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Item #13
High-Protein
Diet Enhances Weight Loss
Changes
in the ratio of protein to carbohydrate toward a higher protein diet
can be effective in the control of body weight with parallel
improvements in blood lipids.
A
relatively high-protein diet improves body composition, enhances
weight loss, and improves glucose and insulin homeostasis, according
to two reports from the same study group which appear in the February
issue of the Journal of Nutrition.
"Amino
acids interact with glucose metabolism both as carbon substrates and
by recycling glucose carbon via alanine and glutamine; however, the
effect of protein intake on glucose homeostasis during weight loss
remains unknown," write Donald K. Layman and colleagues from the
University of Illinois at Urbana-Champaign.
In
this study, 24 adult women who were more than 15% above ideal body
weight were assigned to either a predominantly protein diet or a
predominantly carbohydrate diet. The protein diet included 1.6
g/kg/day protein, with less than 40% of energy coming from
carbohydrate, while the carbohydrate diet included 0.8 g/kg/day
protein, with more than 55% of energy coming from carbohydrate. Both
diets were equal in calories (7100 kJ/day) and in fat (50 g/day).
After
10 weeks, weight loss was 7.53 ± 1.44 kg in the protein group and
6.96 ± 1.36 kg in the carbohydrate group. Subjects in the
carbohydrate group had lower fasting (4.34 ± 0.10 vs. 4.89 ± 0.11
mmol/L) and postprandial blood glucose (3.77 ± 0.14 vs. 4.33 ± 0.15
mmol/L) and an elevated insulin response to meals (207 ± 21 vs. 75 ±
18 pmol/L).
"This
study demonstrates that consumption of a diet with increased protein
and a reduced carbohydrate/protein ratio stabilizes blood glucose
during nonabsorptive periods and reduces the postprandial insulin
response," the authors write.
According
to a second report from the same study group, "claims about the
merits or risks of carbohydrate vs. protein for weight loss diets are
extensive, yet the ideal ratio of dietary carbohydrate to protein for
adult health and weight management remains unknown."
In
this study, 24 women were assigned to either a predominantly
carbohydrate diet containing 68 g/day protein with a
carbohydrate/protein ratio of 3.5, or to a predominantly protein diet
containing 125 g/day protein with a ratio of 1.4. Each diet provided
7100 kJ/day and approximately 50 g/day of fat. Age range was 45 to 56
years and body mass indices were greater than 26 kg/m2.
After
10 weeks, weight loss was 6.96 ± 1.36 kg in the carbohydrate group
and 7.53 ± 1.44 kg in the protein group. Compared with the
carbohydrate group, weight loss in the protein group had an increased
ratio of fat to muscle loss (6.3 ± 1.2 g/g vs. 3.8 ± 0.9 g/g). Serum
cholesterol reduction was approximately 10% in both groups, but only
the protein group had significant reductions in triacylglycerols (TAG;
21%) and in the ratio of TAG to high-density lipoprotein cholesterol
(23%).
"This
study demonstrates that increasing the proportion of protein to
carbohydrate in the diet of adult women has positive effects on body
composition, blood lipids, glucose homeostasis and satiety during
weight loss," the authors write. "Although it is unlikely
that any one diet will be ideal for all individuals, these results
indicate that changes in the ratio of protein to carbohydrate toward a
higher protein diet can be effective in the control of body weight
with parallel improvements in blood lipids."
The
National Cattlemen's Beef Association and Kraft Foods helped support
this study.
J
Nutr. 2003;133:405-410, 411-417
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FACT:
Improved
control of cholesterol and lipids (for example, HDL, LDL, and
triglycerides) can reduce cardiovascular complications by 20% to 50%.
CDC
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