Lower Carbs Leads to Diminished Brain Function

A new study out of Tufts University has uncovered a major drawback to “low-carb diets,” which have garnered a large contingency over the past decade. The study revealed that low-carb diets induce decreased cognitive ability, especially memory.

Low-carbohydrate diets have an extremely long history (our nomadic hunter ancestors from many thousands of years ago are thought to have consumed little, or no, carbohydrates), but have only become popular in western society, as a method of weight loss and control, in the past ten years. A low-carb diet is typically defined by carbohydrates accounting for less than 20% of one’s daily caloric intake. This translates to approximately 60 grams, or less, of carbohydrates per day.

The “low carb craze,” which began in the late 1990’s and has extensions to the present day (though popularity has decreased), was most identifiably brought on by the Atkins diet. Low-carb diets are founded most generally on the following major principles: Carbohydrate consumption leads to insulin production, which allows excess carbohydrates to be stored as energy in the body, through fat. If carbohydrate consumption is low, insulin production is discouraged, and it’s believed by many that excess energy and body fats are then eliminated in a process called ketosis.

The above principles are engineered almost specifically as a way to lose weight, with little consideration for general health. While obesity has been linked to many diseases, including diabetes and heart disease, proper nutrition is also essential for the prevention of these conditions as well. More direct evidence has also suggested that low-carb diets, in extreme forms (where necessary nutrients become neglected due to strict adherence to protein-based diets), in fact promote heart disease, and are dangerous for diabetics (interestingly, the progenitor of the Atkins diet, Dr. Robert Atkins, apparently had a history of heart disease and hypertension). All these considerations have made low-carb diets extremely controversial, and highly researched, though until now there was little direct connection between cognitive function and low-carb diets.

The current study began with the knowledge that energy for the brain comes in the form of glucose, which is often supplied through the breakdown of carbohydrates. Therefore, it seemed possible from the outset, that low-carb diets would give the brain less “fuel,” and therefore diminish its function.

This speculation was shown to be correct through the study of 19 women between 22-55 years of age. Nine women observed a low-carb diet, while 10 women followed a balanced, low-calorie, diet. Five series of cognitive tests were administered, in which memory (short-term, long-term and “spatial”) and attention were of primary focus. The first test came before the women went on their respective diets, two tests occurred during their dieting, and two after carbohydrates were re-introduced to the low-carb group. The study took place over a three week period.

Study author Dr. Holly A. Taylor explains that “although the study had a modest sample size, the results showed a clear difference in cognitive performance as a function of diet. The data suggest that after a week of severe carbohydrate restriction, memory performance, particularly on difficult tasks, is impaired.” Specifically, visual, short-term and long-term memory function, decreased in the low-carb dieters, while no such effect was seen in the low-calorie dieters. Attention, however, was seen to improve in low-carb dieters, supporting past research that has suggested protein consumption makes individuals more alert. It was also noted that normal brain function returned to the low-carb women once they started eating carbohydrates again.

As long as weight comes off, it’s expected that low-carb diets will continue to maintain a large following. But for those more concerned with the health aspects of weight loss, as opposed to the more vain aspects of the endeavour, there is mounting evidence that this type of diet can do more harm than good. This current study has confirmed the speculation that low-carbs translate to less fuel for the brain. “The brain needs glucose for energy and diets low in carbohydrates can be detrimental to learning, memory, and thinking. The popular low-carb, no-carb diets have the strongest potential for negative impact on thinking and cognition,” concludes Dr. Taylor. Just another knock against this poorly supported form of dieting.

Source: Defeat Diabetes Foundation: Taylor, Holly. Miller, Suzanne. Tufts University news release. December 2008.