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Am Fam Physician. 2010;81(8):1029-1030

Background: Diet-induced weight loss can improve the psychological state and mood of patients who are obese. Preliminary evidence has suggested that a high-carbohydrate, low-fat, calorie-restricted diet may impact mood and cognition differently than a very-low-carbohydrate diet. Brinkworth and colleagues studied the long-term effects of low-fat and very-low-carbohydrate diets on mood.

The Study: The authors of this randomized study enrolled 106 adults who were overweight or obese (mean body mass index = 33.7 kg per m2) to a very-low-carbohydrate diet (4 percent carbohydrate, 35 percent protein, 61 percent fat with 20 percent as saturated fat) or a conventional low-fat diet (46 percent carbohydrate, 24 percent protein, 30 percent fat with less than 8 percent saturated fat) for one year. Both diets were designed to be moderately energy restricted (1,433 kcal per day for women and 1,672 kcal per day for men). In addition to monitoring the participants' body weight, their mood and cognitive functioning were assessed using three validated scales (the Profile of Mood States, the Beck Depression Inventory, and the Spielberger State-Trait Anxiety Inventory). Exclusion criteria included pregnancy, diabetes, cancer, and a history of liver or cardiovascular disease.

Results: Both groups had similar reductions in weight with an average weight loss of 30.2 lb (13.7 kg) at 12 months, as well as similar baseline mood scores. After eight weeks, both groups had similar improvement in mood scores on all three scales, but those on the low-fat diet maintained their improvement whereas the values of the group on the very-low-carbohydrate diet trended toward baseline levels for the remainder of the study. Diet type did not appear to affect cognitive functioning.

Conclusion: The authors conclude that a conventional low-fat diet improves long-term mood scores. In contrast, a very-low-carbohydrate diet has similar initial improvement that reverts toward baseline levels as time progresses. Both diets have similar effects on cognitive functioning.

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