Energy supply from foods and drinks depends upon carbohydrate, protein, lipid and alcohol content. Cells obtain the energy through a complex and integrated system of physico-chemical processes. The energy value of foods is applied for ATP formation, but also for nutrient utilization and turnover. Net energy from foods is expended for basal metabolism, thermic effect of food and physical activity. Total energy expenditure for human beings is displayed in different lists developed by national and international organisms and institutions. Energy balance and body weight are narrowly interrelated as well as body composition, which depends also of age, sex, exercise and neuroendocrine status. Obesity, is known as an excessive deposition of fat for height, and it is associated with cancer, dislipemias, endocrine abnormalities, diabetes, etc. Recent advances suggest that genetic and neuroendocrine factors are more involved in obesity rather than gluttony or sloth as previously reported.