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Effects of a higher protein weight loss diet on body composition, metabolic disease risk and physical function in postmenopausal women

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Title: Effects of a higher protein weight loss diet on body composition, metabolic disease risk and physical function in postmenopausal women
Author(s): Mojtahedi, Mina C.
Director of Research: Evans, Ellen M.
Doctoral Committee Chair(s): Layman, Donald K.
Doctoral Committee Member(s): Evans, Ellen M.; Woods, Jeffrey A.; Georgiadis, John G.
Department / Program: Nutritional Sciences
Discipline: Nutritional Sciences
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): dietary protein body composition physical function weight loss, inflammation postmenopausal women
Abstract: Adverse increases in adiposity and reductions in lean soft tissue (LST) are age related changes in body composition and are linked to an increased risk for metabolic disease and declines in physical function in older women. Higher protein intake under caloric reduced conditions eliciting weight loss may augment fat mass (FM) loss, which can reduce metabolic disease risk; and attenuate LST loss, which may benefit physical function. This study assessed effects of 6 mo weight loss supplemented with powdered protein or placebo on body composition, metabolic disease risk factors and physical function in older obese women. Twenty-six women (64.7±5.8 yrs, BMI 32.5±4.1 kg/m2) were prescribed an energy-restricted diet (1400 kcal/d) and randomly assigned to PRO (n=13; 0.8 g/kg/d of dietary protein plus 45g/d of whey protein isolate supplement, resulting in ~30% of energy intake from protein, 40% of energy from carbohydrate and 30% of energy from fat) or CARB (n=13; 0.8 g/kg/d protein plus 50 g/d of an isocaloric maltodextrin supplement, resulting in ~18% of energy from protein, 52% of energy from carbohydrate and 30% of energy from fat) supplementation. Healthy eating based on the USDA My Pyramid diet education classes were taught by a registered dietitian every 2 weeks. Supervised exercise classes, consisting of flexibility and low to moderate intensity walking on an indoor track, were provided 5 d/wk, of which participants were required to attend 2-3 exercise classes/wk. The main outcome measures included the following: whole body FM and LST with DXA; thigh muscle volume, subcutaneous adipose tissue (SAT), intermuscular adipose tissue (IMAT) with MRI; glucose, insulin, C-reactive protein (CRP) and interleukin-6 (IL-6) from fasting blood samples; knee extension and flexion strength with isokinetic and isometric dynamometry; balance using the Star Excursion Balance Test (SEBT); and physical performance assessed from up and go, chair stand, stair climb and transfer tests. Three-day weighed food diaries were collected at baseline, month 3 and post-intervention, and 7-day pedometer step counts were measured monthly. PRO trended towards greater weight loss (-8.0±6.2%, -4.1±3.6%; p=0.059), had greater reductions in abdominal FM (-14.8±15.0%, -4.1±8.1%; p=0.037) but no significant differences in losses of FM (-15.4±17.8%, -6.1±5.4%; p=0.091), greater reductions in SAT (-18.8±13.5, -7.9±6.9; p=0.024) and IMAT (-9.2±9.4, -1.0±7.7; p=0.028) but no difference in IMAT relative to muscle volume (4.7±5.8, 4.3±8.6; p=0.883) compared to CARB, respectively. No differences were seen in LST changes (-4.0±4.9%, -2.0±4.1%; p=0.414), but PRO had a greater improvement in weight to leg LST ratio (-4.6±3.6, -1.8±2.6; p=0.033), greater reductions in absolute thigh muscle volume (-5.0±3.4, -0.8±3.9; p=0.010) and greater gains in relative thigh muscle volume (10.3±8.8%, 4.5±3.4; p=0.049) compared to CARB. Groups did not differ in changes in metabolic disease risk factors, knee strength, balance or physical performance measures. Change in SAT volume was an independent predictor of % change in CRP explaining 30% of the variance (p=0.021), and change in abdominal fat mass showed a trend towards independently predicting % change in CRP (p=0.057). Changes in weight to leg LST ratio predicted changes in up and go (adjusted r2=0.189, p=0.02); whereas whole body %LST predicted changes in balance (adjusted r2=0.179, p=0.04). Higher protein weight loss diet in older women contributes to more weight loss and optimal changes in body composition compared to a greater carbohydrate regimen. Protein intake does not appear to directly impact changes in metabolic risk factors or physical function; however, changes in abdominal fat and SAT reduce systemic inflammation, and preservation of LST with weight reduction improves balance and physical performance.
Issue Date: 2010-08-31
URI: http://hdl.handle.net/2142/16987
Rights Information: Copyright 2010 Mina Mojtahedi
Date Available in IDEALS: 2010-08-31
2012-09-07
Date Deposited: 2010-08
 

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