Overweight (Fat) is excess body weight, defined as a body mass index (BMI) of ≥ 25 kg/m2. Asians have a lower cut-off (≥ 23 kg/m2) for overweight. The waist circumference that increases risk of complications due to overweight are: Asian men: > 78 cm (> 30.7 in), Asian women: > 72 cm (> 28.3 in). General diagnosis is based on body mass index, and waist circumference.
Being fat leads to social, economic, physical appearance, self confidence, relationship, and health problems, as a result of prejudice, discrimination, poor body image, low self-esteem, under employment, and being unemployed. Health complications include but not limited to heart disease, vascular disease, stroke, diabetes mellitus, cancer, fatty liver, gallstones, liver scarring, joints problem, infertility, and psychologic disorders.
Treatment includes lifestyle modification (diet, nutrition, exercise, and behaviour), bariatric surgery, and medications.
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Heritability of high BMI is around 66%. Genetic factors may affect many of the signalling molecules and receptors used by parts of the hypothalamus and GI tract to regulate food intake (see Food Intake Regulation Pathway). Genetic factors can be inherited or result from conditions in utero (called genetic imprinting). Occasionally, obesity results from abnormal levels of peptides that regulate food intake such as Leptin or abnormalities in their receptors such as melanocortin-4 receptor.
Genetic factors also regulate energy expenditure, including basal metabolic rate, thermogenesis induced by diet, and non voluntary activity associated thermogenesis. Genetic factors may also have a greater effect on body fat distribution, especially abdominal fat (increases the risks of metabolic syndrome) than the amount of body fat.
Weight is gained when caloric intake exceeds energy needs. Determinants of energy intake include meal sizes, meal intake frequency, energy density of the meal. High caloric food such as oily food, meals high in refined carbohydrates, fruit juices, consumption of soft drinks, and alcohol can promote weight gain quickly. Diets high fiber such as fruits and vegetables, complex carbohydrates, lean proteins, and water as the main fluid consumed help minimize weight gain. A sedentary lifestyle promotes weight gain and metabolic syndrome.
Night eating syndrome consists of morning meal skipping, evening hunger, insomnia, followed by eating in the middle of the night. At least 35% to 50% of daily caloric intake occurs after evening meal. Similar but less extreme situations that contribute to excess weight gain include having late dinner prior sleep among the healthy general population.
Binge eating disorder is the consumption of large amounts of food quickly and without a sense of control during the binge and distress after it. Binge eating disorder may occur in about 10 to 30% of individuals entering weight loss programs.
Complications of being fat include diabetes mellitus, cardiovascular disorders, liver disease, gallbladder disease, gastroesophageal reflux, obstructive sleep apnea, infertility, low testosterone levels in men, erectile dysfunction, polycystic ovary syndrome in women, cancers (especially colon and breast cancer), osteoarthritis, joints problem, social, economic, and psychologic problems.