Low-Carb Diets May Impact Brain Function

With obesity at epidemic proportions, people continue to look for ways to lose weight where minimal effort is required. Currently, there are over 135 diets being promoted across America, where an estimated $50 billion a year is spent on dieting. One of the most popular diets has been the Atkins Diet that became popular in the 1970s, fell into decline for a time only to return to prominence. The Atkins system virtually eliminates carbohydrates like pasta, bread, potatoes and even some fruits and vegetables, yet allows many of the foods that are considered fatty and unfit for dieting. And while the diet manages to have a high success rate at losing weight, there are a lot of possible negative consequences of such a lifestyle.

One of the side effects of the Atkins diet, as well as any no- to low-carbohydrate diet, is your body being in ketosis, the process of your body switching from using carbohydrates to using fats for energy, which can result in bad breath, weakness, nausea, dizziness, and insomnia. Another side effect is constipation, caused in part from the lack of high-fiber foods. Other side effects are more on the long-term spectrum, including the risk of heart disease, a chance of osteoporosis, colon cancer, kidney problems and premature aging. Now, researchers say there is yet another side effect of carb-restrictive diets—memory loss.

Researchers believe this may be due to the way our brains use glucose, which comes from breaking down carbohydrates. Glucose is needed in order to power our brain cells, and since they have no way of storing it, these cells rely on a continuous supply via the bloodstream. When carbohydrate intake is reduced, so is the body’s ability to keep the brain supplied with glucose, thus resulting in impaired cognition.

Professor Holly Taylor from Tufts University in Medford, Massachusetts led a recent study that monitored nineteen women between the ages of 22 and 55; nine of whom began an Atkins-style low-carb diet while ten chose a low-calorie diet as recommended by the American Dietetic Association that included plenty of fruits, vegetables, and whole grains. The participants attended five assessment sessions designed to measure short- and long-term memory and attention; one just before starting their chosen diets, 2 and 3 during the first week of dieting and 4 and 5 during weeks 2 and 3 of the study. They were also asked questions about their mood and how hungry they felt.

Tests conducted after week one, when the low-carb dieters ate virtually no carbohydrates, showed the low-carb dieters performed worse on memory-based tasks than the group following the low-cal diet. Their reaction times were also slower and their visual-spatial memories were not as good as the low-cal group. However, they did perform better than the low-cal group in tests that measured attention and the ability to stay on task and their mental function appeared to return to normal after week one, when carbohydrates were reintroduced into their diets, which builds on previous study results showing short-term improvements in attention for people on high protein or high fat diets. Hunger levels remained consistent between the two groups, and the only difference in mood was seen in the low-calorie dieters who reported feeling more confused during the middle period of the study. “This study demonstrates that the food you eat can have an immediate impact on cognitive behavior. The popular low-carb, no-carb diets have the strongest potential for negative impact on thinking and cognition,” said Professor Taylor. “The brain needs glucose for energy and diets low in carbohydrates can be detrimental to learning, memory and thinking.”

However, Australian research scientist Grant D. Brinkworth, Ph.D., says these effects may be temporary, “just the body readjusting to an unfamiliar diet.” In a study published in 2007, Brinkworth and colleagues also conducted cognitive testing on dieters after they had been on either a low-carb or high-carb diet for eight weeks. In their test, the low-carb dieters showed slight impairments in cognitive processing speed, but no difference in working memory compared to the high-carb group. He calls for studies to examine the long-term impact these diets have on cognition.

Taylor’s study is published in the February 2009 issue of the journal Appetite, but is already available for viewing online.