No-Carb Diets May Impair Memory

Eliminating carbohydrates from your diet may help you lose weight, but it could leave you fuzzy headed and forgetful, a new study suggests.

One week after starting a weight loss diet that severely restricted carbohydrates, participants in the Tufts University study performed significantly worse on memory tests than participants who followed a low calorie, high-carbohydrate diet.

The low-carb dieters' memory-test performances improved in the following weeks after they began eating some carbohydrates.

"The connection between the foods we eat and how we think doesn't really enter into most people's minds," study co-author and cognitive psychologist Holly A. Taylor, PhD tells WebMD. "But this study demonstrates that the foods we eat can have an immediate impact on brain function."

Carbs Are Brain Fuel

The body breaks carbohydrates into glucose, which it uses to fuel brain activity. Proteins break down into glycogen, which can also be used for fuel by the brain, but not as efficiently as glucose.

So it stands to reason that eliminating carbohydrates from the diet might reduce the brain's source of energy and affect brain function. But there has been little research examining this hypothesis in people following low-carb weight loss diets.

The study by Taylor and colleagues included 19 women between the ages of 22 to 55 who were closely followed after beginning a low-carb weight loss plan similar to the Atkins diet or the low-calorie diet recommended by the American Dietetic Association that includes plenty of fruits, vegetables, and whole grains.

Before starting the diets, the women underwent testing designed to measure long- and short-term memory and attention. The tests were repeated one, two, and three weeks after the diet began.

Low-carb dieters ate virtually no carbohydrates during their first week on the diet. In testing conducted after week one, they performed worse on memory-based tasks than the women following the ADA diet.

Reaction times for those on the low-carb diet were slower and their visual-spatial memories were not as good as the low-calorie dieters.

They did perform better than the low-calorie dieters in testing that measured attention and the ability to stay on task, however.

And their performance on the memory tests improved after week one, when limited carbohydrates were reintroduced into their diets.

"Although this study only tracked dieting participants for three weeks, the data suggest that diets can affect more than just weight," Taylor notes in a news release. "The brain needs glucose for energy and diets low in carbohydrates can be detrimental to learning, memory, and thinking."

The study is published in the February 2009 issue of the journal Appetite.

More Study Needed

Australian research scientist Grant D. Brinkworth, PhD, tells WebMD that the findings, while intriguing, do not prove that low-carbohydrate weight loss diets affect memory.

In a study published in 2007, Brinkworth and colleagues performed cognitive function testing on dieters after they had been on either a low-carb or high-carb weight-loss diet for eight weeks.

Both groups lost weight and showed improvements in mood.

The low-carbohydrate dieters showed slight impairments in cognitive processing speed, but no difference was recorded between the two groups in working memory.

Brinkworth says if eliminating carbohydrates from the diet does affect memory, the effect may only be temporary.

"What (Taylor and colleagues) recorded may be an acute, transient effect that may just be the body readjusting to an unfamiliar diet," he says. "We really need studies that examine the long-term impact of these diets on cognition."

Calls to a representative from the private equity firm North Castle Partners, which owns controlling interest in Atkins Nutritional Holdings, were not immediately returned.
By Salynn Boyles
Reviewed by Brunilda Nazario
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