Obesity is a complex disorder involving an excessive amount of body fat. Obesity isn’t just a cosmetic concern. It increases your risk of diseases and health problems such as heart disease, diabetes and high blood pressure.

Being extremely obese means you are especially likely to have health problems related to your weight.

The good news is that even modest weight loss can improve or prevent the health problems associated with obesity. Dietary changes, increased physical activity and behavior changes can help you lose weight. Prescription medications or weight-loss surgery also may be options for treating obesity.

Obesity is likely when an individual’s body mass index (BMI) is 30 or higher. Your body mass index is calculated by dividing your weight in kilograms (kg) by your height in meters (m) squared.

BMI Weight status
Below 18.5 Underweight
18.5-24.9 Normal
25.0-29.9 Overweight
30.0-34.9 Obese (Class I)
35.0-39.9 Obese (Class II)
40.0 and higher Extreme obesity (Class III)

For most people, BMI is a reasonable estimate of body fat. However, BMI doesn’t directly measure body fat, so some people, such as muscular athletes, may have a BMI in the obese category even though they don’t have excess body fat. Ask your health care provider if your BMI is a problem.

When to see a doctor

If you think you may be obese, and especially if you’re concerned about weight-related health problems, see your doctor or health care provider. You and your provider can evaluate your health risks and discuss your weight-loss options.

Although there are genetic and hormonal influences on body weight, obesity occurs when you take in more calories than you burn through exercise and normal daily activities. Your body stores these excess calories as fat. Obesity usually results from a combination of causes and contributing factors, including:

  • Inactivity. If you’re not very active, you don’t burn as many calories. With a sedentary lifestyle, you can easily take in more calories every day than you use through exercise and normal daily activities.
  • Unhealthy diet and eating habits. Having a diet that’s high in calories, lacking in fruits and vegetables, full of fast food, missing breakfast, and laden with high-calorie beverages and oversized portions all contribute to weight gain.
  • Pregnancy. During pregnancy, a woman’s weight necessarily increases. Some women find this weight difficult to lose after the baby is born. This weight gain may contribute to the development of obesity in women.
  • Lack of sleep. Too little sleep can cause changes in hormones that increase your appetite. You may also crave foods high in calories and carbohydrates, which can contribute to weight gain.
  • Certain medications. Some medications can lead to weight gain if you don’t compensate through diet or activity. These medications include some antidepressants, anti-seizure medications, diabetes medications, antipsychotic medications, corticosteroids and beta blockers.
  • Medical problems. Obesity can sometimes be traced to a medical cause, such as Prader-Willi syndrome, Cushing’s syndrome, and other diseases and conditions. Some medical problems, such as arthritis, can lead to decreased activity, which may result in weight gain. A low metabolism is unlikely to cause obesity, as is having low thyroid function.

Obesity occurs when you eat and drink more calories than you burn through exercise and normal daily activities. Your body stores these extra calories as fat. Obesity usually results from a combination of causes and contributing factors, including:

  • Genetics. Your genes may affect the amount of body fat you store and where that fat is distributed. Genetics may also play a role in how efficiently your body converts food into energy and how your body burns calories during exercise. Even when someone has a genetic predisposition, environmental factors ultimately make you gain more weight.
  • Family lifestyle. Obesity tends to run in families. That’s not just because of genetics. Family members tend to have similar eating, lifestyle and activity habits. If one or both of your parents are obese, your risk of being obese is increased.
  • Inactivity. If you’re not very active, you don’t burn as many calories. With a sedentary lifestyle, you can easily take in more calories every day than you burn off through exercise and normal daily activities.
  • Unhealthy diet and eating habits. A diet that’s high in calories, lacking in fruits and vegetables, full of fast food, missing breakfast, and laden with high-calorie beverages and oversized portions contributes to weight gain.
  • Quitting smoking. Quitting smoking is often associated with weight gain. And for some, it can lead to enough weight gain that the person becomes obese. In the long run, however, quitting smoking is still a greater benefit to your health than continuing to smoke.
  • Pregnancy. During pregnancy, a woman’s weight necessarily increases. Some women find this weight difficult to lose after the baby is born. This weight gain may contribute to the development of obesity in women.
  • Lack of sleep. Not getting enough sleep or getting too much sleep at night can cause changes in hormones that increase your appetite. You may also crave foods high in calories and carbohydrates, which can contribute to weight gain.
  • Certain medications. Some medications can lead to weight gain if you don’t compensate through diet or activity. These medications include some antidepressants, anti-seizure medications, diabetes medications, antipsychotic medications, steroids and beta blockers.
  • Age. Obesity can occur at any age, even in young children. But as you age, hormonal changes and a less active lifestyle increase your risk of obesity. In addition, the amount of muscle in your body tends to decrease with age. This lower muscle mass leads to a decrease in metabolism. These changes also reduce calorie needs and can make it harder to keep off excess weight. If you don’t control what you eat and consciously become more physically active as you age, you’ll likely gain weight.
  • Social and economic issues. Certain social and economic issues may be linked to obesity. You may not have safe areas to exercise, you may not have been taught healthy ways of cooking or you may not have money to buy healthier foods. In addition, the people you spend time with may influence your weight — you’re more likely to become obese if you have obese friends or relatives.
  • Medical problems. Obesity can rarely be traced to a medical cause, such as Prader-Willi syndrome, Cushing’s syndrome, and other diseases and conditions. Some medical problems, such as arthritis, can lead to decreased activity, which may result in weight gain.

Even if you have one or more of these risk factors, it doesn’t mean that you’re destined to become obese. You can counteract most risk factors through diet, physical activity and exercise, and behavior changes.

If you’re obese, you’re more likely to develop a number of potentially serious health problems, including:

  • High triglycerides and low high-density lipoprotein (HDL) cholesterol
  • Type 2 diabetes
  • High blood pressure
  • Metabolic syndrome — a combination of high blood sugar, high blood pressure, high triglycerides and low HDL cholesterol
  • Heart disease
  • Stroke
  • Cancer, including cancer of the uterus, cervix, endometrium, ovaries, breast, colon, rectum, esophagus, liver, gallbladder, pancreas, kidney and prostate
  • Breathing disorders, including sleep apnea, a potentially serious sleep disorder in which breathing repeatedly stops and starts
  • Gallbladder disease
  • Gynecologic problems, such as infertility and irregular periods
  • Erectile dysfunction and sexual health issues
  • Nonalcoholic fatty liver disease, a condition in which fat builds up in the liver and can cause inflammation or scarring
  • Osteoarthritis
  • Skin conditions, including poor wound healing

Quality of life

When you’re obese, your overall quality of life may be lower, too. You may not be able to do things you’d normally enjoy as easily as you’d like, such as participating in enjoyable activities. You may avoid public places. Obese people may even encounter discrimination.

Other weight-related issues that may affect your quality of life include:

  • Depression
  • Disability
  • Sexual problems
  • Shame and guilt
  • Social isolation
  • Lower work achievement

If your BMI is in the overweight or obese range, your health care provider will typically review your health history in detail, perform a physical exam and recommend some tests.

These exams and tests generally include:

  • Taking your health history. Your doctor may review your weight history, weight-loss efforts, exercise habits, eating patterns, what other conditions you’ve had, medications, stress levels and other issues about your health. Your doctor may also review your family’s health history to see if you may be predisposed to certain conditions.
  • Checking for other health problems. If you have known health problems, your doctor will evaluate them. Your doctor will also check for other possible health problems in the examination and laboratory tests, such as high blood pressure and diabetes.
  • Calculating your BMI. Your doctor will check your body mass index (BMI) to determine your level of obesity. This should be done at least once a year. Your BMI also helps determine your overall health risk and what treatment may be appropriate.
  • Measuring your waist circumference. Fat stored around your waist, sometimes called visceral fat or abdominal fat, may further increase your risk of diseases such as diabetes and heart disease. Women with a waist measurement (circumference) of more than 35 inches (88 centimeters, or cm) and men with a waist measurement of more than 40 inches (102 cm) may have more health risks than do people with smaller waist measurements. Like the BMI measurement, your waist circumference should be checked at least once a year.
  • A general physical exam. This includes measuring your height; checking vital signs, such as heart rate, blood pressure and temperature; listening to your heart and lungs; and examining your abdomen.
  • Blood tests. What tests you have depend on your health, risk factors and any current symptoms you may be having. Tests may include a cholesterol test, liver function tests, fasting glucose, a thyroid test and others, depending on your health situation. Your doctor may also recommend certain heart tests, such as an electrocardiogram.

Gathering all this information helps you and your doctor determine how much weight you need to lose and what health conditions or risks you have. And this will shape what treatment options are right for you.

Numerous dietary supplements that promise to help you shed weight quickly are available. The effectiveness, particularly the long-term effectiveness, and safety of these products are often questionable. Talk to your doctor before taking any dietary supplements.

Herbal remedies, vitamins and minerals, all considered dietary supplements by the Food and Drug Administration, don’t have the same rigorous testing and labeling process as over-the-counter and prescription medications. Yet some of these substances, including products labeled as “natural,” have drug-like effects that can be dangerous. Even some vitamins and minerals can cause problems when taken in excessive amounts. Ingredients may not be standard, and they can cause unpredictable and harmful side effects. Dietary supplements can also cause dangerous interactions with prescription medications you take.

Green tea has been touted as a weight-loss aid, but a recent review of the research found little to no benefit from green tea for weight loss.

Mind-body therapies — such as acupuncture, mindfulness meditation and yoga — may complement other obesity treatments. However, these therapies generally haven’t been well-studied in the treatment of weight loss. Talk to your doctor if you’re interested in adding a mind-body therapy to your treatment.

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