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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 dieting is used in combination with physical exercise to lose weight in those who are overweight or obese. Some athletes however aspire 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]

Types of diets

Low-fat diets

Main article: Low-fat diet

Low-fat diets involve the reduction of the percentage of fat in one's diet. Calorie consumption is reduced but not purposely so. 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 resulted in weight loss of 3.2 kg (7.1 lb) over eating as normal.[1]

Low-carbohydrate diets

Main article: Low-carbohydrate diet

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 did not find that low-carbohydrate diets cause weight loss, except when calorie intake was restricted.[3] No adverse effects from low carbohydrate diets were detected.[4] Low carbohydrate diets do not support exercise very well[citation needed] , due to the fact that carbohydrates are the main source of energy during anaerobic exercise[citation needed] , such as sprinting or resistance training, and supply 30% or more during aerobic exercise[citation needed].

Low-calorie diets

Main article: Calorie restriction

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) weight loss per week. They include the DASH diet and Weight Watchers among others. 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]

Very low-calorie diets

Main article: Very low calorie diet

Very low calorie diets provide 200–800 kcal/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). 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]

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. 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 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, 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 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 individual factors, including body weight and hormones.

The effects of chewing, especially in elderly people, have been shown to affect the intake of micronutrients. However, there was no significant effect on the intake of macronutrients, such as sugars, fats, and proteins[6].

Proper nutrition

I notice that the mongoose gets lean on a diet of cockroaches. This would be invaluable to fat young ladies at home.

— David Livingstone, Open Letter

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 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. In any event, a multivitamin taken once a day will suffice for the majority of the population.

Weight-loss diets which manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have not been found to be more effective than diets which maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing).[7] Extreme diets may, in some cases, lead to malnutrition.

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, where 65% of it is stored in skeletal muscles and the rest 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 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 [8]. 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.

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 Peertrainer; 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.[9]

Food diary

A July 2008 study, published in the American Journal of Preventive Medicine, showed dieters who keep a daily food diary (or diet journal) of what they eat lose twice as much weight as those who do not. The researchers concluded, "It seems that the simple act of writing down what you eat encourages people to consume fewer calories."[10] Diet journaling software and websites have become popular to help people track calorie consumption, calorie burning, weight loss goals, and nutritional balance.

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 losing weight.

Diuretics

Diuretics induce weight loss through the excretion of water. These medications or herbs will reduce overall body weight, but will have no effect on an individual's body fat. 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.[11]

Stimulants

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

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 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 metabolize 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.

Side effects

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

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, 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.[12]

A meta-analysis of randomized controlled trials by the international Cochrane Collaboration in 2002 concluded[13] 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[14][15][16] 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."[17]

The Women's Health Initiative Randomized Controlled Dietary Modification Trial[18] 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[19]
  • an insignificant reduction in invasive breast cancer[20]
  • no reductions in colorectal cancer[21]

Additional recent randomized controlled trials have found that:

  • 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."[23] This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.[24][25]

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.[26]

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."[27][28]

The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".[29]

In a randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results[30]:

  • 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.[27]

See also

References

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  2. ^ "NEJM -- Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates".
  3. ^ Bravata DM, Sanders L, Huang J; et al. (2003). "Efficacy and safety of low-carbohydrate diets: A systematic review". JAMA. 289 (14): 1837–50. doi:10.1001/jama.289.14.1837. PMID 12684364. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
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  6. ^ Ildebrando appollonio, Corrado Carabellese, Alessandra Frattola, Marco Trabucchi: "Influence of dental status on dietary intake and survival in community-dwelling elderly subjects". Oxford University Press, 1997.
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  27. ^ a b Thomas D, Elliott E, Baur L (2007). "Low glycaemic index or low glycaemic load diets for overweight and obesity". 3: CD005105. doi:10.1002/14651858.CD005105.pub2. PMID 17636786. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link) Cite error: The named reference "pmid17636786" was defined multiple times with different content (see the help page).
  28. ^ Jenkins DJ, Wolever TM, Taylor RH; et al. (1981). "Glycemic index of foods: a physiological basis for carbohydrate exchange". Am. J. Clin. Nutr. 34 (3): 362–6. PMID 6259925. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
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  • American Dietetic Association. 2003. Position paper on vegetarian diets. J Am Diet Assoc. 103:748-765.
  • Curley, Sandra and Mark,The Natural Guide to Good Health. Lafayette, Louisiana. Supreme Publishing 1990
  • 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.)
  • Davis, B. and Melina, V. 2000. Becoming Vegan. pg. 22.
  • Wansink, B. Mindless Eating: Why We Eat More Than We Think, New York: Bantam Dell (2006).
  • 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”.
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