new study leads support to protein
supplementation.
Diets low in protein lead to increases in
sex hormone-binding globulin in men, potentially reducing the availability
of testosterone and causing loss of muscle mass, red cell mass and bone
density, according to a report in the January issue of The Journal of
Clinical Endocrinology and Metabolism.
The new finding provides more evidence that
high-quality protein supplementation can improve health, maintain muscle
mass, and enhance quality of life.
Dr. Longcope and colleagues from New
England Research Institutes, in Watertown, examined the correlates of sex
hormone-binding globulin levels in 1,552 men, ages 40 to 70 years, who
were enrolled in the Massachusetts Male Aging Study.
After accounting for sex hormone levels,
the team found that age and body mass index were strong determinants of
sex hormone-binding globulin levels in the men. In addition, protein and
fiber intake were significant contributors to these levels.
The study results suggest that the natural
reduction in protein intake with age, and perhaps even the tendency to eat
less red meat for health reasons, could result in lower concentrations
of active (unbound) testosterone in men. The decrease in bioavailable
or free testosterone can result in declines in sexual function, muscle,
red cell mass, and contribute to the loss of bone density.
The new data also suggest the converse,
that a high-protein diet could increase bioavailable (free) testosterone
and potentially "...mitigate the effects of the age-related decrease
in that hormone," the researchers observe. Further studies will be
needed to test this hypothesis, they say.
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