American women and men weigh on average 8 pounds more than they did in 2000, according to the Centers for Disease Control and Prevention (CDC). Today, over 39 percent of adults in the U.S. are considered obese, and more than 70 percent are overweight, per the CDC.
And that's likely to increase, says Robert Kushner, MD, professor of medicine at Northwestern University Feinberg School of Medicine in Chicago. Culprits include increased caloric intake and reduced physical activity, but Dr. Kushner points to other factors, too, like poor sleep habits and the increased levels of stress we experience in our daily lives.
Overweight vs. Obese
An adult is considered overweight with a body mass index (BMI) between 25 and 29.9, while a BMI of 30 or higher is defined as obese. But Dr. Kushner warns that using BMI as a standalone diagnostic tool is problematic, since it doesn't take into account the distribution of body fat nor the actual health of the individual. For example, additional key health factors, like waist size, might not be reflected in a person's BMI.
Women with a waist size of more than 35 inches and men with a waist size of more than 40 inches may have higher chances of developing diseases related to obesity, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
"A larger waist circumference signifies increased visceral fat (or fat that is located within the abdominal cavity) and predicts the development of multiple medical problems and death rate better than total body fat alone," Dr. Kushner says. A woman who carries extra weight around her waist is more likely to have health problems than a woman who weighs exactly the same but carries her weight around her hips and thighs, he adds.
Obesity's Health Risks
Today, more than 29 million Americans have type 2 diabetes, according to the CDC, making it the seventh-leading cause of death in the U.S. Extra weight sometimes causes insulin resistance, a condition in which liver, muscle and fat cells do not use insulin well. This resistance can, in turn, cause blood glucose levels to rise, leading to diabetes, per the NIDDK.
Interestingly, while obesity in general raises your risk for this condition, the danger isn't divided evenly between the sexes. According to an October 2019 study in PLOS Genetics, which looked at biobank data from more than 400,000 people, women experience a higher risk than men.
According to 2011 research published in the Texas Heart Institute Journal, people at risk for diabetes who lost 7 percent of their body weight through different lifestyle interventions, including 30 minutes of moderate physical activity daily and calorie reduction, were less likely to develop the disease than folks who made no lifestyle changes.
2. Heart Disease
Around 610,000 people die of heart disease in the U.S. every year, according to the CDC, making it the leading cause of death. Frightening? Definitely. There are a number of factors linked to obesity that increase a person's risk for heart disease, including high blood pressure, impaired glucose tolerance, metabolic syndrome and high blood lipids (especially high triglycerides and LDL cholesterol), according to the Cleveland Clinic.
There is more and more research drawing parallels between weight gain and cancer risk. While there are several potential correlations between the two, a common one experts cite is chronic low-level inflammation — or pain, redness, swelling or warmth that occurs as the immune system responds to injury or illness. People with obesity are prone to inflammation, which can lead to DNA damage that may contribute to cancer risk over time, according to the National Cancer Institute.
The list of cancers linked to obesity includes liver, kidney, pancreatic, gallbladder, colorectal and breast, according to the CDC. One study, which was published January 2020 in the Journal of Internal Medicine and looked at more than 300,000 people over a 40-year timespan, found that being overweight or obese is associated with an increased risk of neurological and blood cancers as well. And a June 2019 study in Cancer showed strong evidence tying obesity to aggressive forms of prostate cancer.
What's more, a study published October 2019 in the International Journal of Epidemiology found that being overweight before the age of 40 increases the risks of various cancers in both men and women. The study, which include 220,000 adults, concluded that the risk of endometrial cancer increased by 70 percent, male renal-cell cancer by 58 percent and male colon cancer by 29 percent.
Budding research has also connected obesity to skin cancer. Although this link hasn't been studied quite as much, one nonrandomized controlled trial published January 2020 in JAMA Dermatology found that bariatric surgery lowered the risk of developing malignant melanoma. The researchers concluded, then, that obesity is a risk factor for this type of cancer.
4. The Brain and Mental Health
There are also psychological effects when it comes to obesity. Dr. Kushner says obesity can lead to increased social isolation and low self-esteem. "There is the effect of weight bias and stigmatization, conditions that affect someone for a lifetime," he says. Those stigmas can lead to greater body-image dissatisfaction, overeating, stress, depression and anxiety.
"Being exposed to more frequent stigmatizing experiences has been associated with more negative psychological symptoms and higher body weight," he says. "We all need to be aware of passing comments and glances that we give to people who have obesity — they can have long-term consequences."
Obesity can affect the brain physically, as well. Growing evidence shows that obesity may accelerate or advance the onset of brain aging. A November 2016 study in Neurobiology of Aging found that being overweight was associated with brain changes that correspond to an age increase of about 10 years.
Plus, those with obesity may be more likely to develop dementia. A study published December 2019 in the online issue of Neurology followed more than 1 million women for nearly two decades and found that obesity in midlife was linked to a 21 percent greater risk of dementia later in life. The authors pointed out, though, that the study only looked at women, so the results may not be the same for men.
Read more: What Your Body Shape Says About Your Health
Obesity can damage the bones. In a November 2013 study published in Radiology, researchers found that people with obesity have higher levels of fat in their muscle tissue, blood, liver and bone marrow, putting them at greater risk for osteoporosis.
Being overweight or obese is a major risk factor for stroke, according to the Obesity Action Coalition. One reason may be that obesity increases inflammation in the body caused by excess fat, which can hamper blood flow and up the risk of a blockage. Another is that obesity often comes with high blood pressure, which is the leading cause of stroke.
According to a review published October 2012 in the journal Stroke, central obesity (aka a large waist circumference) is typically a better predictor of stroke than an overall high BMI. Also, the risk for stroke associated with obesity seems to be higher for middle-aged people than older adults.
7. Gallbladder Disease
A higher-than-healthy weight can also put you at risk for developing gallstones (hardened particles that block the release of bile from the gallbladder), which can in turn up your risk for gallbladder disease, per the Mayo Clinic.
Keep in mind that rapid weight loss can also increase your odds of getting gallstones, so it's best to lose weight at a slow-and-steady pace (1 to 2 pounds per week).
8. Sleep Apnea
Obesity also greatly increases your risk of sleep apnea, according to the Mayo Clinic. This sleep disorder is marked by stop-and-start breathing during the night, which can be caused by excess fat around the upper airway that obstructs breathing. For those who are obese, losing weight may help cure sleep apnea.
The Future of Obesity
Now that obesity has been classified as a disease, the understanding of what makes some individuals more susceptible to gaining weight will continue to evolve.
"We know that there are reward centers in the brain that entice increased eating and fat tissue in the abdominal compartment that send out signals to increase metabolic diseases," says Dr. Kushner. "It is a serious medical problem that requires serious treatment. Telling people to eat less and move more will not solve the problem."
But are you genetically destined to be overweight or obese? While there is a strong genetic component to obesity, that doesn't mean you're guaranteed to be overweight or obese, Dr. Kushner says. "The genes determine your vulnerability for being overweight, while the environment and how you live your life affect what you will ultimately weigh."
Is This an Emergency?
- National Cancer Institute: "Obesity and Cancer"
- Cancer: "Body fat distribution on computed tomography imaging and prostate cancer risk and mortality in the AGES‐Reykjavik study"
- Neurobiology of Aging: "Obesity Associated With Increased Brain Age From Midlife"
- Cleveland Clinic: "Obesity & Heart Disease"
- Radiology: "Ectopic and Serum Lipid Levels Are Positively Associated with Bone Marrow Fat in Obesity"
- American Heart Association: "2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults"
- The National Institute of Diabetes and Digestive and Kidney Diseases: "Health Risks of Being Overweight"
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- PLOS Genetics: "Causal relationships between obesity and the leading causes of death in women and men"
- Neurology: "Body mass index, diet, physical inactivity, and the incidence of dementia in 1 million UK women"
- JAMA Dermatology: "Association of Bariatric Surgery With Skin Cancer Incidence in Adults With Obesity"
- Obesity Action Coalition: "Obesity and Stroke Fact Sheet"
- Stroke: "Obesity: A Stubbornly Obvious Target for Stroke Prevention"
- Mayo Clinic: "Cholecystitis"
- Mayo Clinic: "Sleep Apnea"
- Journal of Internal Medicine: "Hospital‐diagnosed overweight and obesity related to cancer risk: a 40‐year Danish cohort study"