A healthy diet contains a balance of food groups and all the nutrients necessary to promote good health. Human nutrition is enormously complex and a healthy diet may vary widely according to an individual's genetic makeup, environment, and health.

Healthy eating is the practice of making choices about what and/or how much one eats with the intention of improving or maintaining good health. Typically, this means following recommendations for a healthy diet.

The concept of healthy eating is primarily a problem in rich countries where the lifestyle includes a modicum of outdoor physical activities, high but not always high-quality food consumption, and a trend towards industrially-produced foods instead of locally-sourced, locally-prepared meals. The article below discusses the recommendations for most citizens of such countries, written from an admittedly developed world point of view. Unfortunately, the main food problems for most of the people in the planet are lack thereof or malnutrition.

Generally, a healthy diet will include:

1. Sufficient calories to maintain a person's metabolic and activity needs, but not so excessive as to result in fat storage greater than roughly 12% of body mass[1]
2. Sufficient fat, consisting mostly of mono- and polyunsaturated fats (avoiding saturated and "trans" fats) and with a balance of omega-6 and long-chain omega-3 lipids
3. Sufficient essential amino acids ("complete protein") to provide cellular replenishment and transport proteins
4. Essential micronutrients such as vitamins and certain minerals
5. Avoiding directly poisonous (e.g. heavy metals) and carcinogenic (e.g. benzene) substances
6. Avoiding foods contaminated by human pathogens (e.g. e. coli, tapeworm eggs)
7. Avoiding chronic high doses of certain foods that are benign or beneficial in small or occasional doses, such as
   • foods or substances with directly toxic properties if chronically ingested at high doses (e.g. chickpeas, ethyl alcohol, Vitamin A)
   • foods that may interfere at high doses with other body processes (e.g. table salt)
   • foods that may burden or exhaust normal functions (especially refined carbohydrates eaten without adequate dietary fiber)

In specific individuals, ingesting foods containing natural allergens (e.g. peanuts, shellfood) or drug-induced allergens (e.g. tyramine for a person taking an MAO inhibitor) may be life-threatening.