Obesity is a term that, well, carries a lot of weight, because of varying cultural norms and stigmas about body size and shape. But for the purposes of this overview, we’ll focus on the World Health Organization’s (WHO) definition: abnormal or excessive fat accumulation in the body that presents a risk to your health. (1)
These health risks include all causes of death, along with a host of chronic conditions, according to the Centers for Disease Control and Prevention (CDC). (2)
Worldwide, the prevalence of obesity has tripled since 1975, according to the WHO. (3)
The agency further states that 39 percent of adults age 18 and older were overweight in 2016 (that’s 1.9 billion adults), and 13 percent were obese (more than 650 million). (3)
Jamie Kane, MD, the director of weight management at Northwell Health in Syosset, New York, attributes this trend to changing eating patterns, particularly in the United States, which is the country with the highest obesity rates worldwide, per the CIA World Factbook. “Portion sizes are larger than they were a few decades ago, and on average, Americans eat 20 percent more calories than they did in the 1970s,” Dr. Kane says. (4,5)
And the social and economic consequences of obesity — including $161 billion in excess healthcare costs and $66 billion in lost workplace productivity in the United States, according to a previous study — are having profound effects throughout the country and around the globe. (6)
But obesity is preventable. (3)
Common Questions & Answers
How does obesity affect the body?
Obesity has the potential to affect every aspect of a person’s health. It is associated with high cholesterol, high blood pressure, type 2 diabetes, sleep apnea, heart attack, stroke, osteoarthritis, and some cancers, among other conditions.
How do you prevent obesity?
Policymakers, businesses, and communities must work together to create healthier environments to address obesity. On an individual level: Know your BMI, develop healthy eating habits, and exercise regularly to prevent obesity.
How does obesity affect COVID-19?
Obesity increases the chances that you’ll experience severe illness, become hospitalized, or die if you contract COVID-19. Obesity can also decrease your lung capacity and affect your immune system’s function, which in turn impairs your ability to recover from COVID-19, says the agency.
How does obesity affect fertility?
Having extra weight can affect your ability to conceive a child. Excess weight can disrupt ovulation or prevent fertility treatments such as in vitro fertilization (IVF) from working. Polycystic ovary syndrome (PCOS), a common cause of infertility, often coexists with obesity, too.
How does obesity cause sleep apnea?
Obesity is a major risk factor for obstructive sleep apnea, a disorder in which breathing stops and starts repeatedly during sleep. Obesity may worsen this issue because of fat deposits in tissues of the body’s upper airway. Sleep apnea may affect up to 45 percent of people with obesity.
Obesity and BMI Levels Explained
Obesity is generally assessed using body mass index, or BMI, according to the CDC. (7)
BMI takes both a person’s height and weight into account and is expressed in units of kilograms per square meter (kg/m2).
BMI levels for adults are categorized as follows:
Normal weight: 18.5 to 24.9
Overweight: 25 to 29.9
Obese: 30 or greater
Obesity is further classified as:
Class 1 obesity: BMI = 30 to 34.9
Class 2 obesity: BMI = 35 to 39.9
Class 3 obesity: BMI 40 or higher
The health risks associated with BMI may vary somewhat according to ethnicity, notes the Joslin Diabetes Center at Harvard University in Boston. They state, “Asians and Asian Americans may have increased health risks at a lower BMI.” Joslin has created a BMI calculator for this population that lowers the floor for overweight BMI to 23 and the floor for obesity to 27. (8)
An article published by the Harvard T.H. Chan School of Public Health notes some studies have found that Black people have lower body fat and higher lean muscle mass than whites at the same BMI; meaning that at the same BMI, they may have a lower risk of developing obesity-related diseases. (9)
BMI is a good starting point as a screening tool, says Mir Ali, MD, a bariatric surgeon and the medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, California. But because it takes into account only height and weight, and not muscle composition or other factors, BMI is an imperfect measurement.
Learn More About Obesity and BMI Levels
Some health organizations also refer to people with an extreme amount of excess weight as “morbidly obese,” and the U.S. National Library of Medicine’s MedlinePlus guide defines people who are 100 pounds (lb) (45 kg) or more over their ideal weight as being in that category. (10)
But this term is highly stigmatizing, as is the word “fat,” point out the authors of an article published in the Journal for Nurse Practitioners. Terms such as “unhealthy weight” or “high BMI” are more appropriate and motivating to people who carry excess weight, they advise. (11)
In addition to interfering with quality of life, having class 2 or 3 obesity (a BMI of 35 or greater) can take nearly four years off your life compared with being at a normal weight, according to a study published in the American Journal of Public Health. (12)
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There are many online tools that will calculate your BMI.
Adults can use a BMI calculator to determine their BMI.
Children should use a different BMI calculator than adults because their BMI is determined using a percentile system. The CDC provides a BMI calculator for children ages 2 through 19. (13)
As mentioned, the Joslin Diabetes Center created a BMI calculator for Asian people, and this resource lowers the beginning point for overweight BMI to 23 and the beginning point for obesity to 27. (8)
Learn More About BMI Calculators
Obesity in Children
The World Health Organization calls childhood obesity “one of the most serious public health challenges of the 21st century.” (14)
Obesity not only lowers a child’s quality of life during childhood but increases the chance that the excess weight will persist into adulthood, says the pediatric endocrinologist Sheila Perez-Colon, MD, who practices at Kidz Medical Services in Miami and Hialeah, Florida. It also raises the risk a child will develop obesity-related diseases such as type 2 diabetes, heart disease high cholesterol, high blood pressure, stroke, and certain types of cancer at a younger age or as an adult. “It could even lead to anxiety and depression,” she adds.
More than 340 million youths worldwide ages 5 to 19 were overweight or obese in 2016, and 38 million children under age 5 were overweight or obese in 2017. (14)
The CDC reports that in the United States, obesity affected 18.5 percent of youth age 2 to 19 in 2016, and was more prevalent in Hispanic (25.8 percent) and non-Hispanic Black children (22 percent) than in non-Hispanic white children (14.1 percent). (15)
Parents of children who are becoming obese may not recognize the warning signs, particularly if they are overweight themselves, says Dr. Perez-Colon. “You see, visually, an increasing weight overall on the patient or you see rapid weight gain. You will see what we call central obesity, which is when fat accumulates around the abdominal area. You also may see symptoms of complications such as diabetes; for example, increasing urination. That will give you a red flag saying, Hmm, something may be wrong here.”
Perez-Colon says lifestyle habits that increase a child’s risk for obesity include drinking sweetened beverages such as juice and soda, not eating enough fruits and vegetables, eating late at night, eating large portions, or frequently having seconds. Furthermore, she cautions against children not getting enough exercise and having too much screen time on phones, computers, or TV. “They are not moving. They’re sitting there for a long time.”
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The CDC has tips to help children maintain a healthy weight.
While preventing obesity in children usually comes down to lifestyle changes, Perez-Colon says in rare cases a syndrome with a genetic component or another disease may be to blame, particularly if the weight gain begins when the child is younger than 5.
For instance, if a child’s mother had gestational diabetes, the child is at greater risk for being born at a high birth weight, being obese in childhood and developing type 2 diabetes in adulthood, according to the American Diabetes Association (ADA). (16)
Learn More About Childhood Obesity
Obesity Causes and Risk Factors
The following conditions and factors can put you at higher risk of obesity, according to the CDC. (17,18)
Behavior Not getting regular physical activity and having unhealthy eating habits can contribute to obesity risk.
Community environment Living under conditions that do not enable and encourage safe movement and access to healthy food can increase a person’s chances of developing obesity. Childhood adversity such as maltreatment is also associated with a higher risk for obesity, as a study published in January 2019 in Translational Psychiatry notes. (19)
Genetics Family history, which involves a complex mix of inherited predispositions and environmental factors, and “monogenic” disorders that can be traced back to a single gene mutation, can affect obesity risk.
Other diseases Cushing’s syndrome, depression, and polycystic ovary syndrome (PCOS) are among the disorders that are associated with obesity.
Drugs Some medications can cause weight gain, such as steroids and certain antidepressants.
Race and ethnicity Being Black or Hispanic puts you at higher risk for obesity than if you are white or Asian.
Socioeconomic status People who don’t have a college degree have a higher risk of obesity than people who do. Among men, middle-income status puts you at higher risk for obesity; among women, middle or lower income puts you at higher risk.
Learn More About Obesity Causes
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Obesity Rising Among Adults, Is Stagnant Among Youth: Article
Obesity Rising Among Adults, Is Stagnant Among Youth: Article
While more adults were obese in 2015–2016 than in 2007–2008, the increase in youths affected by obesity between those time frames was not statistically significant, researchers report.Learn More
How Are Genes Related to Obesity?
Obesity runs in families. Having one obese parent gives you a 50 percent chance of being obese, and if both your parents are obese your chance increases to 80 percent, according to an article in the Journal of Clinical Research in Pediatric Endocrinology. (20)
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But, as mentioned, the reasons for this are complex and involve both inherited predispositions and a shared environment. “Only a very small number of people suffer from known genetic disorders causing severe obesity,” explains Kane. Such monogenic disorders can be pinpointed to a single gene variant through testing. MCR4 (melanocortin 4 receptor) gene mutations are the most common among them, he says. The CDC explains that MCR4 changes affect hunger in children and cause a tendency to overeat.
Perez-Colon says genes related to leptin (LEP), a hormone produced by fat cells, and leptin receptor (LEPR), which affects appetite, are also sometimes tested for. She recommends genetic counseling for families who have a history of such mutations. (21)
How Is Obesity Diagnosed?
A common screening tool for obesity in adults is BMI, but in children, growth charts are also consulted and comparisons made with other children their age using a percentile scale, says Perez-Colon.
As Dr. Ali explains, a doctor may also take other factors into account before making a final diagnosis, such as muscle composition.
Prognosis of Obesity
Being merely overweight (a BMI of 25.0–25.9) will not necessarily take years off your life, but having class 2 or 3 obesity (a BMI of 35 or greater) can shave off nearly four years compared with being at a normal weight. (11)
Plus, obesity sets you up for health complications including high blood pressure, high cholesterol, type 2 diabetes, heart disease, stroke, gallbladder disease, osteoarthritis, sleep apnea, and serious COVID-19 disease. (2)
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Duration of Obesity
Obesity does not have to be a permanent condition, says Perez-Colon. “Set your mind to saying, ‘No, I can change it. Even though I’m obese right now, I know that by changing things like my diet and eating more fruits and moving my body more and more exercise, at some point I should be seeing good results.”
You may not see weight loss right away. “But you may see, for example, your blood pressure is improving, or when you go to the doctor, your cholesterol level is improving. That’s definitely a good sign saying that you’re going in the right direction.”
Realistic Weight Loss Goals
If you’re trying to lose weight, you’re in good company. Just shy of half of U.S adults have tried to lose weight within the past year, the National Health and Nutrition Examination Survey indicates. People who lose weight gradually and steadily — at around one to two pounds per week — are more successful at keeping the weight off in the long run than those who try to lose weight quickly, the CDC points out. (22)
Keeping the weight off is a challenge. A previous study found that about one in six adults in the United States who has ever been overweight or obese has been able to lose and keep off at least a 10 percent weight loss (a median of 34 lb) for a year or more. (23)
Jamie Gold took three years to accomplish her 100 lb weight loss, and at age 59, she has kept most of it off over the past nine years. Her current BMI is 23.5 — within normal range — and while she does not know what her BMI was to start with, a typical woman of her height and former weight would have had a class 2 obesity BMI of 37.
“I was a 48-year-old, 233 lb couch potato, bingeing on TV shows and junk food in Tampa, Florida, when my marriage fell apart,” explains Gold, who now is a Mayo Clinic certified wellness coach based in San Diego. Fearing that the stress of the divorce, combined with her weight, might put her at risk of a heart attack or stroke, Gold decided to focus on her health. “My first move was to start swimming laps again, as I had during my thirties. It felt great, and I naturally started craving healthier foods again to power my swims. Over the next few years, I added hiking, power walking, and strength training to my fitness plans and greatly reduced carbohydrates.”
Gold struggled at first to maintain the weight loss, until she settled into a training and eating routine for her new passion — running races.
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“I’ve embarked on ever more challenging pursuits — including two marathons, six obstacle course races, a triathlon, and summiting the highest peak in the lower 48 states,” she says, and the challenges keep her motivated to stick to a healthy regimen.
These days she eats a mostly high-protein, low-carb diet without bread, pasta, rice, cereals and other grains. Her protein sources are typically grilled chicken and fish. “One meal a week — usually after a long Sunday hike — is whatever I want to indulge in.
“Like most people, I’ve had [weight] ups and downs since then, but we’re talking 10 to 25 pounds, not 50 or 100! I’ve been maintaining a healthy weight for the last few years,” says Gold.
Obesity Treatment Options
If you are currently managing obesity, have hope. There are ways you can reduce your BMI, reach a healthy weight, and obtain a better quality of life.
Diet and Lifestyle Changes
Gold’s combination of eating a healthier diet and exercising more mirrors the approach to obesity that healthcare providers recommend first. “We always encourage patients to try to diet and exercise first because that is the most safe method for weight loss,” says Ali. Be sure to speak with your doctor before embarking on any diet or exercise plan, to ensure you are making changes that are safe and appropriate for you.
There are a variety of diets that will allow you to lose and maintain weight loss, but the federal 2015–2020 Dietary Guidelines for Americans say that whichever you choose should do the following, whether you are trying to lose or maintain weight: ( 24)
Emphasize fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products, unless you are vegetarian.
Include lean meats, poultry, fish, beans, eggs, and nuts and seeds (with a greater emphasis on beans and peas, soy products, nuts, and seeds if you are vegetarian).
Minimize your intake of saturated fats, trans fats, cholesterol, sodium, and added sugar.
Derive less than 10 percent of calories per day from added sugars.
Derive less than 10 percent of calories per day from saturated fats.
Stay within your daily calorie needs.
Calorie needs vary according to age, gender, activity level, and whether you are trying to lose pounds or simply be at a healthy weight. For adult women the recommended range is 1,600 to 2,400 calories per day and for adult men the range is 2,000 to 3,000 calories per day. For children and adolescents the range is 1,000 to 3,200. The dietary guidelines include a chart where you can find the calorie target that suits you best.
Gold, who is the author of Wellness by Design: A Room-by-Room Guide to Optimizing Your Home for Health, Fitness, and Happiness, says keeping her kitchen organized supports her commitment to healthy eating. “I have my kitchen organized so that the tools I need — including utensils, measuring cups, and food scale — are close at hand.” Her pantry and refrigerator are also organized in a way that makes grabbing healthy ingredients quick. “Last, but not least, is having an anti-fatigue mat that reduces stress on my joints if I’m spending a long time on my feet in the kitchen. If healthy meal prep is painless and easy, it’s more enjoyable and encourages healthy eating.”
According to federal physical activity guidelines for Americans, you should aim for the following level of physical activity, even if you are not trying to lose weight. (25)
At least 150 minutes to 300 minutes a week of moderate-intensity exercise (like walking briskly, line dancing, yoga, playing doubles tennis or raking leaves)
Or 75 minutes to 150 minutes a week of vigorous-intensity aerobic physical activity, such as jogging, running, cycling more than 10 miles an hour, or high-intensity interval training (HIIT)
Older adults with chronic conditions should do as much activity as their health allows.
Preschool-age children should remain active throughout the day and be encouraged to play or otherwise move their bodies.
Children ages 6–7 should do an hour or more of moderate to vigorous physical activity daily.
“In the National Weight Control Registry over 90 percent of those who maintained long-term weight loss engaged in at least 60 minutes per day of physical activity,” Kane notes. (26)
Meanwhile, if you are at the beginning of your weight loss journey and have a lot of weight to lose, be patient with yourself, he advises. Patients with obesity beginning an exercise program must think of the long term. In the end they will want to be engaged in regular physical activity, but it takes time to build up strength, endurance, and flexibility. Be persistent, but safe.”
If diet and exercise alone aren’t enough to get you to a healthy weight, and your BMI is 30 or more (or your BMI is 27–29.9 and you have a complication such as type 2 diabetes or high blood pressure), your doctor may prescribe medication to add to your regimen, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). (27)
Among the more common medications listed by the NIDDK that are FDA-approved for long-term use are: (25)
Xenical (orlistat), which is available at a lower dose without a prescription under the name Alli
Saxenda (liraglutide), an injectable that is also FDA approved at a lower dose to treat type 2 diabetes under the name Victoza
Perez-Colon notes that of these, only orlistat is FDA-approved for children, and only for those age 12 and older. (27)
She says that the type 2 diabetes medication Glucophage (metformin) is sometimes prescribed for weight loss in adults and adolescents as well, but it is not FDA approved for that use. A December 2018 review of studies in Drugs that followed overweight or obese people who were given metformin found that adults experienced a small amount of weight loss over time. (28)
“Obesity medications at higher doses can cause more rapid weight loss, but one typically sees weight regain without continuing them indefinitely,” Kane cautions.
Mental Health Options for Behavioral Change
Research indicates that there’s two-way relationship between obesity and mental health. A previous analysis of studies determined that obesity increases the risk of depression, especially among Americans; and also that depression is a risk factor for developing obesity. (29)
In fact, the CDC reports that 43 percent of adults with depression were obese compared with 33 percent of adults without depression, as of 2010. This greater risk of obesity was especially strong in white women. Rates of obesity by depression status did not differ among men across groups, nor did they differ in Black and Mexican American women and men. (30)
Gold, who is white, concurs about the two-way relationship between obesity and depression. “I think being depressed contributed to my obesity and being obese contributed to my depression. Those feed on each other. Being sedentary added to both, as well.” She says exercise has been a great mood-lifter, especially outdoors. “Getting fit during and after my divorce was also powerful for starting a new phase of my life. I learned that I could do far more than I ever imagined — physically and mentally — and that’s a huge confidence booster for life in general.”
Dominick Gadaleta, MD, a bariatric surgeon in Bay Shore, New York, acknowledges the role that stigma against obesity may play in depression and other mental health problems, in some communities more than others. “The good news is that weight loss efforts, with the help of a mental health professional, can help one cope and develop strategies to reverse or at least diminish the negative feelings.”
If you are seeking professional counseling related to your weight or your perception of it, speak with your doctor for a referral, or do a key phrase search for “obesity/weight-loss” in the American Psychological Association’s Psychologist Locator to find a therapist in your area.
For severely obese patients who have not been able to lose the weight they need to through diet, exercise, and medication, weight loss surgery may be an option. Ali says that patients who come to him for surgery are typically 100 lb overweight.
The American Society for Metabolic and Bariatric Surgery (ASMBS) says other qualifications for bariatric surgery include having a BMI of 40 or greater (even if you are less than 100 lb overweight); or having a BMI of 35–39.39 along with obesity-related complications such as type 2 diabetes, high blood pressure, heart disease, osteoarthritis, nonalcoholic fatty liver disease, sleep apnea or other breathing problems. (31) Candidates usually undergo thorough psychological counseling and a medically supervised diet before surgery, according to the organization. ( 32)
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Weight loss surgery leaves a patient with a stomach that can hold far less food than before, and most options also restrict the body’s ability to absorb calories and nutrients. The procedures are typically minimally invasive laparoscopic surgeries, according to the ASMBS. (33)
Ali says the most common surgery types are:
Roux-en-Y Gastric Bypass (Gastric Bypass)
As the ASMBS explains, in this procedure, the stomach is divided into two sections by a surgeon and only one small part of it holds the food you eat. The lower part of the small intestine is attached directly to that small stomach pouch, so that food can bypass most of the stomach and the upper part of the small intestine. As a result, the body absorbs fewer calories. Then the bypassed section is connected further down to the lower part of the small intestine — still attached to the main part of your stomach — so digestive juices can move from your stomach and the first part of your small intestine into the lower part of your small intestine.
Rerouting the food stream alters gut hormones that suppress hunger, make you feel full when you eat, and reduce high blood glucose (sugar). People lose on average 60 to 80 percent of their excess weight, and maintain a loss of at least 50 percent in the long term, according to ASMBS. (32)
Laparoscopic Sleeve Gastrectomy (Sleeve)
About 80 percent of the stomach is surgically removed from the body, leaving a banana-shaped pouch, as the ASMBS describes it. The amount of food that can be consumed is drastically reduced by the procedure, and changes happen in gut hormones that suppress hunger, make you feel full when you eat, and reduce high blood sugar. People lose around half of their excess weight on average within the three- to five-year timeframe, and maintain that level of loss in the long term, according to the association.
Other less common bariatric surgeries include biliopancreatic diversion with duodenal switch (BPD/DS) gastric bypass and laparoscopic adjustable gastric band (lap band), says Ali. The ASMBS describes how they work. (32)
Intragastric Balloon Therapy (IGB)
For people who have a BMI of 30–39.9, with or without other chronic health conditions, this less-invasive procedure is an option. According to the FDA, a surgeon places one or more inflatable balloons into the stomach endoscopically or through a capsule that is attached to a catheter and swallowed. The balloons are then filled with gas or saline and then sealed to take up space in the stomach and delay the exit of food from the stomach into the small intestine. The balloons are removed at a later date. (34) According to the Mayo Clinic, typical weight loss is about 7–15 percent of your body weight during the six months after balloon placement, and total excess weight loss is in the 30 to 47 percent range. (35)
After the surgery, people must stick to a high-protein, very low carbohydrate diet with small portions per meal, says Ali. The regimen helps to prevent dumping syndrome, in which overly rapid movement of food into the small intestine can cause abdominal cramping, nausea, vomiting, and low blood sugar, the Cleveland Clinic explains. (36)
“As long as you are getting the amount of calories your body needs each day and not eating in excess of that, then you can maintain the weight loss,” says Ali.
Learn More About Weight Loss Surgery
Alternative and Complementary Therapies
A growing area of obesity treatment research revolves around the microorganisms that live in your gut, known as the gut microbiome. These microorganisms — bacteria, fungi, viruses, parasites — perform a variety of routine functions in symbiosis with your body’s own cells and tissues, the Harvard T.H. Chan School of Public Health explains. (37)
“Alterations to the composition and diversity of the microorganisms that make up the gut microbiome have been linked to a number of conditions and diagnoses — including obesity,” says Daniel Ramon Calvo, PhD, the director of Biopolis, a microbial biotech company subsidiary of Archer Daniels Midland (ADM).
“Specifically, reductions in certain species or overall reductions in microbial diversity have been associated with increased rates of obesity, as well as type 2 diabetes and dyslipidemia [high cholesterol],” says Dr. Calvo, who coauthored a small randomized controlled double-blind clinical trial on a probiotic strain of bacteria called Bifidobacterium lactis (BPL1) along with other researchers at ADM.
Study participants who swallowed a daily capsule of heat-killed BPL1 “showed a significant reduction in waist circumference after 12 weeks of treatment — 64 percent of [participants taking] BPL1 achieved faster, comparable reduction in waist circumference than with 6 to 12 months of multifactorial lifestyle interventions.” Furthermore, 56 percent of individuals taking BPL1 showed a reduction in visceral fat. Participants who took live BPL1 showed a statistically significant reduction in BMI, says Calvo.
But a March 2018 review in the International Journal of Obesity of human studies and clinical trials relating to the gut microbiome and obesity found that results have been inconsistent, and that more research and better management of gene sequencing data are needed. (38)