In regards to weight loss, both low-carb and low-fat diets seem to tip the scale the same after a year; but, to feel as if a load has been lifted from your shoulders, you may want to follow a low-fat diet, according to a new study published in the November 9, 2009 issue of Archives of Internal Medicine. After studying 106 overweight and obese individuals for one year, researchers found that those who followed a low-fat diet versus a low-carbohydrate diet experienced greater improvements on measures of mood, despite a similar net weight loss between the two groups. There was no difference between the two diet plans for effects on working memory and speed of processing measures of cognitive function.

During the year of study, investigators measured body weight, mood, and cognitive function of participants at weeks 8, 24, 40, and 52. Each participant met with a dietitian every two weeks for the first eight weeks and then once a month. During these meetings, dietary recommendations were given regarding meal plans and recipe information related to the diet (low-fat or low-carb) that the participant was to follow.

Mood was determined from the results of 3 questionnaires (Profile of Mood States, Beck Depression Inventory, and Spielberger State Anxiety Inventory). Both groups had similar scores on the questionnaires at baseline and both showed improvements in mood after the first 8 weeks of the study. As the investigation continued over the year, the mood scores of subjects following the low-fat diet continued to progress and stabilize, whereas the scores of those consuming the low-carb diet started to return back toward baseline.

The investigators offer the following explanations for the different effect on mood between the two diets:

• Subjects were randomly assigned to either the low-fat or low-carb diet groups without consideration of individual food preferences. Because the traditional dietary recommendations for the Western society is a high-carbohydrate diet, those delegated to the low-carb group may have found it to be more "isolating" to follow the dietary recommendations which would have negatively affected mood state.
• The low-carb diet could have resulted in negative physiological changes in serotonin and neurotrophic factors. Findings of other studies have established a link between low serotonin levels and the presence of depression and anxiety. The researchers explain that while a high intake of carbohydrates can increase serotonin levels, high intakes of fat and protein can decrease concentrations. Investigators also point to the exponential link between brain-derived neurotrophic levels and mood, noting that high-fat diets decrease brain-derived neurotrophic levels.

The authors of the study conclude that further investigation into the effects of the two diets on a wider range of cognitive function (e.g., attention, executive function, and short- and long-term memory) is needed.

Resource

Arch Intern Med. 2009:169(20):1873-1880