“The U.S. obesity epidemic is not slowing down,” says lead author Larry Tucker, PhD, professor in exercise sciences at Brigham Young University in Provo, Utah. “These results leave no doubt that 10-year weight gain is a serious problem within the U.S. adult population,” he says. That’s because long-term weight gain drives overweight and obesity, and obesity is replacing smoking as the most serious preventable cause of premature death and disease in America, says Dr. Tucker.
Overweight and Obesity Associated With Nearly 1 in 5 U.S. Deaths
Obesity is a growing health crisis, both in the United States and around the world. It’s estimated that nearly 1 in 5 deaths in the United States — 18.2 percent — are associated with overweight and obesity. From 1999–2000 through 2017–2018, obesity prevalence in the United States has increased from 30.5 percent to 42.4 percent. A person with a body mass index (BMI) from 25 to 29.9 is considered overweight, and a person with a BMI of over 30 is considered to be obese. BMI is calculated based on a person’s weight and height and the same formula is used for both men and women. No one thing causes obesity; it’s a combination of causes and individual factors including dietary patterns, genetics, physical activity, inactivity, and medication use. Study participants were selected randomly from all regions and races across the country as part of the annual National Health and Nutrition Examination Survey (NHANES). NHANES is a Centers for Disease Control and Prevention (CDC)–sponsored series of studies that began in the early 1960s and became a continuous program in 1999. A total of 13,802 adults were included in the study. Participants reported how much they weighed 10 years prior and their current body weight was measured.
Over Half of People Gained 5 Percent of Their Body Weight in a Decade
Researchers found that about 1 in 2 people — 51 percent — gained 5 percent or more of their body weight. Five percent is the official cut-point for clinically significant weight gain, explains Tucker. “With 5 percent weight gain, blood pressure increases, LDL cholesterol increases, HDL cholesterol decreases, type 2 diabetes increases, heart disease increases, physical activity decreases, and dozens of other health problems manifest themselves,” he says. More than 1 in 3 people gained 10 percent or more body weight, and almost one-fifth gained 20 percent or more body weight over the 10 year time period. Although the study wasn’t designed to uncover why people did or didn’t gain weight, the authors cited findings from existing research to suggest possible reasons about why some groups were more likely to add extra pounds than others.
Why Are Younger People Gaining More Weight Than Older People?
Although the prevalence of obesity increases with age, weight gain is actually greatest across the younger years of adult life — late twenties and thirties — and diminishes gradually over time as adults get older, says Tucker. This seems to go against national obesity findings that indicate the prevalence of obesity increases with age, but there could be a few reasons behind this trend. For starters, it takes time for body weight to accumulate. The initial weight gain of roughly 17 pounds that the average person in their twenties gains often isn’t enough to push most people into the obese category, but if an adult adds the average number of pounds gained during each decade of adult life, that equals over 45 pounds. In many cases, that would be enough to put many people into the obese category. Another reason could be that metabolism increases with weight gain, and so larger adults have higher metabolisms than smaller adults. The authors write, “Just as it takes more fuel to maintain a larger house than a smaller one, individuals with obesity require more fuel to maintain their weight than non-obese individuals.” That means as body weight increases, it takes an increasing number of calories to cause more weight gain, and so weight gain tends to slow with each decade of age in the average adult, the authors noted.
Women Gain About Twice as Much Weight as Men Over 10-Year Period
The study also found that 10-year weight gain was significantly greater in women than in men, with women gaining about twice as much weight: 12 pounds on average for women, compared with 6 pounds for men. This disparity doesn’t appear to be a worldwide trend — one study in Norway found that men gained more weight than women over a 10-year period, and one in Australia found no difference in weight gain between men and women. The difference in weight gain between the sexes in the United States is often chalked up to childbirth. A 2019 study of 2,459 women published in BMJ Open found that women gained an average of 3 to 5 pounds per child. “Weight gain during pregnancy takes significant effort to lose and if the weight is not lost, overweight and obesity develop over time,” says Tucker. There’s also evidence to suggest that women tend to be less physically active than men, which could also account for some of the weight gain differences, the authors wrote.
Weight Gain Differed According to Race and Ethnicity
Weight gain also differed across races, with Black women experiencing the greatest average weight gain over the 10-year period — 19.4 pounds. This could be due to a combination of factors, including education and income disparities, which have been shown to influence the risk of having overweight or obesity, according to the authors. There is also evidence to suggest a connection between food insecurity and obesity, particularly in Black and Hispanic women.
Findings Can Help Healthcare Providers Focus Prevention Efforts
“The findings of this study will inform healthcare professionals and educators of the individuals who are most at risk of weight gain and when that weight gain tends to occur in the U.S.,” says Tucker. That knowledge can be used to focus prevention efforts, he adds.
