An individual's diet is the sum of food and drink that one habitually consumes. Dieting is the practice of attempting to achieve or maintain a certain weight through diet. People's dietary choices are often affected by a variety of factors, including ethical and religious beliefs, clinical need, or a desire to control weight. Not all diets are considered healthy. Some people follow unhealthy diets through habit, rather than through a conscious choice to eat unhealthily. Terms applied to such eating habits include "junk food diet" and "Western diet". Many diets are considered by clinicians to pose significant health risks and minimal long-term benefit. This is particularly true of "crash" or "fad" diets – short-term, weight-loss plans that involve drastic changes to a person's normal eating habits. Only diets covered on Wikipedia are listed under alphabetically sorted headings.

Belief-based diets

Some people's dietary choices are influenced by their religious, spiritual or philosophical beliefs.

Calorie and weight control diets

A desire to lose weight is a common motivation to change dietary habits, as is a desire to maintain an existing weight. Many weight loss diets are considered by some to entail varying degrees of health risk, and some are not widely considered to be effective. This is especially true of "crash" or "fad" diets. Many of the diets listed below could fall into more than one subcategory. Where this is the case, it is noted in that diet's entry.

Low-calorie diets

Very low calorie diets

A very low calorie diet is consuming fewer than 800 calories per day. Such diets are normally followed under the supervision of a doctor. Zero-calorie diets are also included.

Low-carbohydrate diets

Low-fat diets

Crash diets

Crash diets are very-low-calorie diets used for the purpose of very fast weight loss. They describe diet plans that involve making extreme, rapid changes to food consumption, but are also used as disparaging terms for common eating habits which are considered unhealthy. This diet is dangerous and can lead to sudden death when not done in a medically supervised setting. Several diets listed here are weight-loss diets which would also fit into other sections of this list. Where this is the case, it will be noted in that diet's entry.

Detox diets

Detox diets involve either not consuming or attempting to flush out substances that are considered unhelpful or harmful. Examples include restricting food consumption to foods without colorings or preservatives, taking supplements, or drinking large amounts of water. The latter practice in particular has drawn criticism, as drinking significantly more water than recommended levels can cause hyponatremia. There is no scientific evidence of any benefit from detox diets, and so they are considered to be pseudoscientific.

Diets followed for medical reasons

People's dietary choices are sometimes affected by intolerance or allergy to certain types of food. There are also dietary patterns that might be recommended, prescribed or administered by medical professionals for people with specific medical needs.

Fad diets

A fad diet is a diet that is popular for a time, similar to fads in fashion, without being a standard dietary recommendation, and often promising unreasonably fast weight loss or nonsensical health improvements. There is no single definition of what a fad diet is, encompassing a variety of diets with different approaches and evidence bases, and thus different outcomes, advantages and disadvantages, and it is ever-changing. Generally, fad diets promise short-term changes with little effort, and thus may lack educating consumers about whole-diet, whole lifestyle changes necessary for sustainable health benefits. Fad diets are often promoted with exaggerated claims, such as rapid weight loss of more than 1 kg/week or improving health by "detoxification", or even dangerous claims. Since the "fad" qualification varies over time, social, cultural and subjective view, this list cannot be exhaustive, and fad diets may continue or stop being fads, such as the Mediterranean diet. Some of them have therapeutic indications, such as epilepsy or obesity, and there is no one-size-fits-all diet that would be a panacea for everyone to lose weight or look better. Dieticians are a regulated profession that can distinguish nutritionally sound diets from unhealthy ones.

Food-specific diets

Low-carbohydrate / high-fat diets

High-carbohydrate / low-fat diets

Liquid diets

Fasting

Detoxifying

Other fad diets

Vegetarian diets

A vegetarian diet is one which excludes meat. Vegetarians also avoid food containing by-products of animal slaughter, such as animal-derived rennet and gelatin.

Semi-vegetarian diets

Other diets