Understanding how to maintain independence and prevent disability in older persons represents a priority in aging research. Although undernutrition is considered as a putative and potentially modifiable factor contributing to decline in physical function with aging, there is a lack of empirical evidence of its effect on consequent decline in muscle strength and physical function. Furthermore, whether physiological factors such as ghrelin, leptin and inflammatory markers may affect dietary intake in older persons is unknown. The aim of this dissertation was to address this gap in knowledge by examining the following hypotheses: 1) a low intake of protein is associated with subsequent reduction in muscle strength; 2) a low concentration of nutrients is associated with subsequent decline in physical function; 3) concentrations of ghrelin, leptin, and inflammatory markers are associated with reduced dietary intake. To test these hypotheses, we used a population-based, NIH-funded epidemiological study involving over 1100 persons aged >65 years living in Tuscany, Italy. We found that selectively in participants with high levels of C-reactive protein, Interleukin-6 and Tumor Necrosis Factor-?, lower protein intake was associated with a greater decline in muscle strength (Beta for CRP=0.020, p=0.003). Furthermore, we demonstrated that a low concentration of vitamin E was significantly associated with subsequent decline in physical function (odds ratio=1.62; 95% confidence interval=1.11-2.36; p=0.01). A classification and regression tree analysis showed that among persons aged 70 to 80 years, the strongest predictor of decline in physical function was a vitamin E concentration < 32 umol/L (p=60%). Finally, we found that a high concentration of leptin was significantly associated with accelerated decline in energy intake (Beta=-38.0 kcal; p=0.039), and the effect of inflammatory markers on energy intake depended on sex (Beta for CRP(log)*sex=70.0, p=.020). This is the first population-based, longitudinal study on the effect of poor nutrition on decline in muscle strength and physical function, and on the effect of ghrelin, leptin, and inflammatory markers on dietary intake. This study provides empirical evidence that poor nutrition plays an important role in the decline in muscle strength and physical function in older persons and, consequently, may contribute to the disablement process.