About 42 percent of American adults had obesity in 2017 through early 2020, according to the CDC, and more than 9 percent had severe obesity. Among adults with obesity, 58 percent had high blood pressure and about 23 percent had diabetes. For children, almost 1 in 5 kids and teens aged 2 to 19 had obesity in the same period, about 14.7 million young people.
Three questions come up over and over. Does extra weight really shorten your life? If obesity runs in your family, can you do anything about it? And does a heavy child become a heavy adult? Researchers have good answers to all three.
Does extra weight shorten your life?
This one caused a real fight. In 2013 a CDC researcher named Katherine Flegal published a review in JAMA of 97 studies covering more than 2.88 million people. Compared with people at a normal weight, people with obesity overall had a higher risk of dying, and people with a body mass index of 35 or more had about 29 percent higher risk. But people who were overweight, with a BMI of 25 to 30, had a slightly lower risk, and people with mild obesity were about even.
That finding got a lot of headlines. Critics pointed out a problem with studies like these. Smokers and people who are already sick tend to be thinner, and they also die sooner, which can make being thin look riskier than it is.
In 2016 a huge international group tried to fix that. The Global BMI Mortality Collaboration pooled 239 studies with more than 10 million people. For the main analysis they only kept people who had never smoked and had no chronic disease at the start, and they skipped the first five years of follow-up. That left almost 4 million people.
In that cleaner group, the risk of dying was lowest at a BMI of 20 to 25. It went up throughout the overweight range, 7 percent higher at a BMI of 25 to 27.5 and 20 percent higher at 27.5 to 30. At a BMI of 30 to 35 the risk was 45 percent higher. At 35 to 40 it nearly doubled, and at 40 or more it was about 2.8 times higher. The link was stronger in younger people than in older people, and stronger in men than in women. The study was published in The Lancet.
So yes, obesity is a real health risk, and the risk starts to climb before a person reaches the obesity range.
Can exercise beat your genes?
Some people gain weight more easily than others, and genes are part of the reason. The best-known obesity gene is called FTO. Carrying the risky version raises the odds of obesity, and people with two copies weigh more on average.
In 2008 researchers at the University of Maryland studied the gene in 704 Old Order Amish adults in Pennsylvania. The Amish were a good group to study because many of them do hard physical work every day, and the researchers measured their activity with a device instead of asking. The FTO variant was linked to higher BMI only in the people with below-average activity. In the most active people it had no effect on weight at all. The lead author, Dr. Evadnie Rampersaud, was interviewed about the study on the podcast this site started as. The paper was published in the Archives of Internal Medicine.
A much larger follow-up in 2011 pooled 45 studies with more than 218,000 adults. Being physically active cut the effect of the FTO gene on obesity risk by about 27 percent. The same pattern didn’t show up in the studies of children and teens. That study was published in PLOS Medicine.
People with a family history of obesity have even more reason to stay active, not less.
Does a heavy child become a heavy adult?
Often, yes. A 2016 review of 15 long-term studies with about 200,000 people found that children and teens with obesity were about five times more likely to have obesity as adults. Around 55 percent of children with obesity still had it as teenagers, and around 80 percent of teens with obesity still had it as adults.
The same review found something that’s easy to miss. About 70 percent of adults with obesity did not have obesity as children or teens. Most adult obesity starts in adulthood, so focusing only on heavy kids won’t solve the problem.
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What helps
For adults, the research in the other articles in this series points the same way. Diets with very different mixes of fat and carbs lose about the same weight when calories drop, and exercise helps keep it off. The federal Physical Activity Guidelines recommend at least 150 minutes a week of moderate activity plus strength training twice a week, and more activity helps with weight control.
For kids, the guidelines call for 60 minutes or more of activity every day for children and teens aged 6 to 17. Active play counts. Kids tend to copy their parents, so it helps when the whole family walks, bikes or plays together instead of sending a kid outside alone.
If you’re starting from very little, the easy exercises for seniors are gentle enough for most beginners, and the home gym ideas page has ways to work out without a gym membership.
What the research can’t tell you
BMI is a rough measure. It doesn’t separate muscle from fat, so a muscular athlete can land in the overweight range. Most of the studies here are observational and show links, not proof. The gene studies look at one gene, and dozens of others play smaller roles. And none of this is a reason for blame. Weight is shaped by genes, income, sleep, stress, medications and the food around you, not only by willpower.
Talk to your doctor about your weight, especially if you have high blood pressure, diabetes or joint pain.
Where to get help
Your doctor, or your child’s doctor, is the best first stop for questions about weight, since they can check blood pressure, blood sugar and growth and look for medical causes. A registered dietitian can help a whole family change how it eats without making a child feel singled out.
- HealthyChildren.org (American Academy of Pediatrics): obesity, advice for parents on weight, food and activity, written by pediatricians.
- NIDDK: weight management, plain-language guides from the National Institute of Diabetes and Digestive and Kidney Diseases on healthy eating, activity and weight.
- Academy of Nutrition and Dietetics: Find a Nutrition Expert, to find a registered dietitian near you, in person or by video.
Where this page came from
Fitness Rocks started as a podcast by the doctor I bought the site from. In 2008 and 2009 he asked whether obesity is really a health risk, interviewed Dr. Evadnie Rampersaud about obesity genes and physical activity, and covered why childhood obesity is a big deal. Those episodes are gone, so this page brings those questions up to date.
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