Dieting is the practice of
ingesting food in a regulated fashion to achieve a particular objective. In many cases the goal is
weight loss, but some athletes aspire to gain weight (usually in the form of
muscle) and diets can also be used to maintain a stable body weight.
Types of dieting Receiving adequate nutrition through a well-balanced diet is critical during childhood and adolescence. Unless a doctor says otherwise, low-carb, low-fat, or other specialty diets for children who are not heavily obese are unhealthy because they deprive the body of the building blocks of cells (namely energy and lipids in the above examples).
It is especially notable that, as more cultures scrutinize their diets, many improperly educated mothers consider putting their children on restricted diets that actually do more harm than good.
This is extremely deleterious to a young child's health because a full and balanced diet (fats, carbohydrates, protein, vitamins, minerals, fiber, etc.) is needed for growth. In children and young adults In the broadest sense, at least some targeted dieting has clearly existed since prehistoric times for various social, religious, and biological reasons.
See
Luigi Cornaro for a 16th century treatise on dieting. Throughout the 17th and 18th centuries, physicians and patients regulated their food carefully, in order to prevent disease. In the 19th century, as the scientific classification of foods took shape, doctors and scientists began experimenting with targeted diets.
William Banting is one of the first people known to have successfully lost weight by developing a targeted diet, circa
1863, by targeting carbohydrates. The
low carbohydrate diet, sometimes marketed today as the
Atkins Diet, remains popular today.
History of targeted dieting According to the principles of
thermoregulation, humans are
endotherms. We expend energy to maintain our blood temperature at
body temperature, which is about 37 °C (98.6 °F). This is accomplished by metabolism and blood circulation, by shivering to stay warm, and by sweating to stay cool.
In addition to thermoregulation, humans expend energy keeping the vital organs (especially the lungs, heart and brain) functioning. Except when sleeping, our
skeletal muscles are working, typically to maintain upright
posture. The average work done just to stay alive is the
basal metabolic rate, which (for humans) is about 1 watt per kilogram (2.2 lbs) of body mass. Thus, an average man of 75 kilograms (165 lbs) who just rests (or only walks a few steps) burns about 75 watts (continuously), or about 6,500
kilojoules (1,440
Calories) per day or 1 Calorie each minute.
Thermoregulation Physical exercise is an important complement to dieting in securing weight loss.
Aerobic exercise is also an important part of maintaining normal
good health, especially the
muscular strength of the heart. To be useful, aerobic exercise requires maintaining a
target heart rate of above 50 percent of one's
resting heart rate for 30 minutes, at least 3 times a week. Brisk walking can accomplish this.
The ability of a few hours a week of exercise to contribute to weight loss can be somewhat overestimated. To illustrate, consider a 100-kilogram (220 lbs) man who wants to lose 10 kilograms (22 lbs) and assume that he eats just enough to maintain his weight (at rest), so that weight loss can only come from exercise. Those 10 (22 lbs) kilograms converted to work are equivalent to about 350 megajoules. (We use an approximation of the standard 37 kilojoules or 9 Calories per gram of fat.) Now assume that his chosen exercise is stairclimbing and that he is 20 percent efficient at converting chemical energy into mechanical work (this is within measured ranges). To lose the weight, he must ascend 70 kilometers. A man of normal fitness (like him) will be tired after 500 meters of climbing (about 150 flights of stairs), so he needs to exercise every day for 140 days (to reach his target). However, exercise (both aerobic and anaerobic) would increase the Basal Metabolic Rate (BMR) for some time after the workout. This ensures more calorific loss than otherwise estimated.
The minimum safe dietary energy intake (without medical supervision) is 75 percent of that needed to maintain basal metabolism. For our hypothetical 100-kilogram man, that minimum is about 5,700 kilojoules (1,300 calories) per day. By combining daily aerobic exercise with a weight-loss diet, he would be able to lose 10 kilograms in half the time (70 days). Of course, the described regime is more rigorous than would be desirable or advisable for many persons. Therefore, under an effective but more manageable weight-loss program, losing 10 kilograms (about 20 pounds) may take as long as 6 months.
There are also some easy ways for people to exercise, such as walking rather than driving, climbing stairs instead of taking elevators, doing more housework with fewer power tools, or parking their cars farther and walking to school or the office.
Physical exercise It is important to understand the difference between weight loss and fat loss. Weight loss typically involves the loss of fat, water and muscle. A dieter can lose weight without losing much fat. Ideally, overweight people should seek to lose fat and preserve muscle, since muscle burns more calories than fat. Generally, the more muscle mass one has, the higher one's metabolism is, resulting in more calories being burned, even at rest. Since muscles are more dense than fat, muscle loss results in little loss of physical bulk compared with fat loss. To determine whether weight loss is due to fat, various methods of measuring
body fat percentage have been developed.
Muscle loss during weight loss can be restricted by regularly lifting weights (or doing
push-ups and other strength-oriented
calisthenics) and by maintaining sufficient
protein intake. According to the
National Academy of Sciences, the
Dietary Reference Intake for protein is "0.8 grams per kilogram of body weight for adults."
Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their protein intake which is necessary. However, there may be risks involved. According to the
American Heart Association, excessive protein intake may cause liver and kidney problems and may be a
risk factor for
heart disease. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous, however, it has only been shown that these diets are dangerous in individuals who already have kidney and liver problems.
Fat loss versus muscle loss The energy humans get from food is limited by the efficiency of digestion and the efficiency of utilization. The efficiency of digestion is largely dependent on the type of food being eaten. Poorly chewed seeds are poorly digested. Refined sugars and fats are absorbed almost completely. Chewing does not compensate for the calorie content of a food that is eaten; even
celery, which is primarily indigestible
cellulose, contains enough
sugars to easily compensate for the cost of chewing it.
Energy obtained from food Humans require essential nutrients from six broad classes:
proteins,
fats,
vitamin,
dietary minerals, and
water. Essential
amino acids (protein) are required for cell, especially muscle, construction. Essential
fatty acids are required for brain and cell membrane construction.
Any diet that fails to meet minimum nutritional requirements can threaten general health (and physical fitness in particular). If a person is not well enough to be active, weight loss and good quality of life will be unlikely.
The
National Academy of Sciences and the
World Health Organization publish guidelines for dietary intakes of all known essential nutrients.
Sometimes dieters will ingest excessive amounts of vitamin and mineral supplements. While this is usually harmless, some nutrients are dangerous. Men (and women who don't
menstruate) need to be wary of
iron poisoning. Retinol (oil-soluble vitamin A) is toxic in large doses. As a general rule, most people can get the nutrition they need from foods (there are specific exceptions; vegans often need to supplement vitamin B12). In any event, a multivitamin taken once a day will suffice for the majority of the population.
A sensible weight-loss diet is a normal balanced diet; it just comes with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing). Extreme diets may lead to malnutrition, and are less likely to be effective at long-term weight loss in any event.
How the body gets rid of fat 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.
Consumption of low-energy, fiber-rich foods, such as non-starchy vegetables, is effective in obtaining satiation (the feeling of "fullness"). Exercise is also useful in controlling appetite as is drinking water and sleeping. (Extreme physical fatigue, such as experienced by soldiers and mountain climbers, can make eating a difficult chore.)
The use of drugs to control appetite is also common. Stimulants are often taken as a means to suppress (normal, healthy) hunger by people who are dieting. Ephedrine (through facilitating the release of adrenaline and noradrenaline) stimulates the alpha(1)-adrenoreceptor subtype, which is known to act as an
anorectic. L-Phenylalanine, an amino acid found in whey protein powders also has the ability to suppress appetite by increasing the hormone
cholecystokinin (CCK) which sends a satiety signal to the brain.
Psychological aspects of weight-loss dieting There exist both profit-oriented and non-profit weight loss organizations who assist people in their weight loss efforts. An example of the former is
Weight Watchers ; examples of the latter include
Overeaters Anonymous, as well as a multitude of non-branded support groups run by local churches, hospitals, and like-minded individuals.
These organizations' customs and practices differ widely. Some groups are modelled on
twelve-step programs, while others are quite informal. Some groups advocate certain prepared foods or special menus, while others train dieters to make healthy choices from restaurant menus and while grocery-shopping and cooking.
Most groups leverage the power of group meetings to provide counseling, emotional support, problem-solving, and useful information.
Weight loss groups Popular diets (sometimes pejoratively called "fad diets") usually derive their popularity from the
personalities of their proponents. These proponents include "diet
gurus" and celebrity converts. "Diet books" are the primary means of communicating the specifics of popular diets.
Most popular diets experience short-lived popularity, partly because new diet books are continuously being published.
Judging the effectiveness (and nutritional merit) of popular diets can be especially difficult. Diet proponents often locate medical professionals to back up their work. Some diets are so
controversial that they divide the medical community.
Many popular diets advocate the combination of a specific technique (such as eliminating a certain food, or eating only certain combinations of foods) with reduced caloric intake, with the goal being to accelerate weight loss. Others ignore traditional science altogether.
Popular weight-loss 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 general public came to believe, partly due to information from low-fat diet proponents, that carbohydrates were "energy food" and that only fat made people fat. This led to high consumption of low-fat foods high in refined carbohydrates (notably
corn syrup), which may have contributed towards increased weight gain as carbohydrates (particularly refined carbohydrates) have a low
nutrient density and high in
calories. Some low-fat diets like the
Pritikin diet focus on whole grains, vegetables and lean meats.
Low-fat diets Main article: Atkins Nutritional Approach Atkins diet Since the advent of controversial diets such as Atkins, various diets that stress the eating habits of "natural humans" have been developed. The
Paleolithic Diet imitates the way people ate during the
Stone Age. These eating plans include basically natural foods (those not processed by humans). Whereas the Paleolithic Diet excludes milk and grain-foods, The Evolution Diet excludes human-made ingredients such as
partially hydrogenated oils but allows some processed foods such as whole-grain crackers and dairy products. Anthropologists who focus their research on human evolution, however, are quick to point out that the diet of Paleolithic peoples was most likely opportunistic. That is, these early humans would most likely eat whatever edible foods were available at any given moment in that particular area (e.g. vegetables, termites, meat) and not restrict their intake of any food. Until recent human history, starvation has been a far greater threat than over-consumption.
Natural diets 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."
Vegetarians on average weigh 10 percent less than non-vegetarians. And in a year-long study comparing Dean Ornish's vegetarian diet to Weight Watchers, The Zone Diet, and The Atkins Diet, subjects on The Atkins Diet achieved the most weight loss (on average). Strict vegetarian diets like
veganism may result in certain vitamin and mineral deficiencies if attention isn't paid to nutrition.
Vegetarian diet Main article: Weight Watchers Weight Watchers Main article: Very low calorie diet Very low calorie diet Extreme calorie restriction, medication or unusual patterns of eating (i.e. restricting food consumption to a single fruit or meal) can be dangerous.
Dangers Certain medications can be prescribed to assist in weight loss. Some, like
amphetamines, are dangerous now banned for casual weight loss. Others, including those containing
vitamins and
minerals, are not effective for losing weight.
Medications Diuretics induce weight loss through the excretion of water. These medication or
herbs will reduce the amount that a body weighs, but will have no effect on an individual's
body fat. Diuretics can thicken the blood, cause cramping, kidney and liver damage.
Diuretics Stimulants such as
ephedrine (now illegal in the
United States due to an
FDA ban) or
synephrine work to increase the
basal metabolic rate and reduce appetite. Stimulants can cause kidney and liver damage, sudden heart attacks,
addiction, and
ischemic strokes.
Stimulants Main article: Fasting Side effects Body image Crash diet Diet aid Dietitian Food faddism Healthy diet Jenny Craig List of diets National Weight Control Registry Nutritional rating systems Underweight
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