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.
Source: Diabetes In Control Dot Com: Journal of Nutrition
2003;133:405-410, 411-417.
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