- Obesity facts
- What is obesity?
- How common is obesity?
- What are the health risks associated with obesity?
- What causes obesity?
- What are other factors associated with obesity?
- How is body fat measured?
- What about weight-for-height tables?
- What is the body mass index (BMI)?
- Does it matter where body fat is located? (Is it worse to be an "apple" or a "pear"?)
- What can be done about obesity?
- What is the role of physical activity and exercise in obesity?
- What is the role of diet in the treatment of obesity?
- Role of Medication
- What about herbal fen/phen?
- What about meal substitutes, artificial sweeteners, and over-the-counter (OTC) products?
- What is the role of surgery in the treatment of obesity?
- How can patients choose a safe and successful weight-loss program?
What causes obesity?
The balance between calorie intake and energy expenditure determines a person's weight. If a person eats more calories than he or she burns (metabolizes), the person gains weight (the body will store the excess energy as fat). If a person eats fewer calories than he or she metabolizes, he or she will lose weight. Therefore the most common causes of obesity are overeating and physical inactivity. Ultimately, body weight is the result of genetics, metabolism, environment, behavior, and culture.
- Genetics. A person is more likely to develop obesity if one or both parents are obese. Genetics also affect hormones involved in fat regulation. For example, one genetic cause of obesity is leptin deficiency. Leptin is a hormone produced in fat cells and also in the placenta. Leptin controls weight by signaling the brain to eat less when body fat stores are too high. If, for some reason, the body cannot produce enough leptin or leptin cannot signal the brain to eat less, this control is lost, and obesity occurs. The role of leptin replacement as a treatment for obesity is currently being explored.
- Overeating. Overeating leads to weight gain, especially if the diet is high in fat. Foods high in fat or sugar (for example, fast food, fried food, and sweets) have high energy density (foods that have a lot of calories in a small amount of food). Epidemiologic studies have shown that diets high in fat contribute to weight gain.
- A diet high in simple carbohydrates. The role of carbohydrates in weight gain is not clear. Carbohydrates increase blood glucose levels, which in turn stimulate insulin release by the pancreas, and insulin promotes the growth of fat tissue and can cause weight gain. Some scientists believe that simple carbohydrates (sugars, fructose, desserts, soft drinks, beer, wine, etc.) contribute to weight gain because they are more rapidly absorbed into the bloodstream than complex carbohydrates (pasta, brown rice, grains, vegetables, raw fruits, etc.) and thus cause a more pronounced insulin release after meals than complex carbohydrates. This higher insulin release, some scientists believe, contributes to weight gain.
- Frequency of eating. The relationship between frequency of eating (how often you eat) and weight is somewhat controversial. There are many reports of overweight people eating less often than people with normal weight. Scientists have observed that people who eat small meals four or five times daily, have lower cholesterol levels and lower and/or more stable blood sugar levels than people who eat less frequently (two or three large meals daily). One possible explanation is that small frequent meals produce stable insulin levels, whereas large meals cause large spikes of insulin after meals.
- Physical inactivity. Sedentary people burn fewer calories than people who are active. The National Health and Nutrition Examination Survey (NHANES) showed that physical inactivity was strongly correlated with weight gain in both sexes.
- Medications. Medications associated with weight gain include certain antidepressants (medications used in treating depression), anticonvulsants (medications used in controlling seizures such as carbamazepine [Tegretol, Tegretol XR , Equetro, Carbatrol] and valproate [Depacon, Depakene]), some diabetes medications (medications used in lowering blood sugar such as insulin, sulfonylureas, and thiazolidinediones), certain hormones such as oral contraceptives, and most corticosteroids such as prednisone. Weight gain may also be seen with some high blood pressure medications and antihistamines. The reason for the weight gain with the medications differs for each medication. If this is a concern for you, you should discuss your medications with your physician rather than discontinuing the medication, as this could have serious effects.
- Psychological factors. For some people, emotions influence eating habits. Many people eat excessively in response to emotions such as boredom, sadness, stress, or anger. While most overweight people have no more psychological disturbances than normal weight people, about 30% of the people who seek treatment for serious weight problems have difficulties with binge eating.
- Diseases such as hypothyroidism, insulin resistance, polycystic ovary syndrome, and Cushing's syndrome are also contributors to obesity.
- Social issues: A link between social issues and obesity has been established. Lack of money to purchase healthy foods or lack of safe places to walk or exercise can increase the risk of obesity.
National Institutes of Health (NIH); "Classification of Overweight and Obesity by BMI, Waist Circumference, and Associated Disease Risks." "Body Mass Index Table."
Manson JE, Colditz GA, Stampfer MJ, Willett WC, Rosner B, Monson RR, Speizer FE, Hennekens CH.; "A prospective study of obesity and risk of coronary heart disease in women." N Engl J Med. 1990 Mar 29;322(13):882-9.
W. B. Droyvold, T. I. Lund Nilsen, S. Lydersen, K. Midthjel, P. M. Nilsson, J. Nilsson, J. Holmen; "Weight change and mortality: the Nord-Trondelag Health Study." Journal of Internal Medicine. Volume 257 Issue 4, Pages 338 - 345
National Center for Health Statistics; "National Health and Nutrition Examination Survey." http://www.cdc.gov/nchs/nhanes.htm.
World Health Organization; "Global Database on Body Mass Index."
Life Measurements, Inc. (www.bodpod.com)
United States National Library of Medicine, National Institutes of Health; "Bioelectric Impedance Analysis in Body Composition Measurement."
Lars Sjöström, M.D., Ph.D., Anna-Karin Lindroos, Ph.D., Markku Peltonen, Ph.D., Jarl Torgerson, M.D., Ph.D., Claude Bouchard, Ph.D., Björn Carlsson, M.D., Ph.D., Sven Dahlgren, M.D., Ph.D., Bo Larsson, M.D., Ph.D., Kristina Narbro, Ph.D., Carl David Sjöström, M.D., Ph.D., Marianne Sullivan, Ph.D., Hans Wedel, Ph.D.. "Lifestyle, Diabetes, and Cardiovascular Risk Factors 10 Years after Bariatric Surgery." New England Journal of Medicine. Volume 351:2683-2693, December 23, 2004.
U.S. Department of Health and Human Services, U.S. Department of Agriculture; "Dietary Guidelines for Americans."