Tufts: Low-carb diets can affect dieters' cognition skills

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Public release date: 11-Dec-2008

http://www.eurekalert.org/pub_releases/2008-12/tu-ldc121108.php

Contact: Suzanne

suzanne_c.miller@...

Tufts University

Low-carb diets can affect dieters' cognition skills

Tufts study compared women's cognition on low-carb and reduced-calorie diets

MEDFORD/SOMERVILLE, Mass. -- A new study from the psychology department

at Tufts University shows that when dieters eliminate carbohydrates from

their meals, they performed more poorly on memory-based tasks than when

they reduce calories, but maintain carbohydrates. When carbohydrates

were reintroduced, cognition skills returned to normal.

" This study demonstrates that the food you eat can have an immediate

impact on cognitive behavior, " explains Holly A. , professor of

psychology at Tufts and corresponding author of the study. " The popular

low-carb, no-carb diets have the strongest potential for negative impact

on thinking and cognition. "

collaborated with Professor Robin Kanarek, former undergraduate

Kara Watts and research associate D'Anci. The study,

" Low-carbohydrate weight-loss diets. Effects on cognition and mood, "

appears in the February 2009 edition of the journal " Appetite. "

While the brain uses glucose as its primary fuel, it has no way of

storing it. Rather, the body breaks down carbohydrates into glucose,

which is carried to the brain through the blood stream and used

immediately by nerve cells for energy. Reduced carbohydrate intake

should thus reduce the brain's source of energy. Therefore, researchers

hypothesized that diets low in carbohydrates would affect cognitive skills.

Study participants included 19 women ages 22 to 55 who were allowed to

select the diet plan they preferred -- either a low-carbohydrate diet or

a low-calorie, macronutrient balanced diet recommended by the American

Dietetic Association. Nine women chose a low-carbohydrate diet and 10

selected the low-calorie diet.

" Although the study had a modest sample size, the results showed a clear

difference in cognitive performance as a function of diet, " says .

The 19 dieters completed five testing sessions that assessed cognitive

skills, including attention, long-term and short-term memory, and visual

attention, and spatial memory. The first session was held before

participants began their diets, the next two sessions occurred during

the first week of the diet, which corresponded to the week when low-carb

dieters eliminated carbohydrates. The final two sessions occurred in

week two and week three of the diets, after carbohydrates had been

reintroduced for those on the low-carb diet.

" The data suggest that after a week of severe carbohydrate restriction,

memory performance, particularly on difficult tasks, is impaired, "

explains.

Low-carb dieters showed a gradual decrease on the memory-related tasks

compared with the low-calorie dieters. Reaction time for those on the

low-carb diet was slower and their visuospatial memory was not as good

as those on the low-calorie diet. However, low-carb dieters actually

responded better than low-calorie dieters during the attention vigilance

task. Researchers note that past studies have shown that diets high in

protein or fat can improve a person's attention in the short-term, which

is consistent with the results in this study.

Participants were also asked about their hunger levels and mood during

each session. The hunger-rating did not vary between participants on a

low-carb diet and those on a low-calorie diet. The only mood difference

between dieters was confusion, which was higher for low-calorie dieters

during the middle of the study.

" Although this study only tracked dieting participants for three weeks,

the data suggest that diets can affect more than just weight, " says

. " The brain needs glucose for energy and diets low in

carbohydrates can be detrimental to learning, memory and thinking. "

--

ne Holden, MS, RD

" Ask the Parkinson Dietitian " http://www.parkinson.org/

" Eat well, stay well with Parkinson's disease "

" Parkinson's disease: Guidelines for Medical Nutrition Therapy "

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