Since the analysis includes studies with different designs, there is
a chance that something other than protein intake might explain the
results, said co-author Dr. Xinfeng Liu of Nanjing University School
of Medicine in China.
“Dietary protein intake tends to be associated with other nutrients
that may prevent stroke, such as potassium, magnesium and dietary
fiber,” so the findings should be interpreted with caution, Liu told
Reuters Health in an email.
Still, the relationship between protein and stroke persisted when
the researchers only looked at studies that took those factors into
account, he noted.
Close to 800,000 people in the United States have a stroke each
year, according to the Centers for Disease Control and Prevention.
The new review includes seven studies, each of which followed a
group of adults for at least 10 years. Participants either
periodically filled out diet questionnaires or were asked to recall
everything they had eaten over the past 24 hours in order to gauge
their protein intake, and researchers recorded which of them had a
stroke during the follow-up period.
The studies included a combined total of about 255,000 people.
Four of the studies took place in the U.S., two in Japan and one in
Sweden. Most considered any type of stroke, but two focused on fatal
Six of the studies found that as protein intake increased, stroke
risk decreased. But in three of those studies the relationship was
weak enough that it could have been due to chance, according to
findings published in Neurology.
All together, the review authors found that people who ate the most
protein were about 20 percent less likely to have a stroke than
those who ate the least. An extra 20 grams of protein per day was
linked to a 26 percent lower stroke risk.
Most of the studies accounted for age, sex and diabetes history as
factors in stroke risk.
Eating protein may help lower blood pressure, which in turn lowers
stroke risk, the authors write. Still, there could be other
explanations for the findings.
“The results of this meta analysis should be interpreted carefully,”
said Dr. Arturo Tamayo, who studies stroke prevention at the
University of Manitoba in Winnipeg. He co-wrote an editorial
accompanying the analysis.
Diet can influence stroke risk, but in many ways, not just through
protein intake, he told Reuters Health by email. Genetic
predisposition for increased cholesterol, age and other medical
conditions like high blood pressure or heart disease can also
influence risk, he said.
“The results of this study show us a ‘trend’ of a positive factor in
diet that can contribute to decrease the risk of stroke,” he said.
ANIMAL VERSUS PLANT PROTEIN
Animal protein was linked to a greater reduction in stroke risk than
other sources of protein in the new report. But another recent
analysis published in JAMA Internal Medicine found that vegetarian
diets are associated with lower blood pressure than diets that
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In the current analysis, there wasn’t a big range in plant protein
intake - those who ate the most ate only 16 more grams per day than
those who ate the least - compared to animal protein, where the
daily range was 35 grams, Liu said.
Since there wasn’t a big range in plant protein consumption, it was
harder to find an association with stroke, he said.
Relatively few people in the included studies got their protein from
grains, which could have factored in as well, Tamayo said.
“Among different protein sources, fish consumption has been
associated with decreased risk of stroke, whereas red meat
consumption has been associated with increased stroke risk,” Liu
The saturated fat and cholesterol in red meat may increase stroke
risk, so red meat isn’t the best source of protein for people
worried about stroke, he said.
“Thus, stroke risk may be reduced by replacing red meat with other
protein sources such as fish,” Liu said. “Fish contains omega-3
fatty acids and some other nutritional elements including protein
that may protect against stroke.”
“As stroke neurologists we aim to change as much as possible all
those factors that can potentially be modified, like cholesterol and
hypertension, among others and lifestyle factors such as lack of
exercise, cigarette smoking, alcohol consumption and diet,” Tamayo
It is important that people understand how much diet can influence
the advent of multiple diseases, he said.
“Global strategies to prevent stroke should start early in life with
an adequate diet education for all people regardless of their risk
of stroke,” he said.
The human diet and stroke prevention are both incredibly complex, he
said, but current evidence tilts toward a largely vegetarian Cretan
Mediterranean diet high in whole grains, olive oil, fish and fruit,
and low in red meat as beneficial for stroke reduction.
Neurology, online June 11, 2014.
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