The effects of a two‐year randomized, controlled trial of whey protein supplementation on bone structure, IGF‐1, and urinary calcium excretion in older postmenopausal women
What this study found
Overall, 30 g/day whey protein increased serum IGF-1 but did not improve or worsen bone mass or strength over 2 years in this protein-replete population. Serum IGF-1 was higher in the protein group at year 1 by 7.3% ± 2.5% (p = .004) and at year 2 by 8.0% ± 3.3% (p = .016). There were no group-by-time interactions for hip bone variables or femoral neck engineering strength, and no between-group differences in changes in bone density or strength. Twenty-four-hour urinary calcium excretion increased over time in both groups at 1 year, and at 2 years it was 13.4% ± 7.3% higher than placebo in…
- Study & population
- Randomized controlled trial in healthy, ambulant postmenopausal women aged 70-80 years from metropolitan Perth, Western Australia.
- Intervention
- The active intervention was a daily 250-mL oral skim milk-based whey protein drink, reconstituted from powder to provide 30 g protein, 600 mg calcium, and 3.2 kJ/mL.
- Key limitation
- Findings come from healthy older women with relatively high baseline protein intake, limiting generalizability to protein-deficient or other populations.
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Open PDFOriginal abstract
The effects of dietary protein on bone structure and metabolism have been controversial, with evidence for and against beneficial effects. Because no long‐term randomized, controlled studies have been performed, a two‐year study of protein supplementation in 219 healthy ambulant women aged 70 to 80 years was undertaken. Participants were randomized to either a high‐protein drink containing 30 g of whey protein (n = 109) or a placebo drink identical in energy content, appearance, and taste containing 2.1 g of protein (n = 110). Both drinks provided 600 mg of calcium. Dual‐energy X‐ray absorptiometric (DXA) hip areal bone mineral density (aBMD), 24‐hour urinary calcium excretion, and serum insulin‐like growth factor 1 (IGF‐1) were measured at baseline and at 1 and 2 years. Quantitative computed tomographic (QCT) hip volumetric bone mineral density (vBMD) and a femoral neck engineering strength analysis were undertaken at baseline and at 2 years. Baseline average protein intake was 1.1 g/kg of body weight per day. There was a significant decrease in hip DXA aBMD and QCT vBMD over 2 years with no between‐group differences. Femoral neck strength was unchanged in either group over time. The 24‐hour urinary calcium excretion increased significantly from baseline in both groups at 1 year but returned to baseline in the placebo group at 2 years, at which time the protein group had a marginally higher value. Compared with the placebo group, the protein group had significantly higher serum IGF‐1 level at 1 and 2 years (7.3% to 8.0%, p < .05). Our study showed that in protein‐replete healthy ambulant women, 30 g of extra protein increased IGF‐1 but did not have beneficial or deleterious effects on bone mass or strength. The effect of protein supplementation in populations with low dietary protein intake requires urgent attention. © 2011 American Society for Bone and Mineral Research