Diet plays a critical role in shaping the health and well-being of both individuals and populations, and unhealthy diets are a major risk factor for disease and disability.
Healthy diets help to protect against malnutrition in all its forms, as well as noncommunicable diseases (NCDs), including diabetes, heart disease, stroke and cancer.
Healthy dietary practices start early in life – breastfeeding fosters healthy growth and improves cognitive development.
Dietary behaviours and preferences established in childhood and adolescence often extend into adulthood.
Healthy diets come in many forms, but the four core principles of adequacy, balance, moderation and diversity should be the foundation of any healthy diet.
A diet must also be safe to be healthy, i.e. free from microbial and chemical contaminants.
A variety of minimally processed and unprocessed foods low in unhealthy fats, free sugars and sodium are the foundation of any healthy diet.

Population, in human biology, the whole number of inhabitants occupying an area (such as a country or the world) and continually being modified by increases (births and immigrations) and losses (deaths and emigrations). As with any biological population, the size of a human population is limited by the supply of food, the effect of diseases, and other environmental factors. Human populations are further affected by social customs governing reproduction and by the technological developments, especially in medicine and public health, that have reduced mortality and extended the life span