risk for poor long-term weight maintenance may be 'eating in response to negative emotions and stress.'"
"Therefore, since negative mood may promote overeating, this suggests that consumption of a very low-carbohydrate diet over an even longer period beyond one year may have implications for maintaining dietary habits and weight loss maintenance," he added. "Further, longer-term studies would be required to confirm this."
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