Intentional weight loss refers to the loss of total body mass as a result of efforts to improve fitness and health, and/or to change appearance.
Weight loss in individuals who are overweight or obese can reduce health risks, increase fitness, and may delay the onset of diabetes. It could reduce pain and increase movement in people with osteoarthritis of the knee. Weight loss can lead to a reduction in hypertension (high blood pressure), however whether this reduces hypertension-related harm is unclear.
Weight loss occurs when an individual is in a state of negative thermodynamic flux: when the body is expending more energy (i.e. in work and metabolism) than it is consuming (i.e., from food or other nutritional supplements), it will use stored reserves from fat or muscle, gradually leading to weight loss.
It is not uncommon for some people who are at their ideal body weight to seek additional weight loss in order to improve athletic performance or meet required weight classification for participation in a sport. Others may be driven to lose weight to achieve a more attractive appearance. Being underweight is associated with health risks such as difficulty fighting off infection, osteoporosis, decreased muscle strength, trouble regulating body temperature and even increased risk of death.
According to the U.S. Food and Drug Administration (FDA), healthy individuals seeking to maintain their weight should consume 2,000 calories per day.
According to the Dietary Guidelines for Americans those who achieve and manage a healthy weight do so most successfully by being careful to consume just enough calories to meet their needs, and being physically active.
Low-calorie regimen diets are also referred to as balanced percentage diets. Due to their minimal detrimental effects, these types of diets are most commonly recommended by nutritionists. In addition to restricting calorie intake, a balanced diet also regulates macronutrient consumption. From the total number of allotted daily calories, it is recommended that 55% should come from carbohydrates, 15% from protein, and 30% from fats with no more than 10% of total fat coming from saturated forms. For instance, a recommended 1,200 calorie diet would supply about 660 calories from carbohydrates, 180 from protein, and 360 from fat. Some studies suggest that increased consumption of protein can help ease hunger pangs associated with reduced caloric intake by increasing the feeling of satiety. Calorie restriction in this way has many long-term benefits. After reaching the desired body weight, the calories consumed per day may be increased gradually, without exceeding 2,000 net (i.e. derived by subtracting calories burned by physical activity from calories consumed). Combined with increased physical activity, long-term low-calorie diets are thought to be most effective long term, unlike crash diets which can achieve short term results, at best. Physical activity could greatly enhance the efficiency of a diet. The healthiest weight loss regimen, therefore, is one that consists of a balanced diet and moderate physical activity.
Weight gain has been associated with excessive consumption of fats, sugars, carbohydrates in general, and alcohol. Depression, stress or boredom may also contribute to weight increase, and in these cases, individuals are advised to seek medical help. A 2010 study found that dieters who got a full night’s sleep lost more than twice as much fat as sleep-deprived dieters.
The majority of dieters regain weight over the long term.
There is some research that suggests that all calories are not created equal (in other words, a calorie is not necessarily a calorie). Thus the human body might not gain the same amount of weight from 500 calories of certain foods than it would from 500 calories of other foods.  
Therapeutic weight loss techniques
The least intrusive weight loss methods, and those most often recommended, are adjustments to eating patterns and increased physical activity, generally in the form of exercise. The World Health Organization recommended that people combine a reduction of processed foods high in saturated fats, sugar and salt and caloric content of the diet with an increase in physical activity.
An increase in fiber intake is also recommended for regulating bowel movements.
Other methods of weight loss include use of drugs and supplements that decrease appetite, block fat absorption, or reduce stomach volume.
Bariatric surgery may be indicated in cases of severe obesity. Two common bariatric surgical procedures are gastric bypass and gastric banding. Both can be effective at limiting the intake of food energy by reducing the size of the stomach, but as with any surgical procedure both come with their own risks that should be considered in consultation with a physician.
Dietary supplements, though widely used, are not considered a healthy option for weight loss. Even though a many are available, very few are effective long term.
Virtual gastric band uses hypnosis to make the brain think the stomach is smaller than it really is and hence lower the amount of food ingested. This brings as a consequence weight reduction. This method is complemented with psychological treatment for anxiety management and with hypnopedia. Research has been conducted into the use of hypnosis as a weight management alternative. In 1996 a study found that cognitive-behavioral therapy (CBT) was more effective for weight reduction if reinforced with hypnosis. Acceptance and Commitment Therapy ACT, a mindfulness approach to weight loss, has also in the last few years been demonstrating its usefulness.
A crash diet refers to willful nutritional restriction (except water) for more than 12 waking hours. The desired result is to have the body burn fat for energy with the goal of losing a significant amount of weight in a short time. Crash dieting can be dangerous to health and this method of weight loss is not recommended by physicians.
According to the Academy of Nutrition and Dietetics, “If the diet or product sounds too good to be true, it probably is. There are no foods or pills that magically burn fat. No super foods will alter your genetic code. No products will miraculously melt fat while you watch TV or sleep.” Certain ingredients in supplements and herbal products[vague] can be dangerous and even deadly for some people.
Weight loss industry
||The examples and perspective in this section deal primarily with USA and do not represent a worldwide view of the subject. Please improve this article or discuss the issue on the talk page. (December 2010)|
There is a substantial market for products which promise to make weight loss easier, quicker, cheaper, more reliable, or less painful. These include books, DVDs, CDs, cremes, lotions, pills, rings and earrings, body wraps, body belts and other materials, fitness centers, personal coaches, weight loss groups, and food products and supplements.
In 2008 between US$33 billion and $55 billion was spent annually in the US on weight-loss products and services, including medical procedures and pharmaceuticals, with weight-loss centers taking between 6 and 12 percent of total annual expenditure. Over $1.6 billion a year was spent on weight-loss supplements. About 70 percent of Americans’ dieting attempts are of a self-help nature. Although often short-lived, these diet fads are a positive trend for this sector as Americans ultimately turn to professionals to help them meet their weight loss goals.
In Western Europe, sales of weight-loss products, excluding prescription medications, topped £900 million ($1.4 billion) in 2009.