See also Atkins Diet
See also MyPyramid Diet

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 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.

Maintaining a healthy diet is the practice of making choices about what to eat with the intent of improving or maintaining good health. Usually this involves consuming necessary nutrients by eating the appropriate amounts from all of the food groups, including an adequate amount of water. Since human nutrition is complex, a healthy diet may vary widely, subject to an individual's genetic makeup, environment, and health (see below).

Types of dieting

There are several kinds of diets:

• Weight-loss diets restrict the intake of specific foods, or food in general, 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 from starvation, may undergo weight-gain diets which, unlike those of athletes, has the goal of restoring normal levels of body fat, muscle, and stores of essential nutrients.

Many people in the acting industry may choose to lose or gain weight depending on the role they're given.

As more cultures scrutinize their diets, many parents 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. A doctor should be consulted before putting any child on a specialized diet.

Research also 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]

In children and young adults

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).

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 <http://weightloss.about.com/cs/childhoodobesity/a/aa031804a.htm> 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.^[3]

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 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 calories) per day or 1 calorie 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 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 lb) man who wants to lose 10 kilograms (22 lb) and assume that he eats just enough to maintain his weight (at rest), so that weight loss can only come from exercise. Those 10 kilograms (22 lb) converted to work are equivalent to about 350 megajoules (84,000 calories). (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.

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. The exact figure is 14 calories 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.^[4] 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.

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.

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). 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

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, which is a complex carbohydrate stored in the liver, created from the excess which is ingested. When that source is 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). When losing weight one must be careful as to not begin to burn muscle. When the body runs of out of fats and carbohydrates to burn, it will begin to burn muscle which will be harmful for the body.

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.

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.

Dangers

Extreme calorie restriction, 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.

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 (now illegal in the United States due to an FDA ban) 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

See also

References

External links

• Dieting at the Open Directory Project
• Video lectures at the Harvard School of public health
• A PBS Frontline interview with Prof. Walter Willett, Chair of Harvard's nutrition department

Maintaining a healthy diet is the practice of making choices about what to eat with the intent of improving or maintaining good health. Usually this involves consuming necessary nutrients by eating the appropriate amounts from all of the food groups, including an adequate amount of water. Since human nutrition is complex, a healthy diet may vary widely, subject to an individual's genetic makeup, environment, and health. For around 20% of the planet's population, lack of food and malnutrition are the main impediments to healthy eating; people in developed countries have the opposite problem, and are more concerned about obesity.

Nutritional overview

Fresh Vegetables

Generally, a healthy diet is said to include:

1. Sufficient calories to maintain a person's metabolic and activity needs, but not so excessive as to result in fat storage greater than roughly 30% of body mass. 2,000 is the recommended daily allowance of calories for most people, but it depends on age, gender, height, and weight. (see Body fat percentage)
2. Sufficient quantities of fat, including monounsaturated fat, polyunsaturated fat and saturated fat, with a balance of omega-6 and long-chain omega-3 lipids. 65 grams is the recommended daily allowance of fat.
3. Maintenance of a good ratio between carbohydrates and lipids (4:1): four grams of the first for one gram of the second.
4. Avoidance of excessive saturated fat (although the "evidence" for this claim is forever in debate after the testimony of results provided by the Framingham Heart Study of 1948-1998)
5. Avoidance of trans fat.
6. Sufficient essential amino acids ("complete protein") to provide cellular replenishment and transport proteins. (All essential amino acids are present in animals. Some plants together give all the essential acids ex. rice and beans.)
7. Essential micronutrients such as vitamins and certain minerals.
8. Avoiding directly poisonous (e.g. heavy metals) and carcinogenic (e.g. benzene) substances;
9. Avoiding foods contaminated by human pathogens (e.g. e.coli, tapeworm eggs);
10. Avoiding chronic high doses of certain foods that are benign or beneficial in small or occasional doses, such as
    • foods or substances with directly toxic properties at high chronic doses (e.g. ethyl alcohol);
    • foods that may interfere at high doses with other body processes (e.g. refined table salt);
    • foods that may burden or exhaust normal functions (e.g. refined carbohydrates without adequate dietary fibre).

Governmental guidance

Although a healthy diet is based upon nutrition, people eat foods and not nutrients; as few people know which foods supply which nutrients, allowing people to self-regulate their diets means that they run the obvious risk of deficiency. Due to past difficulties of educating people about nutrient intake, governments have opted to counsel on what foods to eat rather than on what nutrients to ingest.

Most states set guidelines for a healthy diet -- these usually vary slightly from country to country based upon demographics. These guidelines do however usually share the same recommendations of eating less fried or fatty foods to reduce cholesterol. Many guidelines suggest replacing certain foods with healthier alternatives that supply an abundance of nutrients, for instance using legumes or beans within a salad or pasta.

As BMI and weight changes from person to person, the general Reference Nutrient Intakes (RNI) set by governmental institutions may be somewhat lacking for some people, despite the fact that the RNI is generally calculated as higher than the average nutrient intake. It is even thought^{[attribution needed]} that some people may have needs above that of the RNI, meaning even if a person ate the recommended amount of nutrients, they would still suffer deficiency. The only real way to know the RNI for many people is to monitor the intake of nutrients and amount of exercise.

Examples of specific recommendations include:

• The Dietary Reference Intake system, used to set recommended amounts of various nutrients on food labels in the United States and Canada.
• MyPyramid, formerly food guide pyramid, a graphical recommendation from the United States Department of Agriculture.
• Canada's Food Guide

Some groups have been critical of the U.S. pyramids, alleging poor scientific basis, and influence from food producers. Harvard School of Public Health researchers have proposed their own healthy eating pyramid.

A high-level summary of Government Guidance is:

• Make sure that you eat five different types of fruit and vegetables every day. Every day also make sure that you eat at least one thing from each of the different food groups: Carbohydrates, Fruit and vegetables, Protein, Dairy, and Fats. Remember to eat the most fruit and vegetables, and the least fats.

• Too much salt gives you high blood pressure; a high fat diet will give you hard and narrow arteries that could lead to heart attacks and strokes, possibly even death.

• Fruit and vegetables contain antioxidants which will keep you healthy as long as you team them up with regular daily exercise. Your efforts to eat healthily will go to waste if you do not take part in regular daily exercise.

• Having fibre in your diet will keep your digestive system going strong.

Detrimental eating habits

In specific individuals, ingesting foods containing natural allergens (e.g. peanuts, shellfood) or drug-induced triggers (e.g. tyramine for a person taking an MAO inhibitor) may be life-threatening.

Some foods have low nutritional value, and if consumed on a regular basis will contribute to the decline of human health. This has been demonstrated by various epidemiological studies that have determined that foods such as processed and fast foods are linked to diabetes and various heart problems.

When improperly cut or prepared, a small number of foods (such as fugu) can result in death.

The ingredient usually cited as being most crucial to good health, water, has even been known to result in death when consumed in extraordinary quantities.

Public policy issues

Fears of high cholesterol were frequently voiced up until the mid-1990s. However, more recent research has shown that the distinction between high- and low-density lipoprotein ('good' and 'bad' cholesterol, respectively) must be addressed when speaking of the potential ill effects of cholesterol. Low-density lipoprotein is often prevalent in animal products, such as bacon and egg yolks, whereas high-density lipoprotein is more common in plant and fish tissues, such as olive oil and salmon.

Media coverage of mass-produced, processed, "snack" or "sweet" products directly marketed at children has worked to undermine policy efforts to improve eating habits. The main problem with such advertisements for foods is that alcohol and fast food are portrayed as offering excitement, escape and instant gratification.

Particularly within the last five years government agencies have attempted to combat the amount and method of media coverage lavished upon "junk" foods. Governments also put pressure on businesses to promote healthy food options, consider limiting the availability of junk food in state-run schools, and tax foods that are high in fat. Most recently, the United Kingdom removed the rights for McDonald's to advertise its products as the majority of the foods that were seen to have low nutrient values were aimed at children under the guise of the "Happy Meal". The British Heart Foundation released its own government-funded advertisements, labeled "Food4Thought," which were targeted at children and adults displaying the gory nature of how fast food is generally constituted.

Food additive controversy

Some claim that food additives, such as artificial sweeteners, colorants, preserving agents, and flavorings may cause health problems. Examples of fast food critics include Kevin Trudeau and Eric Schlosser.

This short section requires expansion.

See also

Kinds of diets which may be prescribed for certain medical conditions

• Ketogenic diet, to reduce epileptic seizures
• Low-fat diet, to reduce heart disease and stroke
• Low-sodium diet, to reduce blood pressure and risk of stroke
• High-sodium diet, to reduce fainting spells in people with dysautonomia nerve conditions
• High-calorie diet, to combat cachexia due to AIDS, cancer, or drug side effects
• Low-oxalate diet, to combat kidney stones, vulvodynia, and possibly in combination with other diets, autism

Related articles

• Diet and cancer
• Diet and heart disease
• Diet (multiple sclerosis)
• Evolutionary nutrition
• Nutritional genomics
• Standard American Diet
• Red meat

References

1. ^  MAFF (Ministry of Agriculture, Fisheries and Food) 1990: Eight Guidelines for a healthy diet London: Food Sense
2. ^  Barasi, Mary E. (2003) Human Nutrition: A Health Perspective London:Arnold
3. ^  Mcdonalds Corporation Quality & Nutrition information - McDonalds USA Big-Mac Nutrition factsheet Mcdonalds Corporation (http://app.mcdonalds.com/bagamcmeal?process=item&itemID=5)
4. ^  Spurlock, M. Supersize Me - A film of epic Proportions Columbia Tristar
5. ^  Nestle, M. (1998) Animal v plant foods in human diets and health - Proceedings of the Nutrition Society
6. ^  National Health Service (2005) Five a day - a guide to healthy eating NHS Press (http://www.5aday.nhs.uk/)
7. ^  Johnson, R. K. (2000). The 2000 Dietary Guidelines for Americans: foundation of US nutrition policy. - British Nutrition Foundation Nutrition Bulletin 25. p241-248
8. ^  Achterberg, C., McDonnell, E., Fagby, R. (1994) How to put the Food Guide Pyramid into practice - Jornal of the American Dietetic Association Volume 94 p 1030-1035
9. ^  United Kingdom Department of Health (2005): Choosing Health: making healthier choices easier -- Public Health White Paper CM 6374 retrieved from: United Kingdom Department of Health Website
10. ^ United States Department of Agriculture (2005) . MyPyramid - Guidelines for healthy eating - Dietary guidelines for Americans USDA Press/Printing retrieved from United States Department of agriculture - MyPyramid replaces food pyramid guide
11. ^  Oliver, J., Channel Four (2005) Jamie's School Dinners - Documentary produced for channel four Television Programme.
12. ^  Food standards Authority (2005) 8 easy steps to keeping a healthy and balanced diet - Eat well, be well retrieved from Eat well, be well website.
13. ^  National Cancer Institute (2005) Eat five to Nine servings of fruits and vegetables per day retrieved from 5-a-day National Cancer institute
14. ^  British Heart Foundation (2005). Food4Thought - Campaign against junk food within children's diets. retrieved from British Heart Foundation Food4Thought