Strangely, some people who are overweight seem to be healthier than those who fit standard medical guidelines. Here’s what you should know.
Once in a while, a study will unexpectedly upend decades of medical thought. In the 1990s, bacteria — not stress, as was long thought — were found to be the cause of ulcers. Meanwhile, hormone therapy has proved harmful, rather than helpful, for postmenopausal women.
Another issue researchers may now be reconsidering: weight. For decades, doctors have believed being overweight to be unhealthy in many ways. A flurry of controversial studies has brought that assumption into question.
The conundrum: in some circumstances, people who weigh more seem to fare better than those who fit standard medical guidelines. Nature has called it the “mildly overweight paradox.” In a 2015 study of people with type 2 diabetes, those who weighed the least had the worst outcomes, while those who were overweight, but not obese, were least likely to die from any cause. Another 2014 meta-analysis of outcomes after heart surgery found similar results: those who weighed least had the highest mortality risk, while those who were somewhat overweight again did best.
Part of the confusion may lie in how weight is calculated. Researchers often use body mass index (BMI), but can use other methods as well. A kind of medical shorthand, BMI compares only weight to height. For a person 5 feet 3 inches tall, the BMI “healthy” weight tops out at 130 pounds; for a person 6 feet tall, it’s 180 pounds. A person with significant muscle mass (which is denser than fat), such as a marathon runner, could fall into the “unhealthy” BMI range — despite all other fitness indicators.
Even when they’re considered overweight by medical standards, some people seem to remain metabolically healthy. In one of the studies that ignited significant debate, performed by researchers at the National Institutes of Health, those who were overweight saw a broad overall survival benefit compared to other weights.
“Overweight” in the study corresponded to a BMI between 25 and 30 — a range into which 40 percent of adult men and nearly 30 percent of adult women in the United States fall. First-degree obesity included those with BMIs less than 35. While significant obesity increased mortality in the study, first-degree obesity did not.
The study baffled doctors — one prominent researcher actually called it a “pile of rubbish.” Others have struggled to explain its findings. The authors suggest several reasons for the protective effects of weight, such as extra fat lending cardioprotective benefits or simply providing reserves to combat a stretch of ill health. Genetics also seem significant. Many people follow a healthy diet, even exercise consistently, yet still never lose weight — all without apparent long-term harm.
Some experts point to physical activity as the primary differentiator of metabolic health. A 2013 study looked at fitness in people with obesity (as measured by body fat percentage this time, not BMI). Healthy participants — defined as those with no or only one symptom of metabolic syndrome — were more fit and had a 30 to 50 percent reduced risk of cardiovascular disease, all-cause mortality, and cancer compared to those with more metabolic risk factors.
Researchers have moved quickly to examine the implications of this new research. In a study published in May 2017, researchers used data from the ongoing U.S. National Health and Nutrition Examination Survey to examine whether a new standard called the Fitness Fatness Index — which combines cardiorespiratory fitness measures with waist-to-height ratio — can predict overall health. The results were promising. For every point increase in the index (indicating better health), participants were 11 percent less likely to die of cardiovascular conditions and 9 percent less likely to die from all causes.
The work of basic science will surely continue. Recent research has identified 97 genes related to obesity — including some that seem protective against diabetes and heart disease even in the presence of overweight.
Yet in another study presented at a conference in May 2017, this one of 3.5 million people in the United Kingdom, those defined as obese (a BMI over 30) but metabolically healthy were still at 49 percent higher risk for a range of cardiovascular conditions than those with a BMI in the normal range. The presentation drew media coverage suggesting the “death knell” of the healthy obesity theory. Still, the researchers had not revealed their full dataset at the time of this writing. It’s unclear how those in the simply overweight range (BMI between 25 and 30) — who were healthiest in the NIH study — fared.
No one is suggesting anyone should gain weight, experts agree. Yet some, pointing to a philosophy known as Health at Every Size, propose healthy weight ranges could be broader than has generally been believed.
As described in a book of the same title, participants in a Health at Every Size program reported significant physical and emotional benefits. While they didn’t lose weight, they had higher self-esteem by the end of the program than those on a standard diet, and their metabolic indicators also improved. Meanwhile, half the dieters dropped out — and those remaining eventually regained all the weight they initially lost.
August 14, 2017
Janet O’Dell, RN