The new study did not randomly assign participants
to eat different amounts of protein, which would have yielded the
strongest evidence. Instead, it compared the diets of people who
went on to develop diabetes and those who did not get the disease.
But the findings do align with other studies.
"Several previous studies have found that higher intake of total
protein, especially animal protein, are associated with long-term
risk of developing diabetes," said Dr. Frank Hu, from the Harvard
School of Public Health in Boston. Hu, who was not involved in the
new study, researches prevention of diabetes through diet and
"Substantial amounts of animal protein come from red meat and
processed meat, which have been consistently associated with
increased risk of diabetes," he told Reuters Health in an email.
For the new report, researchers examined data from a large previous
study of adults in eight European countries spanning 12 years. The
study collected data on participants' diet, physical activity,
height, weight and waist circumference, then followed them to see
who developed diabetes.
A team of researchers led by Monique van Nielen of Wageningen
University in the Netherlands selected 11,000 people who developed
type 2 diabetes from the data and 15,000 people without diabetes for
Overall, the adults in the study commonly ate about 90 grams of
protein per day. Those who ate more tended to have a higher
weight-to-height ratio and to eat more fiber and cholesterol than
people who ate less protein.
After accounting for other diabetes risk factors, every additional
10 grams of protein people consumed each day was tied to a six
percent higher chance that they would develop diabetes.
Dividing participants into five groups based on how much protein
they ate, the researchers found those who ate the most, or around
111 grams per day, were 17 percent more likely to develop diabetes
than those who ate the least, or around 72 grams per day.
Specifically, those who ate the most animal protein, or 78 grams per
day, were 22 percent more likely to be diagnosed with diabetes than
those who ate the least, around 36 grams per day, according to
results published in Diabetes Care.
That's only a modest increase on an individual level, Hu said.
People who ate the most protein got about 15 percent of their
calories from red meat, processed meat, poultry, fish and dairy,
which appears to be too much, Hu said.
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"More importantly, higher intake of animal protein often comes
along with other undesirable nutrients such as saturated fat,
cholesterol and sodium," he said.
The association between animal protein and diabetes risk appeared to
be strongest among obese women.
Plant protein, on the other hand, was not linked to diabetes.
"In other studies, plant protein sources such as nuts, legumes and
whole grains have been associated with lower risk of diabetes," Hu
said. "Therefore, replacing red meat and processed meat with plant
sources of protein is important for diabetes prevention."
Generally people associate high-fat and high-carbohydrate diets
with diabetes risk, but this study underscores that protein is an
important nutrient to consider as well, Paolo Magni said. Magni,
from the Institute of Endocrinology at the University of Milan in
Italy, was not involved in the new study.
"As a general rule, I would suggest to eat normal portions of red
meat not more than two times per week, poultry and fish three to
four times per week, skimmed milk or yogurt maybe not every day,"
Magni told Reuters Health in an email.
Cheese, preserved meats and cold cuts should be minimized, he said.
"Pay attention to both quantity and food sources of protein," Hu
said. It's probably a good idea for people with a family history of
diabetes to replace at least some red meat with nuts, legumes or
whole grains, he said.
Diabetes Care, online April 10, 2014.
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