Obesity is commonly defined as having too much body mass. A BMI of 30 or higher is the usual benchmark for obesity in adults. A BMI of 40 or higher is considered severe (formerly “morbid”) obesity. Childhood obesity is measured against growth charts.
Obesity is a complex, chronic disease with several causes that lead to excessive body fat and sometimes, poor health. Body fat itself is not a disease, of course. But when your body has too much extra fat, it can change the way it functions. These changes are progressive, can worsen over time, and they can lead to adverse health effects.
The good news is that you can improve your health risks by losing some of your excess body fat. Even small changes in weight can have a big impact on your health. Not every weight loss method works for everyone. Most people have tried to lose weight more than once. And keeping the weight off is just as important as losing it in the first place.
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Healthcare providers commonly use the Body Mass Index (BMI) to define obesity in the general population. The BMI measures average body weight against average body height. As a generalization, healthcare providers associate a BMI of 30 or higher with obesity. Although BMI has its limitations, it’s an easily measurable indicator and can help alert you to obesity-related health risks.
Examples of limitations include bodybuilders and athletes, who have more muscle and may have higher BMI scores even though their fat levels are low. It’s also possible to have obesity at a “normal” weight. If your body weight is average but your body fat percentage is high, you may have the same health risks as somebody with a higher BMI.
Healthcare providers have also observed ethnic differences in how much extra weight different people can carry before it affects their health. For example, people of Asian descent are more likely to have health risks at a lower BMI, and Black people are more likely to have health risks at a higher BMI.
Another way of assessing obesity is by measuring waist circumference. If you have more body fat around your waist, you are statistically more at risk of obesity-related diseases. The risk becomes significant when your waist size is more than 35 inches for people assigned female at birth or 40 inches for people assigned male at birth.
Healthcare providers classify obesity into class types based on how severe it is. They use BMI to do it. If your BMI is between 25.0 and 29.9 kg/m², they put you in the overweight category. There are three general classes of obesity that healthcare providers use to evaluate what treatments may work best for each person. They include:
"Morbid obesity" is an outdated term for class III obesity. In medical language, “morbidity” means associated health risks. Doctors referred to class III obesity as “morbid” because it was most likely to come with related health problems. However, they retired the term because of its negative connotations.
Healthcare providers also use BMI to calculate obesity in children, but they calculate it relative to the child’s age and assigned sex. A child older than 2 years may be diagnosed with obesity if their BMI is greater than 95% of their peers in the same category. Different growth charts may present slightly different BMI averages, based on the population they are sampling.
Obesity in American adults was last surveyed in 2017-2018. The prevalence was 42.5%, up from 30.5% in 1999-2000. In that same period, the prevalence of class III obesity almost doubled from 4.7% to 9.2%. Childhood obesity in America from 2017-2018 was 19.3%.
Worldwide, obesity has nearly tripled in the last 50 years. The rise has been especially dramatic in lower-income countries where malnutrition is common. These communities now have greater access to higher-calorie foods with low nutritional value. Obesity now commonly coexists with undernutrition in these countries.
Obesity affects your body in many ways. Some are simply the mechanical effects of having more body fat. For example, you can draw a clear line between extra weight on your body and extra pressure on your skeleton and joints. Other effects are more subtle, such as chemical changes in your blood that increase your risk for diabetes, heart disease and stroke.
Some effects are still not well understood. For example, there is an increased risk of certain cancers with obesity. We don’t know why, but it exists. Statistically, obesity increases your risk of premature death from all causes. By the same token, studies show that you can significantly improve these risks by losing even a small amount of weight (5% to 10%).
Your metabolism is the process of converting calories into energy to fuel your body’s functions. When your body has more calories than it can use, it converts the extra calories into lipids and stores them in your adipose tissue (body fat). When you run out of tissue to store lipids in, the fat cells themselves become enlarged. Enlarged fat cells secrete hormones and other chemicals that produce an inflammatory response.
Chronic inflammation has many adverse health effects. One way that it affects your metabolism is by contributing to insulin resistance. This means your body can no longer use insulin to efficiently lower blood glucose and blood lipid levels (sugars and fats in your blood). High blood sugar and blood lipids (cholesterol and triglycerides) also contribute to high blood pressure.
Together, these combined risk factors are known as metabolic syndrome. They are grouped together because they all tend to reinforce each other. They also reinforce further weight gain and make it harder to lose weight and sustain weight loss. Metabolic syndrome is a common factor in obesity and contributes to many related diseases, including:
According to the U.S. Centers for Disease Control and Prevention, 1 in 3 adults with obesity also has arthritis. Studies have shown that for every 5 kg in weight gain, your risk of knee arthritis increases by 36%. The good news is that, together with exercise, weight loss of 10% can significantly reduce arthritis-related pain and improve your quality of life.
Obesity is also associated indirectly with:
On the most basic level, obesity is caused by consuming more calories than your body can use. Many factors contribute to this. Some factors are individual to you. Others are built into the structure of our society, either on a national, local or family level. In some ways, preventing obesity requires consciously working against these multiple factors.
Factors that may increase calorie consumption include:
Factors that may decrease how many calories we spend include:
Your healthcare provider will measure your weight, height and waist circumference at your appointment.
More importantly, when you come to your healthcare provider for care, they will want to know your whole health story. They will ask you about your history of medical conditions, medications and weight changes. They’ll also want to know about your current eating, sleeping and exercise patterns and stress factors and whether you have tried any weight loss programs in the past. They may ask about your biological family’s health history.
They will also examine your vital functions by taking your heart rate and blood pressure and listening to your heart and lungs. They may give you a blood test to check your blood glucose and cholesterol levels and screen for hormone problems. They'll use this complete profile to diagnose your obesity and any related conditions you might have.
Your complete health profile will determine your individual treatment plan. Your healthcare provider will target your most urgent health concerns first, then follow up with a longer-term weight loss plan. Sometimes there may be quick changes they can recommend for an immediate impact, like switching your medications. The overall treatment plan will be more gradual and probably involve many factors. Since everyone is different, it may take some trial and error to figure out which therapies work best for you. Studies have repeatedly shown that intense, team-based programs with frequent, personal communication between your provider and you are the most successful in helping people lose weight and keep it off.
Your treatment plan may include:
The dietary changes you personally need to make to lose weight will be individual to you. Some people may benefit from cutting portion sizes or snacks between meals. For others, it may be more about changing what they eat than how much. Almost everyone can benefit from eating more plants. Fruits, vegetables, whole grains and legumes tend to be lower in fat and higher in fiber and micronutrients. They are more nutritious and can make you feel fuller and more satisfied after eating fewer calories.
Everyone has heard that diet and exercise are both important to weight loss and weight maintenance. But exercise doesn’t have to mean a gym membership. Just walking at a moderate pace is one of the most efficient types of exercise for weight loss. Just 30 minutes, five days a week is what healthcare providers suggest. A daily walk at lunchtime or before or after work can make a real difference.
Counseling, support groups and methods such as cognitive behavioral therapy may have a role to play in supporting your weight loss journey. These methods can help rewire your brain to support positive changes. They can also help you manage stress and address emotional and psychological factors that may be working against you. Weight and weight loss efforts affect us on many levels, so it can be helpful to have support on the human side as well as on the practical side.
Your healthcare provider may recommend medications to use in conjunction with other treatments. Medications aren’t the whole answer to weight loss, but they can help tackle it from another angle. For example, appetite suppressants can intercept some of the pathways to your brain that affect your hunger. For some people, this might be a small piece of the puzzle, but for others, it might be a bigger one.
Common FDA-approved drugs for treating obesity include:
If you have been diagnosed with class III obesity, bariatric surgery may be an option for you. Surgery is a severe but highly effective solution to long-term, significant weight loss. It works by changing your biology instead of just your mind or your habits. All bariatric surgery procedures alter your digestive system in some way. They restrict the number of calories you can consume and absorb. They also change hormonal factors in your digestive system that affect your metabolism and hunger.
Bariatric surgery procedures include:
Preventing obesity is easier than treating it once it has taken hold. Once your body has established a new high “set point," it will consider that to be your new baseline weight. Your body works to modulate your hunger signals and energy expenditure to maintain the same body mass, in spite of your weight-loss intentions.
If you’ve noticed a pattern of recent weight gain in yourself or your child, or if you have a family history of obesity, you might want to take steps to intervene sooner rather than later. Examining your habits and making reasonable changes now can help you prevent future obesity and weight loss struggles.
Obesity puts you at risk of certain adverse health conditions. That doesn’t mean you have those conditions right now. And it doesn't mean that you can’t do anything about them. The risks are worth your concern, but they’re also reversible or manageable. Your healthcare provider will encourage you to reduce them by losing weight. While it will be challenging, it can be done.
Remember, weight loss of just 5% to 10% can significantly improve your health risks. It can slow or stop the progression of fatty liver disease, metabolic syndrome and diabetes. With medical guidance, weight loss of at least this much is achievable, and possibly much more. Sticking with a long-term treatment plan can help you maintain weight loss.
A note from Cleveland Clinic
You may have experienced a bias that obesity is a personal choice or a moral failure. If you’re seeking medical advice for obesity, chances are you’ve already tried to manage it several times on your own.
The good news is that as research continues, breakthroughs in medicine continue to offer new hope for treating obesity. It might take some exploring to land on the right formula for you, but together with your healthcare provider, you can take your health back into your own hands. Even a little weight loss can improve your health on almost every level, and you can reap lifelong benefits from healthy diet and lifestyle changes.
Last reviewed by a Cleveland Clinic medical professional on 06/13/2022.
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