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Protein-Rich Diet Boosts
Benefit Of Exercise
Everyone knows that a good weight-loss program combines diet
and exercise, but a new University of Illinois study reports that
exercise is much more effective when it's coupled with a protein-rich
diet.
"There's an additive, interactive effect when a protein-rich diet
is combined with exercise. The two work together to correct body
composition; dieters lose more weight, and they lose fat, not
muscle," said Donald Layman, a U of I professor of food science
and human nutrition.
A higher-carbohydrate, lower-protein diet based on the USDA food
guide pyramid actually reduced the effectiveness of exercise,
Layman said.
Forty-eight adult women participated in Layman's 4-month study,
published in the August 2005 issue of the Journal of Nutrition.
One group ate a protein-rich diet designed to contain specific
levels of leucine, one of the essential amino acids. A second
group consumed a diet based on the food guide pyramid, which contained
higher amounts of carbohydrates.
Both groups consumed the same number of calories, but the first
group substituted high-quality protein foods, such as meats, dairy,
eggs, and nuts, for foods high in carbohydrates, such as breads,
rice, cereal, pasta, and potatoes.
"Both diets work because, when you restrict calories, you lose
weight. But the people on the higher-protein diet lost more weight.
Some people refer to this as the metabolic advantage of a protein-rich
diet," said Layman.
The study included two levels of exercise. "For one group, we
recommended that they add walking to their lives. They usually
walked two to three times a week, less than 100 minutes of added
exercise," the researcher said.
The other group was required to engage in five 30-minute walking
sessions and two 30-minute weightlifting sessions per week. In
both groups of dieters, the required exercise program helped spare
lean muscle tissue and target fat loss. But, in the protein-rich,
high-exercise group, Layman noted a statistically significant
effect. That group lost even more weight, and almost 100 percent
of the weight loss was fat, Layman said. In the high-carbohydrate,
high-exercise group, as much as 25 to 30 percent of the weight
lost was muscle.
While this protein-rich diet works for everyone, it seems to be
even more effective for people who have high triglyceride levels
and carry excess weight in their midsection--a combination of
health problems known as Syndrome X.
"The protein-rich diet dramatically lowered triglycerides and
had a statistically significant effect on trunk fat, both risk
factors associated with heart disease," he said. "Exercise helped
dieters lose an even greater percentage of body fat from the abdominal
area."
The protein-rich diet works so well because it contains a high
level of the amino acid leucine. Leucine, working together with
insulin, helps stimulate protein synthesis in muscle. "The diet
works because the extra protein reduces muscle loss while the
low-carbohydrate component gives you low insulin, allowing you
to burn fat," he said.
"We believe a diet based on the food guide pyramid actually does
not provide enough leucine for adults to maintain healthy muscles.
The average American diet contains 4 or 5 grams of leucine, but
to get the metabolic effects we're seeing, you need 9 or 10 grams,"
he noted.
To achieve that leucine level, the researcher recommended adding
dairy, meat, and eggs, all high-quality proteins, to the diet.
According to Layman, losing weight doesn't have to mean relying
on supplements to fill in nutritional gaps in your diet. "If you
use a high-quality protein approach to your diet, you can actually
improve the overall quality of your diet while losing weight,"
he said.
Reference
Source 127
August
30, 2005
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