Public health and nutrition. Until the mid of the 20th century, the major cause of death was infectious disease. With the progress of medicine, infectious diseases are now almost eradicated in developed countries. Hunger lifespans in an aging population have seen the emergence of chronic and degenerative diseases such as diabetes, cardiovascular disease and osteoporosis. Those diseases are linked to both genetic predisposition and environmental factors such as lifestyle and diet. Among the environmental factors, food plays an important role. Hence, from a public health point of view, ensuring an optimal food intake, in quantity and quality, contributes to the prevention of some of the most deadly and costly diseases. Scientific studies that evaluate the requirements of every type of population. Based on those studies, public health agencies publish recommendations in each population for every nutrient. Public health problems differ depending upon the countries and populations considered. If there is not enough food, diseases like marassanus develop. Conversely, if there is too much food, obesity develops. During those recommendations is not straightforward. There are some critical times of life when it is important to ensure an optimal nutrition. For example, perinatal nutrition has lifelong consequences on weight management and allergies. Also, the impact of most nutritional interventions is not immediate. Human has to be considered through all of life and early age nutrition can have a great effect on aging. As an example, a deficiency in calcium and vitamin D during childhood and adolescence leads to osteoporosis dozens of years later. Beyond the physiological aspect of the recommendations which is to fulfill the bodily requirements, there is a behavioral question. Indeed, now that the requirements are well defined, the challenge for public health actors is to improve the eating behavior of the population. National communication programs promoting the consumption of fruits and vegetables or encouraging physical activity are a good example of public health actions to improve the behavior of a population.