Obesity, sometimes also called being excessively overweight, is an abnormal accumulation of body fat, usually 20% or more over an individual's ideal body weight. A person is considered overweight if his or her body mass index (BMI) is between 25 and 29.9, and a person is considered obese if the BMI is over 30. Obesity can severely interfere with one's daily functions, and it is associated with increased risk of illness, disability, and even death.
Obesity levels have tripled worldwide since 1975. In 1980, rates began a sudden upward trend and have climbed since then. As of 2018, more than 13% of the world's adult population, and 38% of the United States' adult population, was obese.
The branch of medicine that deals with the study and treatment of obesity is known as bariatrics. As obesity has become a major health problem in the United States, bariatrics has become a separate medical and surgical specialty.
Obesity is a serious public health problem that affects both sexes and all ethnic, racial, age, and socioeconomic groups in the United States and around the world. According to the U.S. Centers for Disease Control and Prevention (CDC), in 2013–2014 about 38% of adults (35% of adult men and 40% of adult women) in the United States were obese. Another 33% were overweight. Nearly eight percent of adults were extremely obese, with 17.2 % of children ages 2 to 19 being obese. The percentage of obese children increases with age, so that adolescents actually had an obesity rate of 20.6%. All of these numbers had increased from levels recorded in 2010, which were already quite high. They were an extreme difference from obesity levels in the late 1970s, when about 12% of men and 15% of women were obese. Rates of obesity began an abrupt upward climb in about 1980; interestingly, the numbers of overweight individuals have remained roughly stable over that entire period whereas those for obesity have soared.
The prevalence of obesity varies with age and ethnicity. According to the CDC, non-Hispanic blacks have the highest rate of obesity in the United States, with a rate of 48.4%, followed by Hispanics (42.6%), and non-Hispanic whites (36.4%). The greatest rates of obesity were found in the South and Midwest. With respect to socioeconomic status, non-Hispanic black men and Mexican American men with higher incomes were more likely to be obese than those with lower incomes. With respect to females, all women with higher incomes were less likely to be obese than lower-income women. Education backgrounds did not seem to affect obesity levels. Among children, African American and Hispanic children were considerably more likely to be overweight than Caucasian Americans.
Obesity is a problem around the world. Eurostat announced in 2016 that one in six of European Union residents were obese; 35.7% of adults were overweight, and 15.9% were obese.
The World Health Organization (WHO) recognizes obesity as a global problem. WHO estimated in 2011 that 1.5 billion people worldwide were overweight, of which 500 million were obese. By 2016 those numbers had climbed to 1.9 billion overweight adults and 650 million obese adults. In 2016, over 340 million children were overweight or obese. The number of overweight children in Africa and Asia is increasing most rapidly, whereas in the same countries, other children are dying of complications of malnutrition or starvation.
Obesity is excessive body weight that develops over time as people store more energy than they expend.
Percentage of overweight, obese, and extremely obese adults in the United States, 2016
Age 20 ≥ yrs.
Overweight (BMI 25 to 29.9)
Obese (BMI 30 to 39.9)
Extremely obese (BMI 40 and above)
SOURCE: Centers for Disease Control. “Defining Adult Overweight and Obesity.” https://www.cdc.gov/obesity/adult/defining.html (accessed April 11, 2018).
The human body is composed of bone, muscle, specialized organ tissues, and fat. Together these comprise the total body mass, measured in pounds (lb) or kilograms (kg). Fat is an energy source for the normal physiologic function of cells and organs and is an important building block for all cells of the body. Fat, or adipose tissue, is also stored as a reserve supply of energy. It accumulates in the chest and abdomen and, in much greater volume, under the skin but is also found around the internal organs. When the amount of energy consumed as food exceeds the amount of energy expended in the maintenance of life processes and physical activity, storage fat accumulates in excessive amounts.
Current guidelines use the body mass index (BMI) to define obesity. The BMI utilizes height and weight to compare the ratio of body fat to total body mass. To calculate BMI using metric units, weight in kilograms is divided by height in meters squared. To calculate BMI in English units, weight in pounds is divided by height in inches squared and then multiplied by 703. This calculated BMI is compared to the statistical distribution of BMIs for adults aged 20–29 to determine whether an individual is underweight, average, overweight, or obese. The 20–29-year age group was chosen as the standard because it represents fully developed adults at the point in their lives when they have the least amount of body fat. Ideally, body fat is about 15% of total body mass for adult males and about 20%–25% for adult females. BMI does not distinguish between fat and muscle, so some very muscular individuals have high BMIs, but for most purposes BMI works adequately.
Adult BMIs are age- and gender-independent. All adults aged 20 and older are evaluated on the same BMI scale as follows:
Ranges are slightly different for Asian populations. Research has shown that the risk of developing type 2 diabetes and heart disease tends to be associated with lower BMIs in Asian populations than in European populations (on which the BMIs are based). Ranges vary, but generally the cap for normal weight is set at 22.9, and a BMI of 23 or higher is considered overweight.
Waist measurement alone can also be a valuable metric for obesity screening, particularly because fat distribution patterns affect health risks. Large amounts of abdominal fat increase a person's risk for heart disease and type 2 diabetes. Risks increase at a waist measurement of 35 inches (89 cm) for women and 40 inches (102 cm) for men.
The BMI for children and teens is calculated in the same way as for adults, but the results are interpreted differently. A child's BMI is compared to those of other children of the same age and gender and assigned to a percentile. For example, a girl in the 75th percentile for her age group weighs more than 74 of every 100 girls her age and less than 25 of every 100 girls her age. The percentiles indicate the following:
Obesity places stress on the body's organs and puts people at higher risk for many serious and potentially life-threatening health problems:
Obese individuals have a shorter life expectancy than people of normal weight. Many diseases, especially degenerative diseases of the joints, heart, and blood vessels, tend to be more severe in obese individuals, increasing the need for some surgical procedures. Liver and renal disease and diseases such as Alzheimer's are also more common in obese individuals. Simply performing surgery on an obese person is difficult and dangerous. Childhood obesity increases the risk of deformed bones in the legs and feet. It can also result in emotional disorders, such as depression caused by social isolation and negative comments by peers. Moreover, childhood obesity increases the risk of high blood pressure and type 2 diabetes in early life, and all risks of obesity, including cardiovascular disease, will be increased it if persists into adulthood.
Obesity and type 2 diabetes are strongly associated with one another. Obesity is believed to account for 80%–85% of the risk of developing type 2 diabetes, and recent research suggests that obese people are up to 80 times more likely to develop type 2 diabetes than those with a BMI of less than 22. Abdominal fat causes fat cells to release “pro-inflammatory” chemicals, which can make the body less sensitive to the insulin (insulin resistant) it produces by disrupting the function of insulin responsive cells and their ability to respond to insulin. Recent research exploring the causation has also suggested that high insulin levels may actually cause obesity, providing a new view on the link between these conditions. Metabolic syndrome is a cluster of symptoms that include abdominal obesity, high blood sugar, high blood pressure, high triglycerides, and low HDL cholesterol; an individual with at least three of these is considered to have metabolic syndrome. High blood sugar tends to go along with high levels of insulin and insulin resistance, a condition in which the body's cells do not respond readily to insulin and thus the pancreas produces more of it. Metabolic syndrome greatly increases an individual's risk of developing type 2 diabetes. As of 2015, more than 30 million adult Americans (over nine percent of the population) were thought to have diabetes; about 7 million of these were believed to be undiagnosed. The vast majority of these had type 2 diabetes. Worldwide, the prevalence of diabetes among adults increased from 4.7 percent of the population in 1980 to 8.5 percent (422 million people) in 2014.
In 2017, the healthcare cost of obesity to the American economy was estimated at nearly $200 billion, almost 21% of annual medical spending. This does not even include dollars spent on commercial weight-loss programs. Diabetes was the seventh leading cause of death in the United States in 2015. The increasing prevalence of obesity and diabetes in children and young adults heralds increased healthcare costs in the future. The social costs of obesity, including decreased productivity, discrimination, depression, and low self-esteem, are less easily measured.
Obesity tends to run in families. Children of obese parents are about 13 times more likely than other children to be obese. Having additional obese family members, including siblings and grandparents, greatly increases the likelihood of childhood obesity. The tendency toward a body type with an unusually high number of fat cells, termed endomorphic, appears to be inherited. Other genetic factors influence appetite and the metabolic rate at which food is transformed into energy. Family eating habits also are major contributors to the development of obesity. Although the majority of adopted children have patterns of weight gain that more closely resemble those of their birth parents than those of their adoptive parents, normal-weight children adopted into obese families are more likely than other children to become obese. Longitudinal studies of juvenile-onset obesity have demonstrated parental and peer encouragement of overeating and even deliberate overfeeding of obese children.
During past decades, worldwide eating habits have changed significantly. People are consuming larger meals and more high-calorie processed foods than they did in the past. Food and sugary beverages are sold nearly everywhere, in larger sizes than were typical in the past. School and workplace cafeterias often have a poor selection of nutritional food offerings. Many people eat frequently.
The question of what exactly causes obesity, though, is a matter of considerable disagreement among experts worldwide. People are certainly consuming more calories than they used to. But the exact mechanisms that are producing the obesity epidemic are more complicated than that, and experts have suggested a number of theories to account for this rapid increase.
The traditional explanation for obesity has been that obesity is caused by the consumption of more calories than the body uses for energy to drive physiological functions. The excess calories are stored as adipose tissue. Obesity is the direct result of overeating; the composition of diet is not as important as total energy content because a calorie is a calorie. Recommendations for low-fat diets are based partly on the fact that fat contains more calories per gram than either protein or carbohydrates, so reducing fat should reduce overall calorie consumption. To lose weight, a person must reduce calories to the point that the person is burning more calories than he or she is consuming. Reduced-calorie diets have been proven effective at producing immediate and steady weight loss, though many people regain weight after they stop dieting.
Obesity tends to occur within communities. Eating habits, physical activity, time spent in sedentary activities (e.g, sitting and not moving, watching TV, etc.) and environmental, behavioral, social, and cultural factors all contribute to the development of obesity.
Maternal factors are significant. The children of a woman who is obese during pregnancy are likely to be obese themselves and to have a high risk of later developing coronary heart disease, stroke, type 2 diabetes, and asthma. Maternal obesity can also lead to poorer cognitive performance and increased risk of neurodevelopmental disorders, including cerebral palsy. Research published in The Lancet in 2016 found that maternal obesity was a significant factor in health problems during childhood and later adult life, and warned of serious public health implications related to current obesity levels that may spread into the future, as obese women produce children.
Some environmental factors may be at work as well. Endocrine-disrupting chemicals such as estrogens can cause weight gain; estrogens are found in pesticides, birth control pills, soy products, and even plastics used in water bottles (BPA), and are ubiquitous in water supplies. Phtalates in plastics, organochloride pesticides, and air pollution have also been proposed as possible contributors to obesity. Antibiotics, given to both humans and animals, have been associated with weight gain.
Recent research has questioned the energy balance explanation and proposed that instead obesity is a hormonal disorder caused by excess insulin, the hormone that causes the body to store glucose as fat. According to Dr. Jason Fung, high insulin levels cause weight gain. People get fat because their insulin levels are too high. Calorie consumption has little to do with it. By this thinking, obesity does not cause diabetes; hyperinsulimia and diabetes cause obesity. A growing body of peer-reviewed scientific studies published in the late 2010s support this view, finding evidence that reducing dietary carbohydrates is effective at improving glycemic control and insulin response, and producing weight loss. Pediatric endocrinologist Robert Lustig points out that blaming obesity on overeating effectively blames the victim for choosing bad habits; no one wants to be obese, and obese children certainly have not chosen to overeat.
Many experts now attribute the obesity epidemic to a modern diet that is high in carbohydrates, especially in sugar. Gary Taubes in The Case Against Sugar argues that rates of high insulin and type 2 diabetes began to appear in the late 19th century, when sugar became readily available for the first time in human history. Sugar and carbohydrates raise blood sugar and cause the pancreas to secrete insulin. Fructose and high-fructose corn syrup are particularly problematic in the United States. The proportion of carbohydrates in the diet grew in the late 20th century, as people changed their diets to reduce overall fat consumption, resulting in a dietary pattern that is different from historical norms that included larger amounts of fat (with of course the caveat that diets vary widely). The pancreas secretes more and more insulin as the body's cells become resistant to its effects. These high levels of insulin force the body to store more and more fat, and prevent it from releasing fat stores to be used as energy. Because insulin is secreted every time a person eats, no matter what they eat, eating every two or three hours— often recommended as a weight-loss method because it would keep blood sugar levels constant—only adds to the consistently high levels of insulin in the body. Fung, by contrast, recommends long periods of fasting (12 hours or longer every day) to allow insulin levels to drop long enough for people to burn their own fat stores for fuel.
Dr. Timothy Noakes attributes current rates of diabetes and obesity to the low-fat dietary guidelines that were adopted in the United States in 1978, a trend quickly followed by other nations. Worldwide obesity rates started their rapid upward climb in 1980. During the 1980s and 1990s people were encouraged to drastically reduce their consumption of fat, especially saturated fat. As Nina Teicholz describes in The Big Fat Surprise, they did; consumption of butter, red meat, and full-fat dairy dropped rapidly as people tried to follow a healthy diet. As obesity rates climbed, people were encouraged to cut calories; obesity was attributed to overeating.
Fung, Noakes, and many others claim that the low-fat low-calorie recommendations were a failure; obesity and diabetes rates have skyrocketed, directly as a result of people reducing fat and increasing carbohydrates. Many researchers have observed that people who transition rapidly from a traditional diet to a modern processed one will display a rapid rise in high blood sugar, diabetes, and obesity; Taubes, Fung, and other supporters of a low-carbohydrate diet point to this as proof that composition of the diet is key.
Nevertheless, sometimes obesity does have a purely physiological cause, as in the following:
Some researchers have suggested that low levels of the neurotransmitter serotonin increase cravings for carbohydrates. In addition, a combination of genetics and early nutritional habits may result in a higher “set point” for body weight that causes obese individuals to feel hunger more often than others. Recent obesity research has focused on two peptide hormones, leptin and ghrelin. Leptin, produced by fat cells, affects hunger and eating behavior; insensitivity to leptin may contribute to obesity. Ghrelin is secreted by cells in the lining of the stomach and is important in appetite regulation and maintaining the body's energy balance.
Sedentary lifestyles are often said to contribute to obesity. Rather than performing physical labor on farms and in factories, many people are now employed at sedentary jobs in post-industrial service industries. Energy-saving machines and devices—cars, remote control devices, household electric appliances, and power tools—have become standard equipment, and people do not walk for transportation nearly as much as they did before automobiles became widespread. Conversely, researchers have pointed out that obesity can occur even in people who are in fact physically quite active; the Hopi Indians, for example, experienced rapid increases in obesity in the mid-20th century even while they were walking long distances every day and engaging in strenuous physical labor such as factory work or cleaning.
Psychological factors, such as depression and low self-esteem, can contribute to overeating and obesity. People may eat compulsively to overcome fear or social maladjustment, express defiance, or avoid intimate relationships.
Obese mothers are more likely to give birth to larger babies. This can be caused by excessive insulin production in the fetuses of diabetic mothers, excessive trans-placental nutrients in the case of obese mothers, or excessive weight gain during pregnancy. Some babies become overweight because they are overfed. Families may value a plump baby, or caregivers may use a bottle to quiet an infant or to demonstrate their own competence as caregivers. Feeding infants and toddlers sugary foods and drinks can make them gain weight rapidly.
The major symptoms of obesity are excessive weight and large amounts of fatty tissue. Common secondary symptoms include shortness of breath and lower back pain from carrying excessive body weight. Obesity can also give rise to secondary conditions including:
Obesity is usually diagnosed by observation of excessive storage fat and by calculating BMI from weight and height. Physicians also observe how the excess weight is carried by comparing waist and hip measurements: “apple-shaped” patients, who store most of their weight around the waist and abdomen, are at greater risk for cancer, heart disease, stroke, and diabetes than “pear-shaped” patients, whose extra pounds settle primarily in their hips and thighs.
BMIs and other measurements do not necessarily accurately reflect body composition and muscle mass. A heavily muscled football player may weigh far more than a sedentary man of similar height but have significantly less body fat. Chronic dieters, who have lost significant muscle mass during periods of caloric deprivation, may look slim and weigh little but have elevated body fat. Therefore direct measurements of body fat are obtained using calipers to measure skinfold thickness at the back of the upper arm and other sites, which distinguishes between muscle and adipose tissue.
The most accurate means of estimating body fat is hydrostatic weighing, calculating the volume of water displaced by the body. The patient exhales as completely as possible and is immersed in water, and the relative displacement is measured. Women whose body fat exceeds 30%–32% of total body mass by this method and men whose body fat exceeds 25%–27%, are generally considered obese. Because this method is unpleasant and impractical, it is usually used only in scientific studies.
Treatment of obesity aims at reducing weight to a BMI within the normal range (below 25.0) with dietary modifications. This has proven to be quite difficult. Obese people regularly lose weight on diets and then regain it when they resume their previous practices. “Yo-yo” dieting, in which weight is repeatedly lost and regained, has been shown to increase the likelihood of fatal health problems even more than no weight loss at all.
For morbidly obese individuals, dietary changes and behavior modification may be accompanied by bariatric surgery. Gastroplasty involves inserting staples to decrease the size of the stomach. Gastric banding is an inflatable band inserted around the upper stomach to create a small pouch and narrow passage into the remainder of the stomach. Bariatric surgery has become less risky in recent years due to innovations in equipment and surgical techniques. Nevertheless, it is only performed on patients for whom supervised diet and exercise strategies have failed, who are at least 100 lb. (45 kg) overweight or twice their ideal body weight, and whose obesity seriously threatens their health. Risks and possible complications include infections, hernias, and blood clots. Overall, 10%–20% of patients who undergo weight-loss surgery require additional operations to correct complications, more than 33% develop gallstones, and 30% develop nutritional deficiencies, such as anemia, osteoporosis, or metabolic bone disease.
Other bariatric surgical procedures—including liposuction, a purely cosmetic procedure in which a suction device removes fat from beneath the skin, and jaw wiring, which can damage gums and teeth and cause painful muscle spasms—have no place in obesity treatment.
Weight loss is recommended for obese children over age seven and for obese children over age two who have medical complications. Weight maintenance is an appropriate goal for children over the age of two who have no medical complications. Most treatment approaches to childhood obesity involve a combination of caloric restriction, physical exercise, and behavioral therapy. Bariatric surgery is considered as a last resort only for adolescents who are fully grown.
The short-term use of prescription medications may assist some individuals in managing their condition, but it is never the sole treatment for obesity, nor are drugs ever considered as a cure for obesity. Diet drugs are designed to help medically at-risk obese patients “jump-start” their weight-loss effort and lose 10% or more of their starting body weight, in combination with a diet and exercise regimen. Prescription weight-loss drugs are approved by the U.S. Food and Drug Administration (FDA) only for patients with a BMI of 30 or above, or a BMI of 27 or above and an obesity-related condition, such as high blood pressure, type 2 diabetes, or dyslipidemia (abnormal amounts of fats in the blood). The weight is usually regained as soon as the drugs are discontinued, unless eating and exercise habits have changed.
Most appetite-suppressants are based on amphetamine. They increase levels of serotonin or catecholamine, brain chemicals that control feelings of fullness. Serotonin also regulates mood and may be linked to mood-related eating behaviors. Prescription weightloss medications include:
Although most of the immediate side effects of appetite suppressants are harmless, their long-term effects may be unknown. Dexfenfluramine hydrochloride (Redux), fenfluramine (Pondimin), and the fenfluramine-phentermine combination (Fen-Phen) were taken off the market after they were shown to cause potentially fatal cardiac effects. Sibutramine (Meridia) was known to significantly elevate blood pressure and was taken off the market in 2010. Phenylpropanolamine, a component of many nonprescription weight-loss and cold and cough medications (Acutrim, Dex-A-Diet, Dexatrim, Phenldrine, Phenoxine, PPA, Propagest, Rhindecon, Unitrol) was removed from shelves because of an increased risk of stroke. Appetite suppressants can be habit-forming and have the potential for abuse. Appetite suppressants should not be used by patients taking monoamine oxidase inhibitors (MAOIs) and are not recommended for children.
Side effects of prescription and over-the-counter weight-loss products may include:
Unlike appetite suppressants, orlistat is a lipase inhibitor that reduces the breakdown and absorption of dietary fat in the intestines. Both its prescription (Xenical) and nonprescription (Alli) forms are approved by the FDA. Orlistat is intended to be used with a calorie-controlled diet and exercise program. Side effects may include abdominal cramping, gas, fecal urgency, oily stools, frequent bowel movements, and diarrhea.
Other drugs are sometimes prescribed off-label for treating obesity. For example, fluoxetine (Prozac) is an antidepressant that sometimes aids in temporary weight loss. Side effects of this medication include diarrhea, fatigue, insomnia, nausea, and thirst.
In the 2010s, a number of medical professionals began advocating a low-carbohydrate high-fat diet as a treatment for obesity and diabetes. They reported success at treating patients suffering from high insulin levels, high blood sugar, high blood pressure, obesity, diabetes, and related problems.
Low carbohydrate diets are not new. William Banting published a version of a low-carb diet in 1863; in South Africa, low-carb diets are still known as Banting diets. Dr. Eliot Joslin used low-carb diets to treat diabetics in the first decades of the 20th century. Cardiologist William Atkins popularized low-carb dieting starting in the 1970s, and the Atkins diet has enjoyed intermittent popularity since then.
Supporters of low-carb diets, which are also high in fat and low to moderate in protein, claim that they address the insulin issues at the root of obesity. Eating carbohydrates causes the body to release insulin, but eating fat does not. By drastically reducing carbohydrates, a low-carb diet keeps insulin levels low enough to allow the body to access its own fat stores.
Intermittent fasting further reduces the amount of insulin in the body. Insulin is released every time a person eats, even if the food is low-carb. Fasting allows insulin levels to drop and stay down. The fasting person then burns his or her own fat stores for energy. Though many people fast for 12 to 18 hours every day, multi-day fasts are possible. In one study, obese patients who participated in multi-day fasts found that their insulin levels dropped rapidly and they readily lost weight.
The online Virta clinic uses low-carb diets to reverse type 2 diabetes. Virta treats patients with continuous remote monitoring and coaching in a ketogenic diet. Patients who follow a very low-carb diet can maintain blood glucose values below the range defined as diabetic. Weight loss typically accompanies this. The Virta Clinic's website maintains a list of recently published scientific papers supporting their approach, including the clinic's own research published in 2018 which found that type 2 diabetes could be reversed with a ketogenic diet. Patients in the study significantly reduced their use of insulin, 60% reversed their type 2 diabetes and achieved an average weight loss of 30 pounds over one year.
Low-carbohydrate diets, like other diets that produce weight loss, only work as long as a person follows them. To cure obesity, a person must make permanent lifestyle changes. High blood sugar and weight gain will reappear if a person resumes his or her old dietary habits.
Functional food diets are a newer, as yet unproven, approach to weight loss. They include:
Various herbs and supplements are promoted for weight loss, although there is insufficient evidence that these are effective in encouraging long term weight loss:
Acupressure and acupuncture can suppress food cravings. Visualization and meditation can create and reinforce a positive self-image that can enhance a patient's determination to lose weight. By improving physical strength, mental concentration, and emotional serenity, yoga can provide the same benefits. Patients who play soft slow music during meals often find that they eat less food, but enjoy it more. Physical activity can suppress appetite by releasing the hormone ghrelin.
Support and self-help groups such as Overeaters Anonymous and TOPS (Taking Off Pounds Sensibly) that promote nutritious, balanced diets can help patients maintain proper eating regimens. Many diet support groups also exist on the Internet.
Weight should be lost gradually and steadily by decreasing calories while maintaining an adequate nutrient intake. A daily caloric intake of 1,000–1,200 calories for women and 1,200–1,600 for men enables most people to lose weight safely. A loss of about 2 lb. (1 kg) per week is recommended. Diets of less than 800 calories a day should never be attempted unless prescribed and monitored by a physician.
At least 60–90 minutes of daily moderate-intensity physical activity is usually recommended for health reasons, but attention to diet is necessary to maintain weight loss. Obese people who have led sedentary lives may need monitoring to avoid injury as they begin to increase their physical activity. Exercise should be increased gradually, perhaps starting by climbing stairs instead of taking elevators, followed by walking, biking, or swimming at a slow pace. Eventually 15 minute walks can be built up to brisk 45–60-minute walks.
The American Academy of Family Physicians offers advice for families with children who need to maintain or lose weight:
The primary factor in achieving and maintaining weight loss is a life-long commitment to healthy eating habits. As many as 85% of dieters who do not exercise on a regular basis regain their lost weight within two years, and 90% regain it within five years. Short-term diet programs and repeatedly losing and regaining weight encourage the storage of fat and may increase the risk of heart disease.
The chronically or habitually obese tend to come from families with a larger number of risk factors for obesity and have a much more difficult time losing weight than the newly obese. Likewise, previously obese people have a high probability of reverting to obesity.
When obesity develops in childhood, the total number of fat cells increases (hyperplastic obesity), whereas in adulthood the total amount of fat in each cell increases (hypertrophic obesity). Patients who were obese as children may have up to five times as many fat cells as a patient who became obese as an adult. Decreasing the amount of energy (food) consumed or increasing the amount of energy expended reduces the amount of fat in the cells but does not reduce the number of fat cells already present, and this process is slow, just like the accumulation of excess fat.
Neonatal obesity does not necessarily translate into childhood or adult obesity, but the probability for weight problems increases if the child is born or adopted into a family with multiple obese members. Likewise, excess weight in a child under the age of three does not necessarily predict adult obesity unless one of the parents is obese.
According to the Obesity Prevention Center at the University of Minnesota, obesity-control programs that rely on educational messages encouraging greater physical activity and a healthier diet have been only modestly successful. The best outcomes have been with children's programs that have high levels of physical activity.
Prevention is far superior to any available treatment for obesity. Obesity can be prevented by eating a healthy diet, being physically active, and making lifestyle changes that help maintain a normal weight. Examples include:
For many years experts recommended monitoring fat consumption and counting calories to prevent weight gain. The focus is gradually changing to reducing sugar intake and refined carbohydrate consumption and replacing saturated fats with unsaturated fats, as research indicates that these changes can help to reduce markers of metabolic syndrome. The current USDA dietary guidelines do not recommend a specifically low-fat diet, and counsel that 35% of calories can come from fat.
There have been calls for governments to change their dietary guidelines in an effort to address the obesity epidemic. Dr. David Harper, for example, has called on Canada to revise its dietary guidelines to recognize that low-fat diets are not supported by science, and that recent research supports the reduction of carbohydrates to treat diabetes and obesity. Experts in the United States have made the same plea to Congress, requesting that future dietary recommendations be based in sound science that has actually examined the effects of fat versus carbohydrate consumption. Others argue that recommendations in many countries to consume a moderate fat diet (up to 35% energy from fat) and to replace saturated fats with unsaturated fats and refined carbohydrates with complex carbohydrates are based on sound science.
It has been suggested that there may be little benefit in encouraging weight loss in older people, especially when there are no obesity-related complications or when promoting changes in lifelong eating habits creates stress. Studies have shown, however, that weight loss in seniors can lower the incidence of arthritis, diabetes, and other conditions, reduce cardiovascular risk factors, and improve well being. Increased physical activity in the elderly also improves muscle strength and endurance.
The poor prognosis for reversing adult obesity makes childhood prevention imperative. Unhealthy eating patterns and behaviors associated with obesity can be addressed by programs in nutrition, exercise, and stress management involving the entire family.
See also Bariatric surgery ; Body mass index ; Childhood obesity ; Coronary heart disease ; Diabetes mellitus ; Diet and disease prevention ; Diet drugs ; Dietary counseling ; Eating disorders ; Healthy People 2020 ; Maternal obesity .
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American Society for Metabolic and Bariatric Surgery, 100 SW 75th St., Ste. 201, Gainesville, FL, 32607, (352) 331-4900, Fax: (352) 331-4975, firstname.lastname@example.org, http://asmbs.org .
Center for Nutrition Policy and Promotion, U.S. Department of Agriculture, 3101 Park Center Drive, 10th Fl., Alexandria, VA 22302, (202) 720-2791, email@example.com, http://www.cnpp.usda.gov .
Obesity Medicine Association, 101 University Blvd., Ste. 330, Denver, CO, 80206, (303) 770-2526, Fax: (303) 779-4834, firstname.lastname@example.org, https://obesitymedicine.org .
Obesity Prevention Center, University of Minnesota, 1300 S Second St., Ste. 300, Minneapolis, MN, 55454, (612) 625-6200, email@example.com, http://www.ahc.umn.edu/opc/home.html .
Weight-Control Information Network, National Institute of Diabetes and Digestive and Kidney Diseases Health Information Center, 9000 Rockville Pike, Bethesda, MD, 20892, (800) 860-8747, firstname.lastname@example.org, https://www.niddk.nih.gov/health-information/communication-programs/win .
Rosalyn Carson-DeWitt, MD
Revised by Amy Hackney Blackwell, PhD