Dieting
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Measuring body weight on a scale

Dieting is the practice of ingesting food in a regulated fashion to achieve or maintain a controlled weight. In most 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

There are several kinds of diets:

• Weight-loss diets are used to treat both the overweight and obese. They restricts the intake of specific types of foods, or restrict intake generally in an attempt to reduce body weight. What works to reduce body weight for one person will not necessarily work for another, due to metabolic differences and lifestyle factors. Also, for a variety of reasons, most people find it difficult to maintain significant weight loss over time — among individuals that have lost 10% or more of body weight, only 20% are able to maintain that weight loss for a full year.^[1]

• Many professional athletes impose weight-gain diets on themselves. American football players may try to "bulk up" through weight-gain diets in order to gain an advantage on the field with a higher mass.

• Individuals who are underweight, such as those recovering from anorexia nervosa or starvation, may adopt weight-gain diets which, unlike those of athletes, have the goal of restoring normal levels of body fat, muscle, and stores of essential nutrients.

In children and young adults

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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). Research shows that putting children on diet foods can be harmful. The brain is unable to learn how to correlate taste with nutritional value, which is why such children may consistently overeat later in life despite adequate nutritional intake. ^[2]

Children who diet could actually be doing worse things for themselves and their bodies. Alison Field from Harvard Medical School stated that "Our study found that dieting was counterproductive- children who dieted gained more, not less, weight than non-dieters." Scott,R.,Jennifer "Dieting Kids May Gain Weight" 12,July,2006^[3] Children who diet tend to develop habits of overeating, or binge eating as a result of attempting to casually diet. It is suggested that children should just attempt to eat healthy instead of trying to casually diet.

Thermoregulation

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.^[4]

In addition to thermoregulation, humans expend energy keeping the vital organs (especially the lungs, heart and brain) functioning. Except when sleeping, 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 of body mass (0.45 W/lb). Thus, an average man of 75 kilograms (165 lb) who just rests (or only walks a few steps) burns about 75 watts (continuously), or about 6,500 kilojoules (1,440 kilocalories) per day or 1 kilocalorie each minute.

Physical exercise

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 50 percent above one's resting heart rate for 30 minutes, at least 3 times a week.^{citation needed} Brisk walking can accomplish this. For example, if the resting heart rate is 70 bpm (beats per minute), the target heart rate would be 105 bpm.

The minimum safe dietary energy intake (without medical supervision) is 75 percent of that needed to maintain basal metabolism.^{citation needed} For a hypothetical 100-kilogram man, that minimum is about 5,700 kilojoules (1,300 kilocalories) 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).

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.

Fat loss versus muscle 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. Approximately 14 kilocalories of fat are burned per pound of muscle 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.^[5] 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.^{citation needed}

Energy obtained from food

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.^{citation needed}

Proper nutrition

Food provides nutrients from six broad classes: proteins, fats, carbohydrates, vitamins, dietary minerals, and water. Carbohydrates are metabolized to provide energy. Proteins provide amino acids, which are required for cell, especially muscle, construction. Essential fatty acids are required for brain and cell membrane construction. Vitamins and trace minerals help maintain proper electrolyte balance and are required for many metabolic processes. Dietary fiber is another food component which influences health even though it is not actually absorbed into the body.

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).

Extreme calorie restriction (fewer calories than 75% of that required for basal metabolic rate), medication or unusual patterns of eating (i.e. restricting food consumption to a single fruit or meal) can be dangerous. This can indicate Anorexia Nervosa and/or Bulimia which are common eating disorders and can even be fatal.

How the body gets rid of fat

All body processes require energy to run properly. When the body is expending more energy than it is taking in (e.g. when exercising), the body's cells rely on internally stored energy sources, like complex carbohydrates and fats, for energy. The first source the body turns to is glycogen (by glycogenolysis). Glycogen is a complex carbohydrate (in total about 2000 kcal). 65% is stored in skeletal muscles and the rest in the liver. It is created from the excess of ingested macronutrients, mainly carbohydrates. When those sources are nearly depleted, the body begins lipolysis, the mobilization and catabolism of fat stores for energy. In this process, fats, obtained from adipose tissue, or fat cells, are broken down into glycerol and fatty acids, which can be used to make energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.

Fats are also secreted by the sebaceous glands (in the skin).

Psychological aspects of weight-loss dieting

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.

Cognitive Behavior Therapy has been effective in producing long term weight loss ^[6]. Judith S. Beck has been one of the most prominent practitioners and writers to bring this method to a popular audience.

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 that 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.

Weight loss groups

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.

Food diary

A July 2008 study, published in the American Journal of Preventive Medicine showed dieters who keep a daily food diary of what they eat lose twice as much weight as those who don't. The researchers concluded, "It seems that the simple act of writing down what you eat encourages people to consume fewer calories." ^[7]

Medications

Certain medications can be prescribed to assist in weight loss. Some, like amphetamines, are dangerous and are now banned for casual weight loss. Some supplements, including those containing vitamins and minerals, may not be effective for losing weight.

Diuretics

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.

Stimulants

Stimulants such as ephedrine or synephrine work to increase the basal metabolic rate and reduce appetite.

Dangers of fasting

Main article: Fasting

Lengthy fasting can be dangerous due to the risk of malnutrition and should be carried out under medical supervision. During fasting, low-carbohydrate or very low calorie diets lack blood glucose, the preferred energy source of the brain, causing the body to metabolize sugars from protein, which over a prolonged fast can lead to muscle wasting.

Side effects

Dieting, especially extreme food-intake reduction and rapid weight loss, can have the following side effects:

• Prolonged hunger
• Depression
• Reduced sex drive
• Fatigue
• Irritability
• Fainting
• Sinus problems (especially post-nasal drip)
• Muscle atrophy
• Rashes
• Acidosis
• Bloodshot eyes
• Gallbladder disease
• Seizures
• Malnutrition, possibly leading to death
• Subsequent weight gain

Low carbohydrate versus low fat

Main article: Medical research related to low-carbohydrate diets

Many studies have focused on diets that reduce calories via a low-carbohydrate (Atkins diet, Zone diet) diet versus a low-fat diet (LEARN diet, Ornish diet). The Nurses' Health Study, an observational cohort study, found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less coronary heart disease.^[8]

A meta-analysis of randomized controlled trials by the international Cochrane Collaboration in 2002 concluded^[9] that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people. A more recent meta-analysis that included randomized controlled trials published after the Cochrane review^[10][11][12] found that "low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered."^[13]

The Women's Health Initiative Randomized Controlled Dietary Modification Trial^[14] found that a diet of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily resulted in:

• no reduction in cardiovascular disease^[15]
• an insignificant reduction in invasive breast cancer^[16]
• no reductions in colorectal cancer^[17]

Additional recent randomized controlled trials have found that:

• A comparison of Atkins, Zone diet, Ornish diet, and LEARN diet in premenopausal women found the greatest benefit from the Atkins diet.^[18]

• The choice of diet for a specific person may be influenced by measuring the invididual's insulin secretion:

In young adults "Reducing glycemic [carbohydrate] load may be especially important to achieve weight loss among individuals with high insulin secretion."^[19] This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.^[20][21]

The American Diabetes Association released for the first time a recommendation (in its January 2008 Clinical Practice Recommendations) for a low carbohydrate diet to reduce weight for those with or at risk of Type 2 diabetes.^[22]

Low glycemic index

"The glycemic index factor is a ranking of foods based on their overall effect on blood sugar levels. Low glycaemic index foods, such as lentils, provide a slower more consistent source of glucose to the bloodstream, thereby stimulating less insulin release than high glycaemic index foods, such as white bread."^[23][24]

The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".^[25]

In a randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results^[26]:

• Diet 1 and 2 were high carbohydrate (55% of total energy intake)
  • Diet 1 was high-glycemic index
  • Diet 2 was low-glycemic index
• Diet 3 and 4 were high protein (25% of total energy intake)
  • Diet 3 was high-glycemic index
  • Diet 4 was low-glycemic index

Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3. Thus the authors concluded that the high-carbohydrate, low-glycemic index diet was the most favorable.

A meta-analysis by the Cochrane Collaboration concluded that low glycemic index or low glycemic load diets led to more weight loss and better lipid profiles. However, the Cochrane Collaboration grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index.^[23]

See also

References

External links

• Dieting at the Open Directory Project
• The food pyramid: Video lectures at the Harvard School of public health
• Comparing popular dieting plans: Video lecture at the Stanford University Medical Center
• A PBS Frontline interview with Prof. Walter Willett, Chair of Harvard's nutrition department