An individual's diet is the sum of food and drink that he or she 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.
Hallelujah diet: A form of Christian vegetarianism developed in the 1970s. The creators interpret a verse from the Bible as suggesting that Christians should only consume seed bearing plants and fruits.
Hindu and Jain diets: Followers of Hinduism and Jainism often follow lacto-vegetarian diets, based on the principle of Ahimsa (non-harming).
Islamic dietary laws: Muslims follow a diet consisting solely of food that is halal – permissible under Islamic law. The opposite of halal is haraam, food that is Islamically Impermissible. Haraam substances include alcohol, pork, and any meat from an animal which was not killed through the Islamic method of ritual slaughter (Dhabiha).
I-tal: A set of principles which influences the diet of many members of the Rastafari movement. One principle is that natural foods should be consumed. Some Rastafarians interpret I-tal to advocate vegetarianism or veganism.
Kosher diet: Food permissible under Kashrut, the set of Jewish dietary laws, is said to be Kosher. Some foods and food combinations are non-Kosher, and failure to prepare food in accordance with Kashrut can make otherwise permissible foods non-Kosher.
Lacto vegetarianism: A vegetarian diet that includes certain types of dairy, but excludes eggs and foods which contain animal rennet. A common diet among followers of several religions, including Hinduism and Jainism, based on the principle of Ahimsa (non-harming).
Plant-based diet: A broad term to describe diets in which animal products do not form a large proportion of the diet. Under some definitions a plant-based diet is fully vegetarian; under others it is possible to follow a plant-based diet whilst occasionally consuming meat.
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.
Cookie diet: A calorie control diet in which low-fat cookies are eaten to quell hunger, often in place of a meal.
Hacker's diet: A calorie-control diet from The Hacker's Diet by John Walker. The book suggests that the key to reaching and maintaining the desired weight is understanding and carefully monitoring calories consumed and used.
Nutrisystems Diet: The dietary element of the weight-loss plan from Nutrisystem, Inc. Nutrisystem distributes low-calorie meals, with specific ratios of fats, proteins and carbohydrates.
Weight Watchers diet: Foods are assigned points values; dieters can eat any food with a points value provided they stay within their daily points limit.
Atkins diet: A low-carbohydrate diet, populised by nutritionist Robert Atkins in the late-20th and early-21st centuries. Proponents argue that this approach is a more successful way of losing weight than low-calorie diets; critics argue that a low-carb approach poses increased health risks.
Dukan Diet: A multi-step diet based on high protein and limited carbohydrate consumption. It starts with two steps intended to facilitate short term weight loss, followed by two steps intended to consolidate these losses and return to a more balanced long-term diet.
ITG Diet: A 3-step diet based on limiting carbohydrate consumption combined with low fat protein to maintain muscle. The first step is followed to reach the dieter's goal weight while steps two and three focus on returning the body and dieter to a healthy balanced diet for long term weight maintenance.
McDougall's starch diet is a high calorie, high fiber, low fat diet that is based on starches such as potatoes, rice, and beans which excludes all animal foods and added vegetable oils. John A. McDougall draws on historical observation of how many civilizations around the world throughout time have thrived on starch foods.
Crash diet and fad diet are general terms. They describe diet plans which involve making extreme, rapid changes to food consumption, but are also used as disparaging terms for common eating habits which are considered unhealthy. Both types of diet are often considered to pose health risks. Many of the 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.
Beverly Hills Diet: An extreme diet which has only fruits in the first days, gradually increasing the selection of foods up to the sixth week.
Grapefruit diet: A fad diet, intended to facilitate weight loss, in which grapefruit is consumed in large quantities at meal times.
Israeli Army diet: An eight-day diet. Only apples are consumed in the first two days, cheese in the following two days, chicken on days five and six, and salad for the final two days. Despite what the name suggests, the diet is not followed by Israel Defense Forces. It is considered a fad diet.
Junk food diet: A diet largely made up of food considered to be unhealthy, such as high-fat or processed foods.
Subway diet: A crash diet in which a person consumes Subway sandwiches in place of higher calorie fast foods. Made famous by former obese student Jared Fogle, who lost 245 pounds after replacing his meals with Subway sandwiches as part of an effort to lose weight.
Watermelon diet: Liberace and his handlers covered up the entertainer's AIDS diagnosis by publicly attributing his suffered severe weight loss and health problems to anemia brought on by a strict watermelon-only diet; they later reversed those claims to publicize that Liberace was gravely ill from anemia, emphysema and heart disease.
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 colourings or preservatives, taking supplements, or drinking large amounts of water. The latter practise in particular has drawn criticism, as drinking significantly more water than recommended levels can cause hyponatremia.
Juice fasting: A form of detox diet, in which nutrition is obtained solely from fruit and vegetable juices. The health implications of such diets are disputed.
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.
Colon Cancer Diet: Calcium, milk and garlic are thought to help prevent colon cancer. Red meat and processed meat may increase risk.
Diabetic diet: An umbrella term for diets recommended to people with diabetes. There is considerable disagreement in the scientific community as to what sort of diet is best for sufferers.
Healthy kidney diet: This diet is for those impacted with chronic kidney disease, those with only one kidney who have a kidney infection and those who may be suffering from some other kidney failure. This diet is not the dialysis diet  which is something completely different. The healthy kidney diet restricts large amounts of protein which are hard for the kidney to breakdown but especially limits: potassium and phosphorus rich foods and beverages. Liquids are often restricted as well- not forbidden, just less of. 
Ketogenic diet: A high-fat, low-carb diet, in which dietary and body fat is converted into energy. Used as a medical treatment for refractory epilepsy.
Liquid diet: A diet in which only liquids are consumed. May be administered by clinicians for medical reasons, such as after a gastric bypass or to prevent death through starvation from a hunger strike.
Strict Avoidance Diet: Once someone has been diagnosed with a food allergy, being that there is no validated cure yet (2013), they must follow a strict avoidance diet to those specific foods they are allergic to. (i.e. if you have been diagnosed with a peanut, fish, tree nut, ginger allergy you must not consume even the smallest portion of those items or it could evoke a life threatening reaction. Every person reacts differently to different allergens but at any point the reaction could become more severe and it is best to strictly avoid these items.
Dr. Hay diet: Developed by William Howard Hay in the 1920s. Divides foods into separate groups, and suggests that proteins and carbohydrates should not be consumed in the same meal.
Eat-clean diet: Focusses on eating foods without preservatives, and on mixing lean proteins with complex carbohydrates.
Basket of fresh fruit and vegetables grown in Israel
Feingold diet: A diet which attempts to combat hyperactivity by avoiding foods with certain synthetic additives and sweeteners.
Fit for Life diet: The dietary aspect to Fit for Life, a book by Harvey and Marilyn Diamond. Its recommendations include not combining protein and carbohydrates, not drinking water at meal time, and avoiding dairy foods.
Food combining diet: A nutritional approach where certain food types are deliberately consumed together or separately. For instance, some weight control diets suggest that proteins and carbohydrates should not be consumed in the same meal.
Gerson therapy: A form of alternative medicine, the diet is low salt, low fat and vegetarian, and also involves taking specific supplements. It was developed by Max Gerson, who claimed the therapy could cure cancer and chronic, degenerative diseases. These claims have not been scientifically proven, and the American Cancer Society claims that elements of the therapy have caused serious illness and death.
The Graham Diet: A vegetarian diet which promotes whole-wheat flour and discourages the consumption of stimulants such as alcohol and caffeine. Developed by Sylvester Graham in the 19th century.
High-protein diet: A diet in which high quantities of protein are consumed with the intention of building muscle. Not to be confused with low-carb diets, where the intention is to lose weight by restricting carbohydrates.
Sharing of frozen, aged walrus meat among Inuit families.
Inuit diet: Inuit people traditionally consume food that is fished, hunted or gathered locally; predominantly meat and fish.
Jenny Craig: A weight-loss program from Jenny Craig, Inc. It includes weight counselling among other elements. The dietary aspect involves the consumption of pre-packaged food produced by the company.
Low carbon diet: Consuming food which has been produced, prepared and transported with a minimum of associated greenhouse gas emissions. An example of this was explored in the book 100-Mile Diet, in which the authors only consumed food grown within 100 miles of their residence for a year. People who follow this type of diet are sometimes known as locavores.
Paleolithic diet: Can refer either to the eating habits of humans during the Paleolithic era, or of modern dietary plans based on these habits.
Prison loaf: A meal replacement served in some United States prisons to inmates who are not trusted to use cutlery. Its composition varies between institutions and states, but as a replacement for standard food, it is intended to provide inmates with all their dietary needs.