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.

What are the three types of obesity?

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:

• Class I obesity: BMI 30 to < 35 kg/m².
• Class II obesity: BMI 35 to < 40 kg/m².
• Class III obesity: BMI 40+ kg/m².

What is “morbid” obesity?

“Morbid obesity” is an outdated term for class III obesity.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.

How is childhood obesity assessed?

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.

How common is obesity?

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.

How does obesity affect my body?

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%).

Metabolic changes

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:

• Type 2 diabetes. Obesity specifically raises the risk of Type 2 diabetes seven-fold in people assigned male at birth and 12-fold in people assigned female at birth. The risk increases by 20% for every additional point you gain on the BMI scale. It also diminishes with weight loss

Cardiovascular diseases. High blood pressure, high cholesterol, high blood sugar and inflammation are all risk

• factors for cardiovascular diseases, including coronary artery disease, congestive heart failure, heart attack and stroke. These risks increase hand-in-hand with your BMI. Cardiovascular disease is the leading cause of preventable death worldwide and in the U.S.
• Fatty liver disease. Excess fats circulating in your blood make their way to your liver, which is responsible for filtering your blood. When your liver begins storing excess fat, it can lead to chronic liver inflammation (hepatitis) and long-term liver damage (cirrhosis)..
• Kidney disease. High blood pressure, diabetes and liver disease are among the most common contributors to chronic kidney disease.
• Gallstones. Higher blood cholesterol levels can cause cholesterol to accumulate in your gallbladder, leading to cholesterol gallstones and potential gallbladder diseases.

Direct effects

Excess body fat can crowd the organs of your respiratory system and put stress and strain on your musculoskeletal system. This contributes to:

• Asthma.
• Sleep apnea.
• Obesity hypoventilation syndrome.
• Osteoarthritis.
• Back pain.
• Gout.

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.

Indirect effects

Obesity is also associated indirectly with:

• Memory and cognition, including a heightened risk of Alzheimer’s disease and dementia.
• Female infertility and pregnancy complications.
• Depression and mood disorders.
• Certain cancers, including esophageal, pancreatic, colorectal, breast, uterine and ovarian.

What causes obesity?

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:

• Fast and convenience foods. In communities and families where highly-processed fast and convenience foods are dietary staples, it’s easy to consume a lot of calories. These foods are high in sugar and fat and low in fiber and other nutrients, which can leave you hungrier. Their ingredients promote addictive eating patterns. In some communities, these may be the only types of foods readily available, due to both cost and access. The Centers for Disease Control estimate that 40% of households in America live more than a mile from healthy food retailers.
• Sugar is in everything. The food industry is not designed to maintain our health. It’s designed to sell products that we will become addicted to and want to buy more of. High on that list of products are sweets and sugary drinks, which have no nutritional value and a lot of added calories. But even standard foods have high levels of
• Added sugar to make them more appealing and addictive. It’s so common that it’s changed our taste expectations.
• Marketing and advertising. Pervasive advertising pushes processed foods, sweets and sugary drinks, the products that we need the least but that the industry needs us to buy the most. Advertising makes these products seem like a normal and necessary part of everyday life. Advertising also plays a large role in selling alcoholic drinks, which add a lot of empty calories.
• Psychological factors. Boredom, loneliness, anxiety and depression are all common in modern society, and can all lead to overeating. They may especially lead to eating certain types of foods that activate pleasure centers in our brains, foods that tend to be higher in calories. Eating to feel better is a primal human instinct. We evolved to find food, and evolution hasn’t caught up to the kind of abundance of food that Western societies now enjoy.
• Hormones. Hormones regulate our hunger and satiety signals. Many things can disrupt these regulatory processes, including common things like stress and lack of sleep and less common things like genetic variations. Hormones can cause you to continue to crave more food even when you don’t need any more calories. They can make it hard to tell when you’ve had enough.
• Certain medications. Medications that you take to treat other conditions may contribute to weight gain. Antidepressants, steroids, anti-seizure medications, diabetes medications and beta-blockers are among them.

Factors that may decrease how many calories we spend include:

• Screen culture. As work, shopping and social life continue to move online, we increasingly spend more time in front of our phones and computers. Streaming media and binge-watching make long hours of sedentary entertainment more possible.
• Workforce changes. With industry changes trending toward automation and computers, more people now work at desks than on their feet. They also work longer hours.
• Fatigue. Sedentary lifestyles have a snowball effect. Studies show that the longer you sit still, the wearier and less motivated you become. Sitting makes your body stiff and contributes to aches and pains that discourage movement. It also causes general stress, which adds to fatigue.
• Neighborhood design. Many people lack local places to be active, either due to access or safety issues. More than half of Americans don’t live within half a mile of a park. They may not live in walkable neighborhoods, and they may not see others in their communities being active in day-to-day life. When there is no public transportation option, most people can only travel by car.
• Childcare trends. Children spend less time playing outside than they used to. They spend more time in enclosed childcare environments, which may not have adequate space or facilities for physical activity. This is partly due to cultural trends that don’t find it safe for children to play outside unattended. It’s also due to inadequate access to public spaces and inadequate access to quality childcare. Many childcare environments substitute TV for free play.
• Disability. Adults and children with physical and learning disabilities are most at risk for obesity. Physical limitations and lack of adequate specialized education and resources can contribute.