“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 difficulties sticking to a low carbohydrate plan, with its ban on typical Western foods such as pasta and bread. In this study, participants did not choose their diet, but were randomly assigned to one or the other, so their diet may not have suited their food preferences and eating habits.
“The low carbohydrate diet being so far removed from normal dietary habits may have created a significant challenge for participants,” say the researchers, “leading to the possibility of food preoccupation, social eating impairment, and dysphoria [low mood].”
Another possible explanation for the results is that the low carbohydrate 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.
Previous studies have not found any differences in mood between dieters following low fat and low carbohydrate diets, although the studies have tended to be small and short-term. However, one study, over a longer duration of 24 weeks, found better mood among dieters on a low carbohydrate ketogenic diet, whose energy production was altered by a very low intake of carbohydrates leading to ketogenesis.
In that study, researchers from Duke University in Durham, North Carolina did not control for energy intake. This led to significantly greater weight loss with the low carbohydrate diet, which may have accounted for the improved mood. What’s more, individuals on the low carbohydrate diet took nutritional supplements, while those in the low fat group did not.
Writing in the journal Obesity, the team state, “Regardless of diet, participants experienced significant improvement in a broad range of symptoms. Symptoms of negative mood and hunger improved to a greater degree in patients following a low carbohydrate ketogenic diet compared with those following a low fat diet.”
They add that hunger was significantly lessened on the low carbohydrate diet, for up to three months. Such appetite suppression has also been shown in earlier studies of low carbohydrate/high protein diets. Because this type of diet restricts only one class of food (instead of several, as in a typical low calorie approach), the researchers suggest that dieters experience fewer food cravings and greater satisfaction after meals.
The findings took into account each dieter’s weight loss, so the improved mood is “likely attributable to the diet,” say the authors. They conclude that, “Further trials seeking to understand the mechanisms underlying these effects are warranted.”
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.
McClernon, F. J. et al. The effects of a low-carbohydrate ketogenic diet and a low-fat diet on mood, hunger, and other self-reported symptoms. Obesity, Vol. 15, January 2007, pp. 182-87.