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Dieting is the practice or habit of eating (and drinking) in a regulated fashion, usually with the aim of losing weight. It is also used in some cases to gain weight or to regulate the amounts of certain nutrients entering the body. It usually involves a non-traditional diet.

History of dieting

The practice of dieting in order to lose weight is ancient in its origins. Throughout the 17th and 18th centuries, physicians and patients regulated their food carefully, in order to prevent disease. The scientific classification of foods was broken down into proteins, carbohydrates, starches and lipids. Doctors and scientists began experimenting with targeted diets in the 19th century.

William Banting is one of the first people known to have successfully lost weight by dieting, circa 1863, by targeting carbohydrates. (The low carbohydrate diet, marketed today as the Atkins Diet, remains popular today.)

What is not dieting

Certain religions, such as Judaism, Hinduism and Islam, impose strict restrictions on food choices and preparation. These restrictions, however, are not usually considered "dieting."

Vegetarianism is usually not considered "dieting," as it is most often adopted for religious, spiritual or ethical reasons, or in some cases because other food choices are not available. In other cases the motivation is a simple dislike of meat.

Anorexia nervosa and bulimia, which are psychological and neurological disorders that cause victims to endanger their lives with calorie restriction, must not be confused with dieting.

Dieting techniques

Most typically, "dieting" means eating in a carefully planned way in an attempt to reduce excess body fat and decrease bodily measurements, such as clothing size.

There exist a (sometimes confusing) multitude of weight loss techniques, many of which are ineffective. What works for one person will not necessarily work for another, due to metabolic differences and lifestyle factors.

Scientific principles surrounding dieting

Successful weight loss diet is all about energy in versus energy out. If a person takes in less food energy than he or she expends over a period of time, the person may burn fat and subsequently lose weight.

Diets affect the energy in component of the energy balance by limiting or altering the distribution of foods. Techniques that affect the appetite can limit energy intake by affecting the desire to overeat. This can be attempted by focusing on foods that are filling, through the use of certain appetite-suppressing drugs, or through activities such as mild exercise, that affect appetite. Other techniques address habitual or emotional eating.

Affecting the energy out component is the focus of fitness and exercise programs. These might also be included in a comprehensive "diet."

Dieting in order to lose weight does just that — you lose weight, water, and some fat and muscle. Since muscles are denser, you lose a lot of weight, but little in size. Fat is bulkier, so a three pound fat loss can cause a size loss.

To lose a pound of fat, one must create a caloric deficit of approximately 3,500 calories (32,000 kJ per kilogram of fat); therefore, if a person creates a deficit of 500 calories (2,100 kJ) per day, the person will lose approximately 1 pound of fat per week (2,300 kJ per day to lose 0.5 kg in a week).

Muscle loss during weight loss can be restricted by regularly lifting weights and by a high protein intake. (It is said that 0.8 to 1.0 g of protein per pound of body weight (1.8 to 2.2 g/kg) per day is sufficient.)

Weight loss groups

There exist both profit-oriented and non-profit weight loss organizations who assist people in their weight loss efforts. (Examples of the former include Weight Watchers and Jenny Craig; examples of the latter include Overeaters Anonymous and a multitude of non-branded support groups run by local churches, hospitals, or like-minded individuals.) These organizations' customs and practices differ widely, but most all of them leverage the power of group meetings with regards to counseling, emotional support, problem-solving, and the passing along of useful information. Some advocate certain prepared food or special menus, while others train how to make healthy choices from menus and while grocery-shopping.

Fad diets

Many 'fad' diets become widely popular for a short period of time, only to fade out. Although some fade from popularity due to being ineffective, some merely lose the public's interest. Judging their nutritional merit can be especially difficult given that most diet proponents locate medical professionals to back up their work. Examples of such fads include the grapefruit diet, low-fat diets, and Atkins.

Many fad diets advocate a specific technique (such as eliminating a certain food, or eating only certain combinations of foods) in conjunction with the basic idea of balancing energy in versus energy out, the goal being to accelerate weight loss. Some ignore traditional science altogether.

Grapefruit diet

On the grapefruit diet, the consumption of grapefruit with each meal was said to increase the metabolic rate, burning fat and enabling rapid weight loss. The grapefruit diet was eventually found to be entirely ineffective.

Low-fat diets

Low-fat diets were popular during the 1980s and 1990s, encouraging people to eat foods low in fat (or without fat altogether) and instead eat foods high in carbohydrates. The diet worked on the principle that of the three main macro-nutrients (fat, carbohydrates and protein), only fat was the one which would cause weight-gain. This failed as people ended up eating excessive amounts of low-fat foods rich in refined carbohydrates such as sugar. Some low-fat dieters even gained weight due to the calories from the carbohydrates.


Atkins encourages limited carbohydrate intake, and consuming more meats, nuts, unsweetened fruits, berries and green vegetables. This causes rapid weight loss for many people, although it continues to be disputed whether this is due to a metabolic advantage of ketosis, as Atkins claimed. Some of the initial rapid weight loss is due to depletion of glycogen stores in the liver. Glycogen must be associated with several times its weight of water in the body. Low carbohydrate diets have been shown to reduce the fasting levels of triglycerides. Elevated triglycerides are a demonstrated risk factor for heart disease and also account for part of the risk of low density cholesterol due to their associated worse particle size profile. Any successful diet for losing weight will cause some ketosis, since ketones are produced when the body is using fat energy to synthesize glucose (gluconeogenesis) during the long overnight fast (sleep). Elevated levels of fasting triglycerides (TGs) are the product of de novo lipogenesis (synthesis of new fats) from glucose substrate. If the liver was engaged in gluconeogenesis from fat, and synthesizing fat from glucose at the same time, this would be a futile cycle, and a fantastic way to waste energy and lose weight. For most of human history, it has been important to survival to avoid such inefficiency, so the body switches modes to avoid this futile cycle. This explains the dramatic reductions in fasting TGs seen in many low carbohydrate dieters.

Medical diets

Medical conditions often require the use of a special diet that either contains or lacks certain chemicals. For example, a person who has diabetes is often on a diet designed to carefully regulate their blood sugar level, sufferers of celiac disease must follow a gluten-free diet, the lactose-intolerant omit milk and dairy products, and people with kidney disease must follow a strict low-sodium diet to ease the strain on their kidneys.

Treatment for mild hypertension includes a diet rich in fruits, vegetables, and fat-free dairy foods, and low in fat and sodium, to lower blood pressure.

Vegetarian diet

As noted above, while many vegetarians and vegans adopt their diet for religious or ethical reasons, there is a growing body of evidence that vegetarian diets can prevent obesity and lower disease risks.

According to the American Dietetic Association, "Vegetarians have been reported to have lower body mass indices than nonvegetarians, as well as lower rates of death from ischemic heart disease; vegetarians also show lower blood cholesterol levels; lower blood pressure; and lower rates of hypertension, type 2 diabetes, and prostate and colon cancer." (source: American Dietetic Association. 2003. Position paper on vegetarian diets. J Am Diet Assoc. 103:748-765.)

As for weight loss, vegans on average weigh 10% less than non-vegetarians (source: Davis, B. and Melina, V. 2000. Becoming Vegan. pg. 22), and in a year-long study comparing Dean Ornish's vegetarian diet to Weight Watchers, The Zone Diet, and The Atkins Diet, Dean Ornish's diet showed the most weight-loss. (source: Dansinger, M.L., Gleason, J. L., Griffith, J.L., et al., "One Year Effectiveness of the Atkins, Ornish, Weight Watchers, and Zone Diets in Decreasing Body Weight and Heart Disease Risk", Presented at the American Heart Association Scientific Sessions November 12, 2003 in Orlando, Florida.)

Very Low Calorie Diets

The Very Low Calorie Diet, or VLCD, is a special diet to be undertaken with medical supervision. It offers rapid fat loss but can be dangerous. It consists of the consumption of a special powder mixed in with 200-300 ml of water to be taken three times a day. The drink, similar to a milkshake, provides 1914 kJ (456 Cal) of energy per day when consumed at breakfast, lunch and dinner. It contains all necessary vitamins and minerals, although there is a risk of overdosing on selenium if a person consumes more than they should (more than three times per day). VLCDs should only be used for dieting when a person's body mass index exceeds 30. In addition, at least two liters of water must be consumed per day and a person should consider using dietary fiber supplements regularly. Without this, the person risks severe constipation.

VLCDs can be very successful, but only when used over a six- to 12-week period. Because the body is essentially starving, it is burning up its fat stores and lowering its metabolic rate. As soon as the diet ceases and normal food is consumed again, there is an immediate increase in weight. Short-term use of VLCDs (one to four weeks) will have little, if any, benefit for the dieter, as the increase in weight will negate the weight lost in the first place. Once the full course of the diet is finished, it is up to the successful dieter to maintain their current weight via exercise and sensible eating. VLCDs put a great deal of strain on a person's body and should only be undertaken with medical consultation.

Potentially hazardous dieting techniques

Yo-yo dieting is particularly dangerous and ineffective, because it decreases the metabolism, leading to an immediate weight gain once the caloric restrictions are eased.

Many over-the-counter (OTC) and prescribed medications have been proven to be extremely hazardous to the health and consequently withdrawn from sale, so consumers need to be wary.

While anyone can lose weight by fasting (temporarily stopping one's food intake altogether), it is an extremely dangerous practice. When concentration camp survivors, who involuntarily suffered famine as a result of the horrendous living conditions, were examined by doctors, what little weight they had was mostly fat, with practically no muscle.

The reason for the muscle loss is due to the fact that the brain cannot rely on fat for fuel. The brain can only rely on glucose and, to an extent, ketones to fuel itself. Ketones can be made from fats. When carbohydrates are initially limited, the brain still relies heavily on glucose for fuel, but after roughly 2-3 weeks the brain will gradually change its fuel usage to ketones. However, the brain can never use ketones to fuel itself 100%; at least 15% of its fuel must come from glucose. Due to the fact that fasts, very low calorie diets, and low-carbohydrate diets restrict the intake of carbohydrates, glucose must be obtained from some other source. Therefore, the body creates glucose from the available amino acids. These, in turn, are derived from dietary protein or from muscle, if dietary protein is insufficient. For this reason, any low carbohydrate diet is potentially hazardous: if protein intake is not adequate, muscle loss will result. This conversion of amino acids to glucose is called gluconeogenesis.

A very low calorie diet that restricts all carbohydrates and non-essential fats, while providing just enough dietary protein to prevent muscle loss, is termed a protein sparing modified fast or PSMF. This is possible when dietary protein is sufficient to meet the body's glucose needs via gluconeogenesis conversion, thus sparing muscle protein. After a good deal of experimentation, it was found that a protein intake of 1 - 1.5 grams of protein per kilogram of ideal bodyweight prevented the loss of body protein. A somewhat "safer" (although higher calorie) intake of .8 to 1.2 grams of protein per pound of LBM is often recommended, with even greater requirements for active individuals. Thus, a PSMF allows for rapid fat loss due to the severe caloric deficit that is created when nearly all carbohydrates and fats are removed from the diet. As with any VLCD, the PSMF is an extreme dieting technique subject to the same potential hazards: hormonal changes, rapid metabolic slowdown, nutrient deficiencies, and other side effects, and should be used with extreme caution.

The "safest" method of weight loss, to avoid rapid metabolic slowdown and possible muscle loss, is to eat a sensible, healthy diet while moderately decreasing caloric intake, and to increase exercise gradually until weight loss results. A good guideline to follow would be to create a calorie deficit of roughly 20% of normal daily caloric intake (calculate your daily caloric intake). Half of the deficit should be created through diet and the other half through exercise. This should allow one to lose fat, and maintain muscle mass, therefore curbing the metabolic slowdown associated with a reduction in bodyweight. Weight lifting is also a good guideline to follow as it has been shown to cause a response in the body to maintain muscle stores, and even stimulate muscle growth in untrained individuals, while on a caloric deficit.

More information

U.S. government site on dieting

U.K. government site on dieting

Go to home page of nutrition | Sources and Attributions


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