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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 dieting is used in combination with physical exercise to lose weight in those who are overweight or obese. Some athletes, however, follow a diet to gain weight (usually in the form of muscle). Diets can also be used to maintain a stable body weight.

Diets to promote weight loss are generally divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie.^[1] A meta-analysis of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2'4 kilogram weight loss in all studies.^[1] At two years, all calorie-reduced diet types cause equal weight loss irrespective of the macronutrients emphasized.^[2]

The first popular diet was "Banting", named after William Banting. In his 1863 pamphlet, Letter on Corpulence, Addressed to the Public, he outlined the details of a particular low-carbohydrate, low-calorie diet that had led to his own dramatic weight loss.^[3]

[edit] Types of diets

[edit] Low-fat diets

Low-fat diets involve the reduction of the percentage of fat in one's diet. Calorie consumption is reduced because less fat is consumed. Diets of this type include NCEP Step I and II. A meta-analysis of 16 trials of 2'12 months' duration found that low-fat diets (without intentional restriction of caloric intake) resulted in average weight loss of 3.2 kg (7.1 lb) over habitual eating.^[1]

[edit] Low-carbohydrate diets

Low carbohydrate diets such as Atkins and Protein Power are relatively high in fat and protein. They are very popular in the press but are not recommended by the American Heart Association. A review of 107 studies by Bravata et al. found that low-carbohydrate diets cause weight loss principally through calorie restriction obtained by not eating calories from carbohydrates.^[4] No adverse effects from low carbohydrate diets were detected.^[5]

Low-carbohydrate diets are often ketogenic (i.e. they restrict carbohydrate intake sufficiently to cause ketosis). No-carbohydrate diets are an extreme form of low-carbohydrate diets.

[edit] Low-calorie diets

Low-calorie diets usually produce an energy deficit of 500'1,000 calories per day, which can result in a 0.5 kilogram (1.1 lb) to 1 kilogram (2.2 lb) weight loss per week. Amongst some of the most commonly used low-calorie diets include DASH diet, Diet to Go, and Weight Watchers. The National Institutes of Health reviewed 34 randomized controlled trials to determine the effectiveness of low-calorie diets. They found that these diets lowered total body mass by 8% over 3'12 months.^[1]

[edit] Detox diets

Detox diets claim to eliminate bad toxins and poisons from the human body, increasing the amount of urin produced, thus not giving the body time enough to absorb fats and toxins contained in our everyday meals. Detox diets often have side effects, caused by the absence of these toxins, during the first two or three days, that may include, but are not limited to headaches, diarrea and feeling sleepy. A detox diet should never be embraced without first seeking medical advice on the subject.

[edit] Very low-calorie diets

Very low calorie diets provide 200'800 calories per day, maintaining protein intake but limiting calories from both fat and carbohydrates. They subject the body to starvation and produce an average weekly weight loss of 1.5'2.5 kilograms (3.3'5.5 lb). "2-4-6-8", a popular diet of this variety, follows a four-day cycle in which only 200 calories are consumed the first day, 400 the second day, 600 the third day, 800 the fourth day, and then the cycle repeats. These diets are not recommended for general use as they are associated with adverse side effects such as loss of lean muscle mass, increased risks of gout, and electrolyte imbalances. People attempting these diets must be monitored closely by a physician to prevent complications.^[1]

[edit] Fat loss versus muscle loss

Weight loss typically involves the loss of fat, water and muscle. Overweight people, or people suffering from obesity, typically aim to reduce the percentage of body fat. Additionally, as muscle tissue is denser than fat, fat loss results in increased loss of body volume compared with muscle loss. Reducing even 10% body fat can therefore have a dramatic effect on a person's body shape. To determine the proportion of weight loss that is due to decreased fat tissue, 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.^{[citation needed]}Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their 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."

Excessive protein intake, though not connected to declined kidney functioning in healthy individuals,^[6][7] may be harmful to those with certain kidney diseases.^[8] There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous, it has only been shown that these diets are dangerous in individuals already suffering from kidney and liver problems.

The Basal Metabolic Rate, which is the amount of calories the body expends at rest, meaning without performing any physical activity, is influenced by the person's total weight and total amount of muscle. The more muscle, the more calories a person can burn naturally. When the amount of muscle is increased, then more calories can be ingested without gaining weight. On the contrary, if the amount of fat is increased,increasing the number of calories ingested will only contribute to add weight.^[9]

Normally, when people lose weight, they lose a combination of fat and muscle. If the diet plan includes a daily caloric intake greater than the BMR, the person will most likely lose fat. On the contrary, if the person follows a diet that includes a lower caloric intake than the BMR, this person will lose fat but also a higher percentage of muscle. Severe diets may make people lose 50% fat and 50% muscle weight thus affecting their metabolism because by losing muscle the BMR gets affected. For instance, when a person goes on a low carb diet, the initial weight loss results from the glycogen depletion. Glycogen is a mixture of glucose and water mainly stored in the muscles. Therefore, much of the initial weight loss comes from muscle loss which affects the possibility to maintain a sustainable weight control. A study performed at the University of Connecticut also showed that athletes under a low carb diet not only experience a decrease in their performance but also a drop both in muscle power and cardiovascular performance.^[10]

Maintaining muscle mass while losing fat is therefore a key factor to reach both the ideal weight and body composition. To achieve this goal, experts advise not to reduce carbohydrates aggressively. Fat can be lost by reducing the calorie intake by 20% of daily needs for two days.^{[citation needed]} This reduced calorie intake, even in the presence of 100% carbohydrate consumption, allows for reduction of fat without muscle loss because the glycogen in the muscle is properly replenished.^[10]

Exercising on days when the highest amount of carbohydrates is consumed, 1.5 to 2 hours after eating, is also helpful to achieve a balanced fat reduction in the absence of muscle loss. Within this window of time, sugar and insulin levels are undergoing a slow decline. When insulin levels start dropping, the pancreas then produces the hormone glucagon while releasing nutrients stored in the fall cells to the blood to be turned into energy. On the contrary, if blood sugar levels suffer a high increase, insulin feeds the muscle cells and deposits excess into fat cells. Furthermore, if insulin levels decrease too much, the muscle cells do not receive the appropriate amount of food they require. There should always be a meal left during the day after exercising to allow the muscles to recover from exercise.^[10]

[edit] Energy obtained from food

The energy intake 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, while efficiency of utilization is affected by a variety of factors, including age, gender, body weight, hormone levels, and many more.

Chewing, especially in the elderly, has been shown to increase the intake of micronutrients. However, the effect of chewing on the intake of macronutrients, such as sugars, fats, and proteins has not been observed.^[11]

[edit] 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 construction, especially for the construction of muscle cells. 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 the 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 a satisfactory 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.^{[citation needed]} Retinol (oil-soluble vitamin A) is toxic in large doses. Vitamin E supplements have been found in some studies to increase mortality, congenital heart defects in offspring and an increased risk of stroke (see the corresponding article).^{[citation needed]} Most people can obtain their nutritional needs from their diet. In any event, a multivitamin taken once a day will suffice for the majority of the population.

Weight loss diets that manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have not been shown to be any more effective than diets that maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing).^[12] Extreme diets may, in some cases, lead to malnutrition.

Besides the importance of eating a balanced diet that includes all the necessary nutrients, other factors also contribute to healthy nutrition. Eating 5 or 6 small to medium sized meals throughout the day (instead of three big meals) has been shown to improve the metabolism.^{[citation needed]} As well, drinking sufficient amounts of water can help eliminate toxins and fat.^{[citation needed]} Processed, cooked, fried foods as well as sweets, junk foods, and alcohol should also be avoided in a healthy diet.^[13]

Nutritionists also agree on the importance of avoiding fats, especially saturated fats, to reduce weight and to be healthier. They also agree on the importance of reducing salt intake because commercial foods such as snacks, biscuits, and bread, among others, already contain salt, thus contributing to an excess of salt daily intake.^[14]

MyPyramid Food Guidance System is the result of extensive research performed by the United States Department of Agriculture to revise the original Food Guide Pyramid. It offers a wide array of personalized options to help individuals make healthy food choices. It also provides advice on physical activity.^[15]

[edit] How the body eliminates fat

All body processes require energy in order to function properly. When the body is expending more energy than it is consuming (e.g. when exercising), the body's cells rely on internally stored energy sources, such as complex carbohydrates and fats, for energy. The first source to which the body turns is glycogen (by glycogenolysis). Glycogen is a complex carbohydrate, 65% of which is stored in skeletal muscles and the remainder, in the liver (totaling about 2000 kcal in the whole body). 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 generate 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).

[edit] Psychological aspects of weight loss

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.^[16] 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.

The use of drugs to control appetite is also common. Stimulants are often taken as a means to suppress hunger in 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.

[edit] Weight loss groups

There exist both profit-oriented and non-profit weight loss organizations who assist people in their weight loss efforts. The former include Weight Watchers and Peertrainer. 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.^[17]

[edit] Food diary

A 2008 study published in the American Journal of Preventive Medicine showed that dieters who kept a daily food diary (or diet journal), lost twice as much weight as those who did not keep a food log, suggesting that the simple act of writing down what you eat encourages people to consume fewer calories.^[18] Accordingly, diet journal software and websites have gained significant popularity, and help people track calorie consumption, calorie burning, weight loss goals, and nutritional balance.

[edit] Medications

Certain medications can be prescribed to assist in weight loss. The most recent prescription weight loss medication released is Acomplia (generic name Rimonabant), manufactured by Sanofi Aventis. Used to treat obesity in persons with a BMI (body mass index) of 30 or above, as well as for smoking cessation treatments, Acomplia is still pending FDA approval for use in the United States. Other weight loss medications, 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 weight loss.

[edit] Diuretics

Diuretics induce weight loss through the excretion of water. Diuretics, which can be used in the forms of medications, supplements, or herbs, reduce overall body weight, but have no effect on an individual's total body fat content. Diuretics can thicken the blood, cause cramping, kidney and liver damage. In a single report, the death of Jacqueline Henson was found to be related to swelling in her brain, which was associated with excessive water consumption over a short period of time, while she was on a special water diet.^[19]

[edit] Stimulants

Stimulants such as ephedrine, green tea, caffeine or synephrine work to increase the basal metabolic rate.^{[citation needed]}

[edit] Dangers of fasting

Lengthy fasting can be dangerous due to the risk of malnutrition and should be carried out under medical supervision. During prolonged fasting or very low calorie diets, the reduction of blood glucose, the preferred energy source of the brain, causes the body to deplete its glycogen stores. Once glycogen is depleted the body begins to fuel the brain using ketones, while also metabolizing body protein (including but not limited to skeletal muscle) to be used to synthesize sugars for use as energy by the rest of the body. Most experts believe that a prolonged fast can lead to muscle wasting although some dispute this. The use of short-term fasting, or various forms of intermittent fasting have been used as a form of dieting to circumvent this issue.

[edit] Side effects

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

• 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
• Constipation, due to lack of food-intake
• Dehydration, due to lack of fluid-intake
• Lowered metabolism, if food intake is inadequate to the level of exercise, causing future attempts at weight loss to become more difficult
• Risk of developing Eating Disorders, especially Anorexia Nervosa or Bulimia Nervosa, even if initial intentions of dieting were health-wise
• Subsequent weight re-gain

[edit] Low carbohydrate versus low fat

Many studies have focused on diets that reduce calories via a low-carbohydrate (Atkins diet, Scarsdale 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.^[20] The same study also found no correlation (with multivariate adjustment) between animal fat intake and coronary heart disease (table 4).

A meta-analysis of randomized controlled trials by the international Cochrane Collaboration in 2002 concluded^[21] 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^[22][23][24] 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."^[25]

The Women's Health Initiative Randomized Controlled Dietary Modification Trial^[26] 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^[27]
• no statistically significant reduction in invasive breast cancer^[28]
• no reductions in colorectal cancer^[29]

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.^[30]

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

In young adults "Reducing glycemic [carbohydrate] load may be especially important to achieve weight loss among individuals with high insulin secretion."^[31] This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.^[32][33]

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.^[34]

[edit] Low glycemic index

"The glycemic index (GI) factor is a ranking of foods based on their overall effect on blood sugar levels. The diet based around this research is called the Low GI diet. Low glycemic index foods, such as lentils, provide a slower, more consistent source of glucose to the bloodstream, thereby stimulating less insulin release than high glycemic index foods, such as white bread."^[35][36]

The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".^[37]

In a randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results^[38]:

• 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.^[35]

[edit] See also

Body image Eating disorder Crash diet Dietitian Food Balance Wheel Food faddism Healthy diet

Wikiquote has a collection of quotations related to: Diet List of diets National Weight Control Registry Nutritional rating systems Nutrition scale Underweight Online weight loss plans

[edit] References

• Cheraskin, Emmanuel, M.D., D.M.D.. . 'The Breakfast/Lunch/Dinner Ritual', Journal of Orthomolecular Medicine Vol.8, No.1, 1993.
• Appleton, Nancy, Ph.D., 'Nibbling, Grazing and Frequent Meals'.

[edit] External links

• Dieting at the Open Directory Project
• The food pyramid: Video lectures at the Harvard School of public health
• US News and World Report, Health: Eat Like Our Ancestors. An Interview with Harvard Psychology's Deirdre Barrett 6/29/07.
• A PBS Frontline interview with Prof. Walter Willett, Chair of Harvard's nutrition department