Effect of Low/High Carb Diets on Cognitive Function
Over the last number of years there’s been considerable public interest in the use of low carbohydrate, high fat diets, to attain successful weight loss. Many health professionals are concerned that such diets may affect psychological function, whereas high carbohydrate, low fat diets have been suggested to improve these functions. Unfortunately, there have been very few studies conducted on this subject.
However, the American Journal of Clinical Nutrition have published a study comparing a low carbohydrate, high fat (LCHF) diet, with a high carbohydrate, low fat (HCLF) diet, specifically looking at their effect on mood, and cognitive function*.
The study looked at 93 overweight, or obese participants, who were randomly assigned to either a LCHF, or HCLF diet for 8 weeks. The LCHF diet provided 35% energy as protein, 4% of energy as carbohydrates, and 61% as fat. The HCLF diet provided 24% energy as protein, 46% of energy as carbohydrates, and 30% as fat, with women consuming around 1428 kcal/day, and men around 1667 kcal/day.
Study findings:
- Both groups lost weight - the LCHF group losing on average 7.8 kg, and the HCLF group losing on average 6.4 kg.
- Both groups showed improvements in psychological well-being, with no significant difference between the groups.
- There was some evidence for less of an improvement in cognitive functioning* with the LCHF diet, with respect to speed of processing.
Conclusions
“Both dietary patterns significantly reduced body weight, and were associated with improvements in mood. 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.”
To be honest, I’m not particularly ‘blown away’ by the findings of this study concerning the higher weight loss seen in the low carbohydrate, high fat group. Previously, it has been shown that in the initial stages, this type of diet will result in more weight loss, than the more conventional high carbohydrate, low fat diets. However, this evens out over time.
A systematic review of low carbohydrate diets found that the weight loss achieved is associated with the duration of the diet, and restriction of energy intake, but not with restriction of carbohydrates.
A study published in the New England Journal of Medicine found that, “The low-carbohydrate diet produced a greater weight loss (approximately 4%), than did the conventional diet for the first six months, but the differences were not significant at one year. The low-carbohydrate diet was associated with a greater improvement in some risk factors for coronary heart disease.” For similar results check out, Ann Intern Med 2004; 140: 77-85.
Personally, I’d like to see further studies being carried out on this topic. I feel that the study needs to be longer in duration, and also should be larger in size, if we are to fully access the cognitive function of participants in greater detail.
For the original research communication, check out American Journal of Clinical Nutrition, or you may want to read MedScape, for a review of this study.
(*Cognitive function: “An intellectual process resulting in an understanding, perception, or awareness of one’s ideas.”)
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