Optimizing Protein Intake in Older Americans With Mobility Limitations (OPTIMen)

• Change in lean body mass as measured by dual energy X-ray absorptiometry (DXA) [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  Primary outcome is change in lean body mass, measured by dual energy X-ray absorptiometry (DXA)
  
  

• Tests of Muscle Performance [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  (1) Maximal voluntary strength measured by 1-repetition maximum method in leg press; (2) Maximal voluntary strength in chest press; this exercise was chosen because it involves the large muscle groups of the upper extremities; and (3) Power of hip and knee extension by Bassey's leg rig.
  
  
• Tests of Physical Function and Task-Specific Performance [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  (1) 6-min walking distance and speed; (2) Stair-climbing power and speed +/- 20% load carry; and (3) 50-meter timed walk + 20% load carry.
  
  
• Self-reported Physical Function [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  Physical function domain of the Medical Outcomes Study Short Form-36 (SF-36).
  
  
• Sense of Well-Being, Fatigue and Affectivity Balance [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  Psychological Well Being Index, FACIT-1 Fatigue scale, and Derogatis Affective Balance Scale (DABS) respectively.
  
  

The recommended dietary allowance (RDA) for protein, set at 0.8 grams/kg/day for adult men and women, has engendered debate and many experts advocate protein intakes substantially above the RDA to help maintain muscle anabolism in older individuals. It is not known whether increasing protein intake in older Americans, whose current intake is below the RDA, increases skeletal muscle mass, muscle performance and physical function.

Our first aim is to determine whether administration of 1.3 g/kg/day of protein, compared to the RDA (0.8 g/kg/day), will result in greater improvements in lean body mass, maximal voluntary muscle strength and power, and self-reported and performance-based measures of physical function in older men. Our second aim is to determine whether the gains in lean body mass, maximal voluntary strength and self-reported and performance-based measures of physical function during testosterone administration are greater with 1.3 g protein than with the RDA in older men on a eucaloric diet.

We will conduct a randomized, placebo-controlled, double-blind trial using a 2 X 2 factorial design. Community dwelling men, 65 years or older, who have self-reported mobility limitation, a daily protein intake of <0.8 g/kg/day and no contraindications for testosterone therapy, will be randomly assigned to one of four groups: placebo injections plus protein 0.8 g/kg/day; placebo injections plus protein 1.3 g/kg/day; testosterone enanthate 100 mg weekly plus protein 0.8 g/kg/day; testosterone enanthate 100 mg weekly plus protein 1.3 g/kg/day. Treatment duration will be 6 months. The primary outcome is change in lean body mass from baseline to 6 months, measured by dual energy X-ray absorptiometry. Secondary outcomes include change in maximal voluntary strength in leg and chest press exercises, leg power, self-reported (physical function domain of SF-36) and performance-based measures of physical function (6-min walking distance and speed, stair climbing power, and load carrying), fatigue, well-being and affectivity balance. Safety measures include urinary calcium excretion, hematocrit, prostate specific antigen (PSA) and prostate examination.