The purpose of this study is to determine whether consuming additional protein during calorie restriction induced weight loss has beneficial or harmful effects on multi-organ (liver, muscle, adipose tissue) insulin sensitivity, colonocyte proliferation rates, the gut microbiome, muscle mass and function, and bone mineral density in obese, postmenopausal women.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
NONE
Enrollment
75
Goal of 8 to 10% weight loss while consuming the recommended daily allowance of protein (i.e, 0.8 grams of protein per kg body weight per day).
Goal of 8 to 10% weight loss while consuming 150% of the recommended daily allowance of protein (i.e., 1.2 grams of protein per kg body weight per day).
Washington University School of Medicine
St Louis, Missouri, United States
Change in muscle volume
Thigh muscle volume will be measured by magnetic resonance imaging (MRI)
Time frame: Baseline and at 10% weight loss in calorie restriction groups and ~6 to 7 months in the weight maintenance group
Change in muscle strength
Muscle strength will be evaluated by administering maximum one repetition strength and isokinetic strength tests.
Time frame: Baseline and at 10% weight loss in calorie restriction groups and ~6 to 7 months in the weight maintenance group
Changes in bone mineral density and bone mineral content
Total bone mass and total body and regional bone mineral density will be evaluated by using dual X-ray energy absorptiometry (DXA).
Time frame: Baseline and at 10% weight loss in calorie restriction groups and ~6 to 7 months in the weight maintenance group
Change in insulin sensitivity
Insulin sensitivity (glucose rate of disappearance \[Rd\] during a hyperinsulinemic-euglycemic clamp procedure) will be evaluated in a subset of 10 participants per group because power analysis has determined that this number is sufficient to detect a 25% difference between groups assuming 80% power, an alpha value of 0.05 and an average baseline insulin-stimulated glucose Rd of 2,590 ± 492 µmol/min, the average ± SD insulin stimulated glucose Rd the investigators have measured during the past 20 y in obese subjects. In the investigators' experience (Kirk et al., 2009 and Magkos et al., 2016), the weight loss induced increase in insulin stimulated glucose Rd is \~50%.
Time frame: Baseline and at 10% weight loss in calorie restriction groups and ~6 to 7 months in the weight maintenance group
Change in muscle protein metabolism
Rates of muscle protein synthesis, breakdown and net protein balance will be assessed during postabsorptive conditions and when insulin and/or amino acid concentrations are elevated.
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Time frame: Baseline and at 5% weight loss in the calorie restriction groups and after ~3 months in the weight maintenance group
Change in bacterial populations found in the stool
Time frame: Baseline and at 10% weight loss in calorie restriction groups and ~6 to 7 months in the weight maintenance group
Change in cell proliferation (growth) rates in the colon
Colon cell proliferation rates will be determined using stable isotope labelled tracer methods in conjunction with sigmoid colon biopsy samples
Time frame: Baseline and at 10% weight loss in calorie restriction groups and ~6 to 7 months in the weight maintenance group
Determine the acute effect of whey protein ingestion on skeletal muscle insulin sensitivity
Insulin sensitivity will be evaluated using the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotope labeled tracer infusions
Time frame: Prior to starting the weight loss or maintenance intervention
Determine the acute effect of whey protein ingestion on muscle protein metabolism
Rates of muscle protein synthesis, breakdown and net protein balance will be assessed using stable isotope labeled tracer methods during postabsorptive conditions and during insulin infusion with or without whey protein ingestion
Time frame: Prior to starting the weight loss or maintenance intervention