Low-carbohydrate diets such as the Atkins diet may be bad for the mood, researchers have reported.
A team from the Commonwealth Scientific and Industrial Research Organisation in Australia followed 106 dieters for a year.
Participants were overweight or obese, with an average age of 50. They were randomly allocated to a low-carbohydrate, high-fat diet or a high-carbohydrate, low-fat diet. Both contained between 1,433 and 1,672 kcal per day.
After a year, both groups lost an average of 13.7 kilograms. Type of diet did not affect brain performance, but there were "greater improvements in psychological mood states for the low fat diet compared with the low carbohydrate diet", say the researchers in Archives of Internal Medicine.
Dr Grant Brinkworth and colleagues write: "Over one year, there was a favourable effect of an energy-restricted low fat diet compared with an isocaloric low carbohydrate diet on mood state and affect in overweight and obese individuals."
The researchers explain that weight loss achieved by dieting is known to improve long-term mood in obese individuals. Low carbohydrate diets are effective, but their impact on mood has not previously been rigorously studied.
"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.
They suggest that there are greater "social difficulties" sticking to a low-carbohydrate plan, with its ban on typical Western foods such as pasta and bread. Or it may be that the diet affects brain levels of the neurotransmitter serotonin, which is involved in regulating mood.
"Further studies are required to evaluate the effects of these diets on a wider range of cognitive domains," the authors conclude.
Brinkworth, G. D. et al. Long-term Effects of a Very Low-Carbohydrate Diet and a Low-Fat Diet on Mood and Cognitive Function. Archives of Internal Medicine, Vol. 169, November 9, 2009, pp. 1873-80.
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