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 considered overweight, according to the CDC.
And that's likely to increase, says Robert Kushner, MD, professor of medicine at Northwestern University Feinberg School of Medicine in Chicago, due to increased caloric intake and reduced physical activity, sure, but also other factors. "Medications ... could have the unintentional consequence of weight gain, poor sleep habits and increased stress of daily life" also contribute to America's growing waist circumference, he says.
Overweight Versus Obese
An adult is considered overweight with a body mass index (BMI) between 25.0 and 29.9; a BMI of 30 or higher is defined as obese. But Dr. Kushner warns that using BMI as a stand-alone 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 cardiovascular risk 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 Effect on Health
The list of health consequences of obesity is likely longer than your overwhelming to-do list on a Monday morning. Not only does obesity raise the risk of cardiovascular disease (CVD), but it also puts individuals at greater risk for type 2 diabetes, coronary heart disease (CHD), stroke, gallbladder disease, some cancers, sleep apnea and respiratory problems, according to the American Heart Association.
Additionally, 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.
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.
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 disease, according to the CDC. 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.
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.
Read more: What Your Body Shape Says About Your Health
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"
- Centers for Disease Control and Prevention: "Obesity and Overweight"
- National Health Statistics Report: "Mean Body Weight, Height, Waist Circumference, and Body Mass Index Among Adults: United States, 1999–2000 Through 2015–2016"
- International Journal of Epidemiology: "BMI and weight changes and risk of obesity-related cancers: a pooled European cohort study"
- PLOS Genetics: "Causal relationships between obesity and the leading causes of death in women and men"