Aging is the combined totality of physiological changes that take place in the human body leading to senescence, the decline of biological functions and of the ability to adapt to metabolic stress. In humans the physiological developments are normally accompanied by psychological and behavioral changes, and other changes, involving social and economic factors, also occur. Physiological changes, such as the slowing down of the metabolism and the occurrence of chronic conditions (chronic obstructive pulmonary disease, bowel diseases, diabetes, cancer, and certain degenerative conditions related to mobility, vision, and cognitive functions) affect metabolism and nutritional needs in this population.