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 in those who are overweight or obese, 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.
Diets to promote weight loss are generally divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie. 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. At two years all diet types cause equal weight loss irrespective of the macronutrients emphasized.
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.
- Athletes participating in professional sports may sometimes undertake weight-gain diets to increase their body mass and gain advantage in their field.
- 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.
- Actors, and people participating in similar activities, may pursue weight loss or gain in order to better portray a particular role.
In children and young adults
Receiving adequate nutrition through a well-balanced diet is crucial during childhood and adolescence. Some diets can deprive the body of necessary nutrients, for instance lipids. In addition, there are some indications that the harmful effects of starvation or extreme dieting during adolescence exceed the expected benefits, sometimes even leading to increased weight gains.
Research shows that putting children on starvation or extreme diets 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 their life despite adequate nutritional intake.
Thermoregulation
As endotherms, humans expend energy to maintain our blood temperature at body temperature, which is approximately 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.
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.
Though the energy for muscle activity is primarily derived from the glycogen stored in the body, continued activity results in an increased use of the fatty acids as well. After the available glycogen stores are exhausted, fatty acids alone are used. It is often recommended that muscle activity be maintained for 20 minutes or more for increased usage of fatty acids.
The energy burnt during physical exercise has only a limited effect on weight loss, since an hour of aerobic exercise for a man in reasonable physical shape would burn about 2 megajoules (500 kilocalories), which is equivalent to only 60 grams (2 oz) of fat.
Both aerobic and anaerobic exercise would increase the basal metabolic rate (BMR) for some time after exercising. This leads to an additional caloric loss.
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. 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. 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.
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 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). Extreme diets may, in some cases, lead to malnutrition.
The impact of meal frequency
An important but often overlooked factor in weight gain or loss -- in addition to the kinds of foods that are ingested -- is meal frequency. A number of studies on the subject have determined that eating more frequent, smaller meals or “snacks” during the day tends to lower total serum cholesterol levels, improve glucose tolerance, and mute weight gain. Tests conducted on groups participating in this eating approach, often termed “grazing vs. gorging”, show that spreading caloric intake throughout the day instead of compressing it into two or three meals has positive effects on general health as well as on achieving and maintaining ideal weight.
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. 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. 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 (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." 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 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. There was even a report of a woman who died of swelling in her brain after she drank a large amount of water over a short period of time, while being on a special water diet.
Stimulants
Stimulants such as ephedrine or synephrine work to increase the basal metabolic rate and reduce appetite.
Dangers of fasting
Lengthy fasting can be dangerous due to the risk of malnutrition and should be carried out under medical supervision. During fasting or very low calorie diets the reduction of blood glucose, the preferred energy source of the brain, causes the body to metabolize sugars from protein. Most experts believe that a prolonged fast can lead to muscle wasting although some dispute this.
Side effects
Dieting, especially extreme food-intake reduction and rapid weight loss, can have the following side effects:
- Sinus problems (especially post-nasal drip)
- Gallbladder disease
- Malnutrition, possibly leading to death
- Subsequent weight gain
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.
A meta-analysis of randomized controlled trials by the international Cochrane Collaboration in 2002 concluded 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 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."
The Women's Health Initiative Randomized Controlled Dietary Modification Trial 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
- an insignificant reduction in invasive breast cancer
- no reductions in colorectal cancer
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.
- 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." This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.
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.
Low glycemic index
"The glycemic index factor is a ranking of foods based on their overall effect on blood sugar levels. 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 glycaemic index foods, such as white bread."
The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".
In a randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results:
- 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.
Calorie Counter
As people are searching more everyday online for dieting solutions there are now a vast array of online dieting tools and resources available. Sites such as Calorie Counter Pro and SparkPeople play an increasing role in offering assistance and help to those trying to achieve their weight loss goals.
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