Medically Reviewed By William C. Lloyd III, MD, FACS

What is obesity?

Obesity is a common condition in which there is an excessive amount of body fat to a degree that puts a person at risk for serious chronic health problems, such as diabetes or hypertension. Obesity is a major health epidemic that affects all populations, regardless of gender or race, and it is becoming more common in children as well as adults.

A person is generally considered obese if he or she has a body mass index (BMI) greater than 30. The Centers for Disease Control and Prevention (CDC) estimates that about 34% of the U.S. adult population is obese and 5.9% is extremely obese.

Obesity is caused by consuming more calories than the body metabolizes (burns off) for energy over a period of time. However, the risk factors that determine obesity can be a complex combination of genetics, socioeconomic factors, metabolic factors, and lifestyle choices. Some endocrine disorders, diseases, and medications may also exert a powerful influence on an individual's weight.

Obesity is not necessarily the same thing as being overweight. Overweight is defined as weighing more than what is generally considered normal based on your height. However, being overweight can occasionally be caused by increased muscle size or water retention and does not always mean that someone is unhealthy. For example, some athletes may be considered overweight because of having developed muscles, which weigh more than fat, while still having a healthy level of body fat.

Obesity can take a major toll on your physical health, affecting virtually every organ and body system, including the musculoskeletal, cardiovascular, respiratory, digestive and reproductive systems. The good news is that losing even 5 to 10% of your weight can delay or prevent obesity-related diseases.

Obesity increases the risk for dangerous conditions, such as diabetes, heart disease, arthritis, and cancer. Seek prompt medical care if you experience weight gain. Following a medically recommended weight loss plan can help you reduce the risk of serious diseases associated with obesity.

What are the symptoms of obesity?

General symptoms of obesity include weight gain, needing to buy progressively larger-sized clothing, and a change in the shape of your body due to the accumulation of excessive fat. In men, excessive fat stores tend to accumulate in the waist. In women, extra fat is often stored in the hips and thighs. However, in both sexes, extra fat can accumulate throughout the body, including such areas as the face, neck, feet and hands.

Body mass index and other measures

A medical sign of obesity or overweight is having a higher than normal body mass index (BMI). BMI is one method used by healthcare professionals to calculate an estimate of the amount of body fat you are carrying. BMI is accurate for most people, but may not be an accurate indicator of excessive fat stores for certain populations.

For example, if you are an athlete with developed muscles, which weigh more than fat, you may have a healthy level of body fat but still rank as overweight on the BMI. Also, BMI is not accurate in determining fat stores in pregnant women and people with diseases that cause moderate to large amounts of water retention.

While a high BMI identifies potential weight issues, it is not enough to diagnose obesity and will not indicate any specific health risks. To better determine the risk of developing weight-related health problems, other indicators are assessed by healthcare providers. These include:

  • Obesity-related diseases and conditions, such as high blood pressure or a sedentary lifestyle, and other factors
  • Waist size, as excessive fat in the waistline is associated with an increased risk for obesity-related diseases, such as diabetes

What causes obesity?

Obesity is caused by consuming more calories than necessary to fuel your body’s activity level and metabolic processes in a given time period. Extra calories are stored as fat if there is not a corresponding increase in activity to burn calories.

Primary causes of an increase in stored body fat include:

  • Diets that are high in calories, fat and sugar
  • Sedentary lifestyle without sufficient exercise

Less often, obesity may be directly or indirectly caused by certain untreated diseases or conditions including:

  • Certain medications, such as corticosteroids, antidepressants, and seizure medications
  • Cushing syndrome (overproduction of the hormone cortisol)
  • Polycystic ovarian syndrome (PCOS, which produces high levels of certain hormones)

Is obesity genetic?

Although researchers have identified several genes that appear to be associated with obesity, most believe that one single gene is not responsible for the entire obesity epidemic.

However, studies have shown that a predisposition toward obesity can be inherited. Studies of identical twins, including those who have been raised separately, have estimated that inheritability of obesity can be as high as 77%. In rare cases, genetic defects in children can affect production of hormones related to appetite stimulation, such as leptin, which can result in severe obesity.

Scientists also have proposed a “thrifty genotype” hypothesis based on our ancestors’ lack of regular access to food. This theory suggests that the human body is “trained” to retain weight rather than lose it, which can make it difficult to maintain a healthy weight in environments where food—and high-calorie food, at that—is readily available.

Along with genetics, lifestyle factors within families play a role in obesity, as children are more likely to model eating or exercise habits from those of the people around them.

What are the risk factors for obesity?

There are many factors that may encourage, influence or contribute to the development of obesity. These factors may occur alone or may be linked with other factors, such as aging in combination with a sedentary lifestyle.

Factors that can increase the risk of obesity include:

  • Aging, which slows metabolism and the rate at which you burn calories
  • Cultural factors, such as overeating or eating high-calorie foods as a part of certain cultural practices or gatherings
  • Eating a diet that is high in calories, fat and sugar. Your caloric intake may be influenced by the easy accessibility of super-sized, high-calorie foods, which also tend to be less expensive and more convenient than healthier foods.
  • Family history of obesity. Obesity tends to run in families, which may be linked to both genetics and the development of similar dietary and exercise habits.
  • Pregnancy
  • Poor socioeconomic status. People from low-income backgrounds have a greater risk for obesity.
  • Sedentary lifestyle
  • Smoking cessation. Some people who quit smoking gain weight. After quitting smoking, the sense of taste and smell improves, which may encourage some people to overeat.
  • Stress, depression, anxiety, and other mental and emotional disturbances
  • Weight gain during pregnancy that is not lost after giving birth
  • Working night shifts or odd shifts and getting poor-quality sleep

There is a strong relationship between economic status and obesity, especially among women. Women who are poor and of lower social status are more likely to be obese than women of higher socioeconomic status. The occurrence of obesity is also highest among minority groups, especially among women.

Overeating, along with a sedentary lifestyle, contributes to obesity. These are lifestyle choices that can be affected by behavior change. Eating a diet in which a high percentage of calories come from sugary, high-fat, refined foods promotes weight gain. Lack of regular exercise contributes to obesity in adults and makes it difficult to maintain weight loss. In children, inactivity, such as watching television, playing too many video games, or sitting at a computer, contributes to obesity.

Reducing your risk of obesity

You may be able to lower your risk of obesity and its complications by:

  • Eating a healthy diet focusing on low-calorie, high-nutrient foods, including lean meats, fruits, vegetables and whole grains. Avoid processed foods high in saturated fats, and limit alcohol and sweets to occasional treats.
  • Exercising regularly, ideally 150 to 300 minutes per week of moderate-intensity activity, such as tennis, biking, dancing, gardening, swimming or brisk walking
  • Finding weight-loss support through friends or online groups, to help stay motivated and keep yourself accountable
  • Getting quality sleep, ideally 7 to 8 hours each night. Sleep deprivation can cause increased appetite, and loss of sleep can make losing weight more difficult. Conversely, conditions caused by obesity, such as sleep apnea, can result in poor sleep.
  • Lowering stress through activities, such as meditation and mindfulness. Stress hormones, such as cortisol, can cause weight gain. Feelings of stress can also lead to overeating, particularly of comfort foods that are high in fat and sugar.
  • Monitoring your weight to be aware of your progress and to identify weight gain patterns based on your diet and activity

Losing 1 to 2 pounds a week is considered a healthy rate of weight loss. Avoid weight-loss fads or “crash” diets that can be unhealthy and are not sustainable. For some people, intermittent fasting can be an effective tool for managing diet when done properly. Your doctor can work with you to establish weight loss goals and guide you toward resources and support to help you achieve them.

What are the diet and nutrition tips for obesity?

Healthy eating habits are essential to addressing obesity and to achieving and maintaining a healthy weight. By working with your doctor and possibly a nutritionist, you can determine your target daily calorie intake and build a nutrition plan that meets your weight loss goals.

A nutritious diet includes not just what you eat, but also how much and when you eat. Tips for diet and nutrition with a goal of weight loss or healthy weight maintenance include:

  • Avoiding processed foods, such as fast food, potato chips, packaged cookies, and frozen pizza
  • Cooking meals yourself, to help control ingredients and manage portions
  • Drinking plenty of water, while avoiding high-sugar beverages, such as regular soda, sweetened tea, or fruit juice. Be wary of sports drinks, too, as they include high amounts of sugar.
  • Eating a healthy breakfast every morning to avoid overeating later in the day
  • Focusing on whole foods that are minimally processed, including whole grains, colorful vegetables, whole fruits, lean fish and poultry, nuts and seeds, and plant oils, such as olive oil
  • Keeping a food journal to monitor your eating habits and make changes where necessary. Even if you don’t track every calorie, it helps to have an awareness of what—and how much—you are eating each day.
  • Limiting alcohol, which contains “empty” calories and can make you more likely to overeat
  • Limiting refined grains and sugars, including white bread, white pasta, and white rice
  • Reducing red meat in favor of lean poultry or fish. Cut back on cold cuts too, which add sodium and preservatives. A piece of fresh roasted turkey is healthier than packaged turkey from the deli.
  • Slowing down and eating smaller portions, to give your body time to tell you when it’s had enough food. This can also help improve mindful eating, which allows you to focus on making good choices and savor the food in front of you.

How do doctors diagnose obesity?

Your doctor likely measures your weight at each of your appointments. If your weight increases significantly over time, he or she may discuss factors that could be contributing to your weight gain.

The most common screening tool for overweight and obesity is body mass index (BMI). Doctors calculate this measure using a formula based on your weight and height. In adults, a BMI from 18.5 to 24.9 is considered normal while a BMI of more than 25 is considered overweight. A person is considered obese if the BMI is greater than 30 and morbidly obese if the BMI is 40 or greater. When assessing a child's weight, the BMI is calculated and then plotted on a BMI for age percentile curve.

It’s important to note that a high BMI does not necessarily mean someone’s weight is unhealthy. For example, some people may have a lot of muscle, which is denser than fat. This means they have a higher weight, and thus a higher BMI, but their body fat remains low.

Another measure of obesity is the waist-to-hip ratio (WHR). The WHR is a measurement tool that looks at the proportion of fat stored on the waist, and hips and buttocks. The waist circumference indicates abdominal fat. A waist circumference more than 40 inches in men and more than 35 inches in women may increase the risk of heart disease and other diseases associated with being overweight.

What are the treatments for obesity?

In most cases, obesity in adults and children results from consuming too many calories and not getting enough physical activity. Treatment of obesity includes developing and following a sensible, comprehensive lifelong plan to reduce your caloric intake while ensuring good nutrition and hydration, and increasing physical activity.

Effective weight loss plans often incorporate some form of support through a medically approved weight loss group or organization, such as Weight Watchers. Counseling may also be recommended to help you change certain behaviors or address issues that lead you to overeat, such as anxiety and depression.

In general, experts advise that you lose no more than 1 to 2 pounds a week to achieve a safe, healthy weight loss that can be maintained. Recommended calorie intake and exercise levels will vary among individuals, depending on age, sex, general fitness level, medical history, and other factors. Very low-calorie diets or diets that are not well-balanced are generally not recommended because they can lead to rebound weight gain, poor nutrition, and other health problems.

Consult with your healthcare provider before starting any weight reduction plan so he or she can monitor health conditions, such as blood pressure and blood sugar levels, and help you develop the most effective, safe and healthy weight-loss plan for you. Your provider or weight loss support group will help set you up for success with realistic expectations in the days, weeks and months ahead.

Medications used to treat obesity

When a comprehensive diet and exercise program is not enough to help a severely obese person lose weight, medications or surgery may be an option to help treat obesity. ‘

You should not take any weight-reduction medications, supplements, or herbal preparations without first consulting with your physician or healthcare provider. Over-the-counter (OTC) products may cause serious side effects or interactions with the medications you take and many have not been tested by the Food and Drug Administration (FDA) to prove they are safe or effective.

The FDA has approved these weight loss medications:

  • Contrave is the brand name for a combination of bupropion (an antidepressant that can decrease appetite) and naltrexone (an anti-addiction drug that can also suppress hunger). People who take or have taken opioid medications, or those in recovery from alcohol or drug addiction, should avoid Contrave.
  • Orlistat, sold under the brand names Alli (60 mg dose, OTC) and Xenical (120 mg dose, prescription), is a medication that reduces the absorption of fats; fat calories; and vitamins A, D, E and K by the body. Rare cases of liver injury or liver failure have been reported with both forms of orlistat.
  • Qsymia is the brand name for an extended-release combination of phentermine (an appetite suppressant) and topiramate (an antiepileptic drug that has a side effect of weight loss). Women who are or may become pregnant should avoid Qsymia, as it can increase the risk of birth defects. Qsymia may also interact with certain MAOI (monoamine oxidase inhibitor) antidepressants.

Surgical procedures used to treat obesity

Weight loss surgery, or bariatric surgery, may help some seriously obese people who have not lost weight by attempting lifestyle and dietary changes, or who have serious complications of obesity, such as type 2 diabetes or cardiovascular disease. Typically, these procedures target the gastrointestinal (GI) tract, reducing the amount of absorbable nutrients.

The most common surgical methods include:

  • Gastric band, or Lap-Band, involves placing a band around the upper portion of the stomach to make a smaller pouch for food, which limits how much food you can eat and makes you feel full sooner.
  • Roux-en-Y gastric bypass involves creating a small stomach pouch with a bypass around part of the small intestine, which is where most calories are absorbed.
  • Sleeve gastrectomy, also known as vertical sleeve gastrectomy, removes about 80% of the stomach, restricting the amount of food you can consume. This procedure is for people with severe obesity (a BMI of 40 or higher) and in rare cases is paired with an intestinal bypass that limits the absorption of proteins and fats.

What are the potential complications of obesity?

Complications of obesity can be serious, even life-threatening. You can treat obesity and minimize the risk of complications by following the treatment plan you and your healthcare professional design specifically for you.

Potential complications of obesity include:

  • Cancer including prostate, rectum, colon, ovaries, uterus, cervix and breast
  • Depression and other mental and emotional issues
  • Disability
  • Gallbladder disease
  • Gynecologic problems, such as infertility and irregular periods
  • Hyperlipidemia
  • Skin problems, such as impaired wound healing
  • Thromboembolism
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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Mar 8
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