Low-Carb Diets Affect Your Brain

Low-carb diets seem like an easy way to lose weight: just cut out all carbs. No worrying about portion size, balanced meals or avoiding low-quality, fatty foods - it's "dieting without hunger!" Still, you've probably heard that low-carb diets may not be good for your liver.

They don't appear to be good for your brain, either. Your brain runs primarily on glucose, which comes mostly from the breakdown of carbohydrates in your stomach and intestines. From there the glucose is circulated through the bloodstream to the brain and other organs.

The liver has its own enzymes to help it break down amino acids (proteins) and fats into glucose, but the brain does not. Its only source of glucose is the glucose that is circulated through the bloodstream. The muscles and liver are able to store glucose in the form of glycogen, and it can be converted back to glucose when it is needed, but that is only a 1-2 day supply. Daily intake of carbohydrates is essential for the brain to have a steady supply of glucose.

In times of low blood glucose, the brain has been shown to not perform as well as usual at certain cognitive tasks. In short, low blood sugar affects how well your brain thinks.

Researchers at Tufts University, in collaboration with researchers at the US Department of Agriculture, investigated just how much a low-carbohydrate diet might affect brain function (Appetite 2009;52(1):96-103).

Nineteen otherwise healthy but overweight women between the ages of 22 and 25 were recruited to participate in the study which lasted three weeks. The women were able to choose which diet they wanted to follow for those three weeks: either a low-carbohydrate diet similar to the Atkins™ Diet or a standard reduced-calorie diet modelled on the American Dietetic Association recommended diet. Nine women chose to follow the low-carbohydrate diet, while 10 chose the ADA diet.

The dieters attended five cognitive testing sessions: one before they began their diets, two during the first week of their diets, and one each week thereafter. The testing sessions included an assessment of their mood, a measurement of their feelings of hunger and thirst, and then a set of computerized tests to measure their brain's function at certain measurable tasks.

The researchers found that over the three weeks both groups lost less than 2 kilograms (about 4 and a half pounds). In the first week of the diets, when the low-carbohydrate dieters were eating the least amount of carbohydrates (in accordance with Atkins ™ Diet guidelines), the low-carb dieters showed impairment in their short-term and their spatial memory (remembering where items belong on a map) was affected negatively.

What this means for you

The memory changes seen in this study are not particularly serious and were reversed when the women began to add carbohydrates back into their diet. Interestingly, the hunger tests showed similar results regardless of which diet the women were on: apparently a low-carbohydrate diet did not mean "dieting without hunger"! I still can't imagine why anyone would want to follow a diet that removed entire food groups, even for a short time. Better to choose quality foods containing quality calories and enjoy your food!

First posted: January 14, 2009