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Low-Carb Diets can
affect Dieters' Cognition skills
Newswise — 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.
Taylor, 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."
Taylor collaborated with Professor Robin
Kanarek, former undergraduate Kara Watts and
research associate Kristen D'Anci.
The study, "Low-carbohydrate weight-loss
diets. Effects on cognition and mood,"
appears in the February 2009 edition of the
While the brain uses glucose as its primary
fuel, it has no way of storing it.
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
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 Taylor.
The 19 dieters completed five testing
sessions that assessed cognitive skills,
including attention, long-term and
short-term memory, and visual attention, and
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
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," Taylor explains.
Low-carb dieters showed a gradual decrease
on the memory-related tasks compared with
the low-calorie dieters.
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.
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
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 Taylor.
"The brain needs glucose for energy and
diets low in carbohydrates can be
detrimental to learning, memory and
Tufts University, located on three
Massachusetts campuses in Boston,
Medford/Somerville, and Grafton, and in
Talloires, France, is recognized among the
premier research universities in the United
Tufts enjoys a global reputation for
academic excellence and for the preparation
of students as leaders in a wide range of
A growing number of innovative teaching and
research initiatives span all Tufts
campuses, and collaboration among the
faculty and students in the undergraduate,
graduate and professional programs across
the university's schools is widely