DIET/HEALTH/NUTRITION
Study shows protein-rich diet and exercise
improve body composition
by Caroline Margolis
Manager, Nutrition Partnerships – NCBA
Summary
Checkoff-funded research conducted by Donald Layman,
Ph.D., and his team at the University of Illinois UrbanaChampaign, found exercise is much more effective when
it’s coupled with a protein-rich diet. Published in the August
2005 Journal of Nutrition (“Dietary Protein and Exercise
Have Additive Effects on Body Composition During Weight
Loss in Adult Women”), this study adds to the growing body
of evidence supporting the beneficial role of lean beef in
weight management.
Background
For decades, nutrition experts and the public have
debated the ideal combination of protein, carbohydrates and
fat in the diet. New research, funded in part with checkoff
dollars, explains for the first time how exercise is more
effective in conjunction with a high-protein diet, resulting
in a more effective weight-loss routine. The research,
conducted at the University of Illinois and published in the
August 2005 edition of Journal of Nutrition, demonstrates
that high protein diets provide a metabolic advantage that
when combined with exercise, resulted in dieters losing fat
rather than muscle.
Two different diets and two different
exercise levels
Layman’s team tested two different diets by following
the 48 women who participated in the randomized, fourmonth weight-loss trial. 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. All of the women consumed the same
number of calories, but the protein group substituted highquality protein foods, such as meats, dairy, eggs and nuts,
for foods high in carbohydrates, such as breads, rice, cereal,
pasta and potatoes.
Both diets were designed to provide 1,700 calories,
57 gram of fat and 17 grams of fiber per day. Both diets
also fell within the Acceptable Macronutrient Distribution
Range established by the Institute of Medicine; however,
the Protein Group followed a low carbohydrate-to-protein
ratio (<1.5, with approximately 30% of energy coming
20 ISSUES UPDATE
from protein) and the Carbohydrate Group followed a high
carbohydrate-to-protein ratio (>3.5, with approximately 15%
of energy coming from protein).
The study design called for two different levels of
exercise within each group. The first level of exercise
involved walking between two and three times a week for
less than 100 minutes of added exercise. Level-two exercise
required the women to engage in five 30-minute walking
sessions and two 30-minute weightlifting sessions per week.
Protein-rich diet helps protect muscle,
burn fat
Both groups of dieters found the required exercise
helped spare lean muscle tissue and target fat loss, but in the
protein-rich, high-exercise group, the effect was statistically
significant. This group not only lost more weight but in
addition, almost 100 percent of the weight loss was fat. In
the high-carbohydrate, high-exercise group, as much as 25
percent to 30 percent of the weight lost was muscle.
Muscle helps the body burn more calories so it is
critical to maintain muscle mass during weight loss. The
protein-rich diet also dramatically lowered triglycerides
and had a statistically significant effect on abdominal fat,
both risk factors associated with heart disease. The diet also
maintained higher HDL (good) cholesterol levels.
Leucine key to success of protein-rich diet
The study results suggest protein-rich diets work well
because they contain a higher level of the amino acid
leucine. Leucine, working together with insulin, helps
stimulate protein synthesis in muscle. Therefore, the extra
protein protects against muscle loss while less carbohydrates
helps maintain low insulin, allowing dieters to burn fat.
Leucine is an essential amino acid – or protein building
block – that cannot be made by the body. Therefore, it is
necessary to consume it in high-quality protein sources such as
beef and dairy products. High-quality proteins provide the right
amounts of all the essential amino acids, or “building blocks,”
the body needs in order to grow and function properly. Lean
beef is among the best sources of high-quality protein.
Researchers believe a diet based on the food guide
pyramid does not provide enough leucine for adults to
maintain healthy muscles. The average American diet
contains 4 or 5 grams of leucine per day, but to achieve
SEPTEMBER-OCTOBER 2005
DIET/HEALTH/NUTRITION
the metabolic effects seen in this study, 9 or 10 grams is
recommended. Lean beef contains on average about 2 grams
of leucine per 3-ounce serving.
Because Journal of Nutrition is peer-reviewed, a panel of
third-party experts reviewed this study to ensure its validity.
Key Points
• An August 2005 Journal of Nutrition study, funded
in-part with checkoff dollars, found that a proteinrich diet combined with exercise helps dieters
improve body composition, reduce triglyceride
levels and maintain better cholesterol levels.
• Compared to the carbohydrate group, women in
the protein group experienced greater total weight
loss, more fat loss and less loss of lean muscle
mass after the four-month trial.
• The study also found that the essential amino acid
leucine stimulates protein synthesis in muscle
and reduces muscle loss in dieters. Lean beef is a
high-quality protein, and therefore a naturally-rich
source of leucine.
SEPTEMBER-OCTOBER 2005
ISSUES UPDATE 21