Low-Carb/High-Fat or High-Carb/Low-Fat Diet Improves Weight Loss, Mood

September 14, 2007 — A low-carbohydrate, high-fat (LCHF) diet and a high-carbohydrate, low-fat (HCLF) diet both improve weight loss and mood, but speed of cognitive processing improves less with the LCHF than the HCLF diet, according to the results of a study published in the September issue of the American Journal of Clinical Nutrition.
"Low-carbohydrate diets are often used to promote weight loss, but their effects on psychological function are largely unknown," write Angela K. Halyburton, from the Commonwealth Scientific and Industrial Research Organisation–Human Nutrition in Adelaide, Australia, and colleagues. "Considering the lack of well-controlled intervention studies, the purpose of the present study was to compare the effects on mood and cognitive function of a moderately energy-restricted LCHF diet with those of an isocaloric, conventional HCLF diet in overweight and obese persons."
In this study, 93 overweight or obese participants were randomized to receive an energy-restricted (about 6000 - 7000 kJ, 30% deficit), planned isocaloric LCHF diet or an HCLF diet for 8 weeks. Mean age was 50.2 ± 0.8 years, and mean body mass index was 33.6 ± 0.4 kg/m2. At baseline and every 2 weeks, participants were weighed and underwent measurement of psychological well-being on the Profile of Mood States, Beck Depression Inventory, and Spielberger State Anxiety Inventory instruments. Cognitive functioning, including working memory and speed of cognitive processing, were evaluated at baseline and at week 8.
Compared with the HCLF diet, the LCHF diet was associated with significantly greater weight loss (7.8 ± 0.4 vs 6.4 ± 0.4 kg; P = .04). Improvements in psychological well-being were similar in both groups, with the greatest effect observed during the first 2 weeks. Although working memory was similar in both groups (P = .68), there was a significant time/diet interaction for speed of processing (P = .04), with less improvement on this measure in the LCHF than in the HCLF diet group.
"Both dietary patterns significantly reduced body weight and were associated with improvements in mood," the authors write. "There was some evidence for a smaller improvement in cognitive functioning with the LCHF diet with respect to speed of processing, but further studies are required to determine the replicability of this finding."
Study limitations include difficulty separating practice effects from treatment effects; inability to determine the effects of concurrent exercise training; generalizability limited to healthy, overweight, and obese young to middle-aged adults with normal mood state and no cognitive impairment who begin structured diets; and limited measures of cognitive performance.
"Short-term consumption of a moderately energy-reduced LCHF diet has an effect on the psychological well-being of overweight and obese persons similar to that of consumption of an isocaloric conventional HCLF diet," the authors conclude. "However, there was evidence of a somewhat smaller improvement in speed of processing with an LCHF diet. Further studies are required to determine the replicability of this finding and to determine whether similar outcomes are evident over the long term."
The National Heart Foundation of Australia and the National Health and Medical Research Council of Australia supported this study. The authors have disclosed no relevant financial relationships.
Am J Clin Nutr. 2007;86:580-587.