Obesity

In technologically advanced countries, lack of physical activity is common and contributes to the increase in obesity. Opportunities for physical activity have been engineered away by technological advances, such as elevators, cars, and remote controls. More time is spent doing sedentary activities, such as using the computer, watching television, and playing video games. Also, people’s jobs have become more sedentary as office or desk jobs have replaced manual labor. Sedentary people use fewer calories than more active people and thus require fewer calories in the diet. If caloric intake is not reduced accordingly, people gain weight.

Energy-dense foods, which are foods that have a large number of calories in a relatively small amount (volume), promote weight gain. Most of these foods contain more processed carbohydrates, more fat, and less fiber. Fats, by nature, are energy dense. Fat has 9 calories per gram, but carbohydrates and proteins have 4 calories per gram. Energy-dense foods are common in technologically advanced countries.

Convenience foods, such as energy-dense snacks offered at vending machines and fast food restaurants, contribute to the increase in obesity. High-calorie beverages, including soda, juices, many coffee drinks, and alcohol, also contribute significantly. For example, a 12-ounce soda or bottle of beer has 150 calories, and a 12-ounce coffee beverage (containing dairy and sugar) or fruit smoothie can have 500 or more calories. High-fructose corn syrup (used to sweeten many bottled beverages) is often singled out as being particularly likely to cause obesity. However, recent studies show that it is no more likely to cause obesity than other foods with a similar number of calories in sugar.

Larger portion sizes at restaurants and in packaged foods and beverages encourage people to overeat. Also, restaurant and packaged foods are often prepared in ways that add calories. As a result, people may consume more calories than they realize.

Obesity tends to run in families. Genes help determine body mass index (BMI) in over 60% of people. However, families share not only genes Genes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body or the code for functional ribonucleic... read more but also environment, and separating the two influences is difficult. Genes can affect how quickly the body burns calories at rest and during exercise. They can also affect appetite and thus how much food is consumed. Genes may have a greater effect on where body fat accumulates, particularly fat around the waist and in the abdomen, than on how much body fat accumulates.

Many genes influence weight, but each gene has only a very small effect. Obesity rarely results when only one gene is abnormal.

Rarely, mutations in the following genes result in obesity:

Certain characteristics can increase the risk of becoming overweight or obese. They include the following:

Adverse childhood events or a childhood history of verbal, physical, or sexual abuse are associated with a higher risk of obesity. According to the Centers for Disease Control and Prevention's adverse childhood events study, a history of verbal, physical, or sexual abuse during childhood increases the risk of obesity by 8% and the risk of severe obesity by 17.3%.

Gaining weight during pregnancy is normal and necessary. However, pregnancy can be the beginning of weight problems if women do not return to their prepregnancy weight. About 15% of women permanently gain 20 pounds or more with each pregnancy. Having several children close together may compound the problem. Breastfeeding can help women return to their prepregnancy weight.

If a pregnant woman is obese or smokes, weight regulation may be disturbed, contributing to weight gain during childhood and later.

After menopause Menopause Menopause is the permanent end of menstrual periods, ovulation, and fertility. For up to several years before and just after menopause, estrogen levels fluctuate widely, periods become irregular... read more , many women gain weight. This weight gain may result from reduced activity. Hormonal changes may cause fat to be redistributed and accumulate around the waist. Fat in this location increases the risk of health problems (such as metabolic syndrome Metabolic Syndrome Metabolic syndrome is characterized by a large waist circumference (due to excess abdominal fat), high blood pressure, resistance to the effects of insulin (insulin resistance) or diabetes,... read more ).

Obesity becomes more common as people age (see Obesity in Older Adults Obesity is a chronic, recurring complex disorder characterized by excess body weight. Obesity is influenced by a combination of factors that includes genetics, hormones, behavior, and the environment... read more ). As people age, body composition may change as muscle tissue decreases. The result is a higher percentage of body fat and a lower basal metabolic rate (because muscle burns more calories).

Sleep deprivation or lack of sleep (usually considered less than 6 to 8 hours per night) can result in weight gain. Sleeplessness results in hormonal changes that increase appetite and cravings for energy-dense foods.

Stopping smoking usually results in weight gain and may deter people from stopping smoking. Nicotine decreases appetite and increases the metabolic rate. When nicotine is stopped, people may eat more food, and their metabolic rate decreases, so that fewer calories are burned. As a result, body weight may increase by 5 to 10%.

Hormonal disorders rarely cause obesity. The following are among the most common:

Two eating disorders are associated with obesity:

Many medications used to treat common disorders promote weight gain. These medications include those used to treat the following:

Having obesity increases the risk of many health problems. Virtually every organ system can be affected. These weight-related health problems can cause symptoms, such as shortness of breath, difficulty breathing during activity, snoring, skin abnormalities including stretch marks, and joint and back pain.

Obesity increases the risk of the following:

Obstructive sleep apnea Sleep Apnea Sleep apnea is a serious disorder in which breathing repeatedly stops long enough to disrupt sleep and often temporarily decrease the amount of oxygen and increase the amount of carbon dioxide... read more can develop if excess fat in the neck compresses the airway during sleep. Breathing stops for a few moments, as often as hundreds of times a night. This disorder is often undiagnosed. It can cause loud snoring and excessive daytime sleepiness and increases the risk of high blood pressure Metabolic Syndrome Metabolic syndrome is characterized by a large waist circumference (due to excess abdominal fat), high blood pressure, resistance to the effects of insulin (insulin resistance) or diabetes,... read more , abnormal heart rhythms Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more , metabolic syndrome Metabolic Syndrome Metabolic syndrome is characterized by a large waist circumference (due to excess abdominal fat), high blood pressure, resistance to the effects of insulin (insulin resistance) or diabetes,... read more , heart attacks Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more , heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more , and strokes Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more .

Obesity can increase the risk of early death. The more severe the obesity, the higher the risk. It is the second most common cause of preventable death (cigarette smoking is the most common). Studies indicate that over a period of 15 years, the death rate is 30% lower for people who had weight loss surgery than for people who had not had it.

Obesity can lead to social, economic, and psychologic problems. For example, people with obesity may be underemployed or unemployed, or they may have a poor body image and low self-esteem.

If untreated, obesity tends to worsen, increasing the risk and severity of complications.

After weight loss, most people return to their pretreatment weight within 5 years. Also, when weight-loss medications are stopped, weight tends to be gained back.

Healthy, balanced eating for weight loss requires reducing the number of calories consumed and choosing a wide range of foods that provide good nutrition.

Reducing the number of calories consumed by 500 to 1,000 calories a day may result in a weight loss of 1 to 2 pounds per week, which is a healthy rate of weight loss. This approach usually means consuming 1,200 to 1,500 calories a day. However, the body may adjust to the decrease in calories (for example, by decreasing the metabolic rate). Thus, weight loss may be less than expected. Still, consuming a high-fiber diet plus reducing the number of calories by about 600 calories a day and substituting some carbohydrate for protein appears to be the best way to lose weight and keep it off. Weight can be lost more rapidly with a very low calorie diet, but such diets should be supervised by a doctor.

The following changes in diet are recommended:

Eating foods with a low glycemic index Glycemic index Carbohydrates, proteins, and fats are the main types of macronutrients in food (nutrients that are required daily in large quantities). They supply 90% of the dry weight of the diet and 100%... read more and foods that contain fish oils (including deep-sea fish such as salmon and tuna) or monounsaturated fats derived from plants (such as olive oil) may reduce the risk of heart disorders and diabetes Prevention Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Symptoms of diabetes may... read more .

No-fat or low-fat dairy products, which provide vitamin D, should be included to help prevent a deficiency of this vitamin.

Using meal replacements, regularly or once in a while, can help some people lose weight and keep it off.

Increasing physical activity can help people lose weight in a healthy way and keep it off. Physical activity includes not only exercise (that is, structured physical activity) but also lifestyle activities, such as taking the stairs instead of the elevator, gardening, and walking instead of driving when possible. Lifestyle activities can burn a considerable number of calories. People who do not exercise while dieting are more likely to regain the weight they lose.

Aerobic exercise, such as jogging, walking briskly (3 to 4 miles an hour), biking, singles tennis, skating, and cross-country skiing, burn more calories than less active exercises (see Choosing the Right Exercise There are many forms of exercise, and each type has its advantages and disadvantages. Some types of exercise expend more calories than others (see table ). Different forms of exercise (for example... read more ). For example, vigorous walking can burn about 4 calories per minute, so that 1 hour of brisk walking per day burns about 240 calories. Running burns about 6 to 8 calories per minute (about 360 to 480 calories per hour). As a general guide, people need to walk at least 150 minutes each week to promote health. To lose weight and keep it off, people need to spend 300 to 360 minutes each week doing moderate physical activity or 150 minutes each week doing vigorous aerobic exercise (such as running or using an elliptical machine). Other health benefits of vigorous aerobic exercise Benefits of Exercise Regular exercise makes the heart stronger and the lungs fitter, enabling the cardiovascular system to deliver more oxygen to the body with every heartbeat and the pulmonary system to increase... read more include reducing the risk of coronary artery disease Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more and increasing endurance.

To get the most benefit from exercise, people should do strength training (with weights or another form of resistance) about 3 days of the week. Strength training increases the amount of muscle tissue, which increases the metabolic rate, so that the body burns more calories when at rest.

Ultimately, for weight loss to be effective and long-lasting, people must change their behavior. Weight-loss programs that help people change their behavior are the most effective. To change behavior, people need certain skills, such as

Problem solving involves identifying and planning ahead for situations that make unhealthy eating more likely (such as going out to dinner or traveling) or that reduce the opportunity for physical activity (such as driving cross country).

To manage stress, people can learn to identify stressful situations and develop ways to manage the stress that do not involve eating—for example, by going for a walk, meditating, or taking deep breaths.

To monitor themselves, people may keep a food log, including the number of calories in the foods, and weigh themselves regularly. They may record where and when they eat, what their mood is when they eat, and who is with them. With this information, they can observe and record patterns of behavior and eating and may be able to avoid situations that lead to weight gain or unhealthy eating.

Contingency management involves providing rewards (other than food) for behavior that contributes to weight loss or maintenance. For example, if people walk more or eat less of certain foods, they may reward themselves by getting new clothes or going to a movie. Rewards may also come from other people—for example, praise from family members or members of a support group. People can get support by using social media to connect with each other and health care professionals.

To control stimuli that can trigger unhealthy eating, people can learn to identify obstacles to healthy eating and an active lifestyle. Then they can develop strategies to overcome them. For example, people may avoid going by a fast food restaurant on their way to work or not keep sweets in the house. To develop an active lifestyle, they may take up an active hobby (such as gardening), walk more, make a habit of taking the stairs instead of elevators, or park at the far end of parking lots (resulting in a longer walk).

Internet resources, applications for mobile devices, and other technological devices may also help people develop an active lifestyle and maintain weight loss. Applications can help people set a weight-loss goal, monitor their progress, track food consumption, and record physical activity.

For people who have obesity or overweight and weight-related disorders, weight-loss medications (also called anti-obesity medications) can be useful. Medications are most effective when used with changes in diet, increased physical activity, and structured programs that include changes in behavior.

Some weight-loss medications are intended to be used for a short time. Others are intended to be used for a long time. Weight-loss medications should be stopped or changed if people do not lose weight after 12 weeks of treatment.

Anti-obesity medications that are currently available include

These medications are used if people have a body mass index (BMI) of 30 or higher or if people have a BMI of 27 or higher and have complications such as high blood pressure High Blood Pressure High blood pressure (hypertension) is persistently high pressure in the arteries. Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying... read more or diabetes Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Symptoms of diabetes may... read more . When people take weight-loss medications, they usually lose about 5 to 2% of their body weight.

Orlistat limits the breakdown and absorption of fats in the intestine, producing, in effect, a low-fat diet. Orlistat is available over the counter as well as by prescription. It results in unabsorbed fat in the digestive tract. This fat can cause bloating, gas, and loose stools, but these problems tend to resolve over time. Orlistat should be taken with meals that contain fat. Orlistat can interfere with the absorption of the fat-soluble vitamins Fat-soluble vitamins Vitamins are a vital part of a healthy diet. The recommended dietary allowance (RDA)—the amount most healthy people need each day to remain healthy—has been determined for most vitamins. A safe... read more : A, D, E, and K. If not enough vitamin D is absorbed, some people develop osteoporosis, making fractures more likely. People who take orlistat should take a vitamin supplement that contains these nutrients. The supplement should be taken at least 2 hours before or after taking orlistat.

Phentermine reduces appetite by affecting chemical messengers in the part of the brain that controls appetite. It is available by prescription only. It is taken only for a short time. It can increase blood pressure and heart rate and cause insomnia, anxiety, and constipation.

Phentermine plus topiramate (used to treat seizures and migraines) is available by prescription only. This combination results in weight loss for up to 2 years. However, it can cause birth defects, so women of childbearing age should take it only if they are using birth control and are tested monthly for pregnancy. These medications can cause problems with sleep and concentration and can increase heart rate.

Lorcaserin is given by prescription only. It is not available in the United States because of concerns about a possible increased risk of cancer. It suppresses appetite by affecting certain receptors in the brain. Side effects include headache, nausea, dizziness, fatigue, dry mouth, and constipation, but these effects tend to resolve over time. Pregnant women should not take locarserin. People who take lorcaserin should not take certain antidepressants (selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, and monoamine oxidase inhibitors).

Naltrexone plus bupropion is available by prescription only. It can help people lose weight when it is used with diet and exercise. Naltrexone is used alone to block the effects of opioids and to help alcoholics stop drinking alcohol. Naltrexone may also help curb hunger. Bupropion is used alone to treat depression and to help people stop smoking. Bupropion can also decrease appetite. Side effects of the combination medication include increased blood pressure, nausea, vomiting, and headache. People who have uncontrolled high blood pressure, who have had seizures, or who have a seizure disorder Seizure Disorders In seizure disorders, the brain's electrical activity is periodically disturbed, resulting in some degree of temporary brain dysfunction. Many people have unusual sensations just before a seizure... read more should not take this medication.

Liraglutide is used to treat type 2 diabetes Injectable Antihyperglycemic Medications Many people with diabetes require medication to lower blood glucose levels, relieve symptoms, and prevent complications of diabetes. There are two types of diabetes mellitus Type 1, in which... read more and obesity. Liraglutide works by slowing the passage of food from the stomach. It must be given by injection. Its side effects include headache, diarrhea, nausea, vomiting, inflammation of the pancreas (pancreatitis), and low blood sugar (hypoglycemia). People who have a type of thyroid cancer called medullary thyroid carcinoma Medullary thyroid cancer The cause of thyroid cancer is not known, but the thyroid gland is very sensitive to radiation, which may cause cancerous changes. Thyroid cancer is more common among people who were treated... read more should not take liraglutide.

Semaglutide is an injectable medication used to treat type 2 diabetes Injectable Antihyperglycemic Medications Many people with diabetes require medication to lower blood glucose levels, relieve symptoms, and prevent complications of diabetes. There are two types of diabetes mellitus Type 1, in which... read more and obesity. Semaglutide helps the pancreas release the right amount of insulin and is an appetite suppressant. Like liraglutide, the most common side effects of semaglutide include nausea and diarrhea. Semaglutide should not be used by people who have had or thyroid cancer called medullary thyroid cancer or have relatives who have had it. Also, people who have an endocrine system disorder called multiple endocrine neoplasia syndrome type 2 Multiple Endocrine Neoplasia Syndromes (MEN) Multiple endocrine neoplasia syndromes are rare, inherited disorders in which several endocrine glands develop noncancerous (benign) or cancerous (malignant) tumors or grow excessively without... read more (MEN 2) should not take semaglutide.

Tirzepatide is used to treat type 2 diabetes. It can cause substantial and sustained weight loss in adults who do not have diabetes. It also reduces the risk of heart and endocrine disorders. Tirzepatide is not yet approved for the treatment of obesity but is expected to be in the near future. Possible side effects include pancreatitis, low blood sugar, and thyroid tumors. People with multiple endocrine neoplasia syndrome type 2 should not take it.

Some over-the-counter diet aids, including medicinal herbs, claim to enhance weight loss by increasing metabolism or by increasing a feeling of fullness. These supplements have not been shown to be effective and may contain harmful additives or stimulants (such as ephedra, caffeine, guarana, and phenylpropanolamine) and should be avoided.