Healthy nutrition

A healthy diet is one that helps to maintain or improve overall health.
A healthy diet provides the body with essential nutrition: fluid, adequate essential amino acids from protein,essential fatty acids, vitamins, minerals, anti-oxidants, fibre and adequate calories. The requirements for a healthy diet can be met from a variety of plant-based and animal-based foods, although a non-animal source of vitamin B12 is needed for those following a vegan diet. A healthy diet supports energy needs and provides for human nutrition without exposure to toxicity or excessive weight gain from consuming more calories than the body requires. A healthy diet, in addition to exercise, is thought to be important for lowering health risks, such as obesity, heart disease, type 2 diabetes, hypertension and cancer.
Various nutrition guides are published by medical and governmental institutions to educate individuals on what they should be eating to promote health. Nutrition facts labels are also mandatory in some countries to allow consumers to choose between foods based on the components relevant to health.
The idea of dietary therapy (using dietary choices to maintain health and improve poor health) is quite old and thus has both modern scientific forms (medical nutrition therapy) and prescientific forms (such as dietary therapy in traditional Chinese medicine).
Mainstream science
Healthy eating is simple, according to Marion Nestle, who expresses the mainstream view among scientists who study nutrition:
The basic principles of good diets are so simple that I can summarize them in just ten words: eat less, move more, eat lots of fruits and vegetables. For additional clarification, a five-word modifier helps: go easy on junk foods. Follow these precepts and you will go a long way toward preventing the major diseases of our overfed society—coronary heart disease, certain cancers, diabetes, stroke, osteoporosis, and a host of others.... These precepts constitute the bottom line of what seem to be the far more complicated dietary recommendations of many health organizations and national and international governments—the forty-one “key recommendations” of the 2005 Dietary Guidelines, for example. ... Although you may feel as though advice about nutrition is constantly changing, the basic ideas behind my four precepts have not changed in half a century. And they leave plenty of room for enjoying the pleasures of food.