Date of Award

9-2010

Degree Name

MS in Agriculture - Food Science and Nutrition

Department

Food Science and Nutrition

Advisor

Louise Berner, Ph.D.

Abstract

Sarcopenia is a growing health problem in this country as more Americans are living well into old age. It has been thought that a higher protein intake may be related to greater lean muscle mass as well as greater muscular strength and physical functioning. The purpose of this research was to examine protein intake and its relationship to lean body mass and physical functioning in a nationally representative sample of U.S. adults.

This research used cross-sectional data from the NHANES 2003-2004 to examine the relationship between protein intake, as an average from two 24h recalls, and dual X-ray absorptiometry (DXA) lean body mass measures. Additionally, these lean body mass measures were examined as predictive of Physical Limitation Score (PLS), an index created from self-reported difficulty in performing basic activities of daily living.

Protein intake was examined as total grams of intake, a percentage of total daily energy and as a percent contributed by animal foods. The lean body mass measures used in this analysis included: total lean mass, appendicular lean mass, muscle mass index [lean mass / height (m2)], appendicular lean mass [appendicular lean mass / height (m2)] and percent lean body mass. Questions used to create the self-reported index of functioning, the Physical Limitation Score (PLS), included difficulty in independently: walking ¼ mile, walking up ten stairs without resting, lifting and carrying 10lbs and standing from an armless straight chair.

It was found that protein intake significantly, positively predicted lean body mass in select age-gender groups, while more often in men than in women. Total grams of protein intake positively predicted total and appendicular muscle mass index in men ages 19-50 (p-value <0.05), appendicular muscle mass index in men ages 51-70 (p-value 0.038) and percent lean mass in men 71+ years (p-value 0.026). Protein as a percent of energy was a significant, positive predictor of appendicular lean mass in men 19-50 (p-value 0.048), muscle mass index in women 19-50 (p-value 0.007), appendicular muscle mass index in women 19-50 (p-value 0.024) and percent lean mass in men 71+ years (p-value 0.019). Protein as a percent of energy was a significant negative predictor of percent lean mass in older women 71+ years (p-value 0.046). Protein as a percent contributed by animal foods was not a significant predictor of lean mass in any age-gender group.

It was also found that Physical Limitation Score (PLS) was surprisingly positively predicted by total and appendicular lean and total and appendicular muscle mass index in nearly all age-gender groups (p-value <0.05) or at least moderately, positively predicted by these (p-value <0.10), meaning that having a greater amount of lean mass predicted greater physical limitation. The only exception was percent lean mass, which was a significant negative predictor of PLS in men and women 60-70 years (p-value <0.05). In this case, a higher percent lean mass was associated with less physical limitation. Additional follow-up analyses revealed that total body fat mass (kg) and percent body fat were significant positive predictors of PLS in most age-gender groups (p-value <0.05), indicating that higher amounts of body fat predicted greater self-reported limitation.

Protein expressed as total grams per day or as a percent of total daily energy were generally significant or marginally significant predictors of lean mass in men of all ages but not often in women while protein as a percent contributed by animal foods was not found to be a significant predictor in any age-gender group. Total lean mass, total fat mass and total percent body fat were generally significant positive predictors of physical limitation, calling into question the functional implications of body composition in an older population. Results suggest that in older adults, excess body fat may be a stronger predictor of physical limitation than low lean muscle mass.

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