Weight loss in individuals who are overweight or obese can reduce health risks, increase fitness, and may delay the onset of diabetes. It can 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 is achieved by adopting a lifestyle in which fewer calories are consumed than are expended. Depression, stress, or boredom may 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. Though hypothesized that supplementation of vitamin D may help, studies do not support this. The majority of dieters regain weight over the long term. According to 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.

For weight loss to be permanent, changes in diet and lifestyle must be permanent as well. There is evidence that counseling or exercise alone do not result in weight loss, whereas dieting alone results in meaningful long-term weight loss, and a combination of dieting and exercise provides the best results. Meal replacements, and very-low-calorie diet interventions also produce meaningful weight loss.

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 recommends 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. Self-monitoring of diet, exercise, and weight are beneficial strategies for weight loss, particularly early in weight loss programs. Research indicates that those who log their foods about three times per day and about 20 times per month are more likely to achieve clinically significant weight loss.

An increase in fiber intake is 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.

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. A study found that cognitive-behavioral therapy was more effective for weight reduction if reinforced with hypnosis. Acceptance and commitment therapy, a mindfulness approach to weight loss, has been demonstrated as useful.