Women and men consuming a low protein diet may be at risk for bone loss. The purpose of this study is to determine whether a daily protein supplement will improve bone health among healthy older adults.

Dietary protein plays an important role in maintaining balanced calcium levels in the body. Protein's impact on skeletal health remains unclear. It is well accepted that increasing dietary protein results in greater excretion of calcium through urine. The excreted calcium is thought to come in part from bone, which would suggest a negative effect on bone health. However, recent studies have found that higher protein intake is, in fact, associated with higher bone mineral density and lower rates of bone loss. The purpose of this study is to determine if a daily protein supplement will improve bone health and hormonal measures of bone metabolism among healthy older men and women who consume low-to-normal levels of dietary protein.

This study will last 18 months. For the duration of the study, participants will be randomly assigned to receive either a 40-gram protein supplement or placebo daily. There will be a total of nine study visits that will occur at screening, study entry, Month 1.5, and every three months thereafter. Dietary records, nutritional counseling, glucose finger stick tests, and questionnaires related to falls, physical activity, habits, and study satisfaction will occur at all study visits. Blood and urine collection, functional testing, and bone mineral density (BMD) testing will occur at selected visits. At Months 0 and 18, half of the participants will undergo a quantitative computed tomography (CT) scan to determine bone mineral density.

Inclusion Criteria:

• Willing to travel to one of the study sites
• Women age 60 years or greater, men age 70 years or greater
• Dietary protein intake level between 0.6 g/kg and 1.0 g/kg at baseline

Exclusion Criteria:

• Active Paget's disease
• Primary hyperparathyroidism or unexplained hypercalcemia
• Untreated hyperthyroidism or hyperthyroidism that has resulted from medical treatment
• Diabetes mellitus type 1
• Cancer diagnosis for solid malignancies (e.g., cancer of the colon, breast,prostate, lungs, lymphocytes) within the 18 months prior to study entry
• Long-term use of chemotherapeutic drugs, aromatase inhibitors, or tamoxifen
• Active treatment for leukemia or multiple myeloma
• Active inflammatory bowel disease
• Life expectancy of less than 2 years
• Current and ongoing use of methotrexate, phenytoin, phenobarbital, or inhaled corticosteroids at a dose of greater than 800 mcg/day
• Use of raloxifene, estrogen, androgen, progesterone, soy isoflavones, oral glucocorticoids, or herbal supplements with estrogenic activity OR a change in dosage of thyroid medications within the 1 year prior to study entry if unwilling to avoid such agents during the duration of the study
• Current use of antiresorptive agents (e.g., calcitonin or bisphosphonates). More information about this criterion can be found in the protocol.
• serum creatinine greater than 1.2 mg/dl
• History of chronic liver disease or evidence of liver disease at screening
• Bilateral hip replacement
• women who have a bone mineral density T-score < -2.5 at either the hip or spine unless they have decided to decline treatment with conventional anti-osteoporotic medications
• Body mass index (BMI) greater than 32 or less than 19
• Use of proton-pump inhibitors taken twice daily
• Fasting glucose level greater than 110 mg/dl
• Serum albumin level less than 3.0 mg/dl
• Kidney stones or history of kidney stones within the 3 years prior to study entry

Healthy older men and women with no known disorders that affect mineral metabolism and not taking drugs that alter skeletal metabolism.

AE data was collected from July 2007 to May 2012

Gastrointestinal adverse events were assessed at times as part of a group of events.

The limitations of this study include the large attrition rate due to the length of the intervention and the difficulty in adhering to 40 grams of protein or placebo powder as a daily supplement.