Young adults with obesity who lose enough weight to drop down into the “overweight” category by midlife are half as likely to die early as those who stay obese, according to a study published late last week in JAMA Network Open.
The authors of the study also estimate that one in eight early deaths in the United States may be linked to people becoming overweight or obese during early and mid-adulthood.
These findings underscore the urgent need for a “greater emphasis on treating obesity early in life,” the study’s authors conclude. For, as the researchers also point out, very few young adults with obesity — less than 1 percent — are successful at bringing their weight down by midlife.
Obesity is a major — and growing — health issue, both for individuals and for the broader society. It’s been linked to a long list of health problems, including high blood pressure, coronary heart disease, stroke, type 2 diabetes, certain cancers (including breast, colon and kidney), osteoarthritis and clinical depression. Obesity has also been linked to an increased risk of severe illness and death from COVID-19.
Currently, 40 percent of American adults — including young adults aged 20 to 39 — have obesity (defined as a body mass index, or BMI, of 30 to 34.9), and 18 percent have severe obesity (a BMI of 35 or higher). Those figures are expected to rise significantly during the next decade. Within 10 years, one in two American adults will have obesity and one in four will have severe obesity, a study published last year estimated.
Minnesota’s obesity rate is currently 30 percent — a figure that’s predicted to jump to 46 percent by 2030.
Past studies have shown that gaining excess weight during adulthood is associated with an increased risk of early death. It hasn’t been clear, however, if that risk can be significantly lowered if people who had obesity in their 20s or 30s manage to shed the weight later. The current study set out to see if it could help answer that question.
How the study was done
The researchers — a team led by Andrew Stokes, an assistant professor of global health at Boston University — used data collected from 24,205 Americans who took part in the National Health and Nutrition Examination Survey (NHAMES) between the years 1998 and 2015. When they filled out the survey, the participants were between the ages of 40 and 74. Using the survey data, the researchers calculated each participant’s BMI. They did the same for the participants’ BMI 10 years earlier and at age 25, although the data used for those calculations was self-reported by the participants.
The study followed the participants for an average of seven years, during which 5,846 of them died. The researchers then looked to see if the data revealed a relationship between BMI change and the likelihood of death during the study period.
The study found that the lowest risk of death occurred among individuals who had a weight within the “normal” range at age 25 and who maintained a weight within that range as they entered midlife (their 40s). But they also found that people whose BMIs dropped from the “obese” range at age 25 to the “overweight” range by midlife were 54 percent less likely to have died during the study period than those whose BMIs had stayed in the “obese” range.
Interestingly, a similar change in weight (from “obese” to “overweight”) after midlife was not associated with a reduced risk of early death. That finding is probably because “weight loss at an older age is often unintentional, associated with underlying health conditions and/or age-related loss of muscle mass, whereas weight loss earlier in life tends to capture changes in fat mass and is less likely to be affected by the onset of chronic diseases,” the study’s authors explain.
All these findings were calculated after the researchers controlled for other factors known to be associated with early death, such as gender, smoking and educational level.
The researchers also point out that significant drops in weights after the age of 25 were rare. Only 0.8 percent of the participants in the study switched categories from “obese” to “overweight.”
Limitations and implications
The study comes with some important caveats. Most notably, the study is observational, so it can’t prove a direct connection between BMI and early death. It also relied on the participants’ self-reports to calculate their BMIs at earlier ages. Those recollections may not have been accurate. In addition, the study did not adjust for physical activity or diet in early adulthood — or whether the weight loss was intentional or unintentional. Those variables may have influenced the findings. Another limitation is the low number of participants who lost weight between early adulthood and midlife — a factor that, as the researchers acknowledge, limits the precision of the study’s estimates.
Still, the findings are robust enough to be both troubling and hopeful. They are troubling because they suggest having obesity from young adulthood through midlife raises the risk of an early death. Today, four in 10 young adults in the U.S. have obesity. But the findings are hopeful, too, because they suggest that losing much of that excess weight — enough to get down to the “overweight” category — may cut the risk of early death in half.
“At the population level, we estimated that weight loss from obese to overweight would prevent more than 3 percent of premature deaths, and preventing weight gain from normal weight could prevent more than 12% of premature deaths,” the researchers conclude.
“Our findings support the importance of population-based approaches to preventing weight gain across the life course and a need for greater emphasis on treating obesity early in life,” they add.
FMI: The study can be read in full on the JAMA Network Open website.