Study provides insight into how excess weight is linked to increased risk of death

The findings, published February 9 in the journal Population Studies, counter the prevailing wisdom that excess weight increases mortality only in extreme cases.

The statistical analysis of nearly 18,000 people also highlights the pitfalls of using body mass index (BMI) to study health outcomes, providing evidence that the go-to metric can potentially bias conclusions. With those biases in mind, it’s estimated that 1 in 6 American deaths is related to being overweight or obese.

“Existing studies underestimate the mortality consequences of living in a country where cheap, unhealthy food has become increasingly accessible and sedentary lifestyles have become the norm,” said study author Ryan Masters, associate professor of sociology at CU Boulder. ”

“This study and others are beginning to uncover the true toll of this public health crisis.”

Challenging the Paradox of Obesity

While many studies show that heart disease, high blood pressure and diabetes (which are often associated with being overweight) increase the risk of mortality, very few have shown that mortality is higher in groups with a higher BMI. .

Instead, in what some call the “obesity paradox,” most studies show a U-shaped curve: the “overweight” category (BMI 25–30) surprisingly has the lowest mortality rates. Those in the “obese” range (30-35) have little or no risk over the so-called “healthy” range (18.5-25). And both “underweight” (under 18.5) and extremely obese (35 and over) have an increased risk of death.

“The conventional wisdom is that elevated BMI generally doesn’t increase mortality risk until you reach very high levels, and that there are actually some survival benefits to being overweight,” Masters. said, a social demographer who has spent his career studying mortality. “I am skeptical of these claims.”

He noted that BMI, which doctors and scientists often use as a measurement of health, is based only on weight and height and does not account for differences in body composition or how long a person has been overweight.

“It’s a reflection of stature at a time,” Masters said. category of “obese”. “It’s not fully capturing all the nuances and different sizes and shapes of bodies.”

To see what happened when those nuances were considered, Masters mined the National Health and Nutrition Examination Survey (NHANES), which looked at data from 17,784 people, including 4,468 deaths, from 1988 to 2015.

They found that a full 20% of the sample described as a “healthy” weight a decade earlier were in the overweight or obese category. When isolated, this group had a significantly worse health profile than the same category of people whose weight was stable.

Masters pointed out that carrying excess weight throughout life can lead to diseases, which paradoxically lead to rapid weight loss. If BMI data is captured during this time, it may skew the results of the study.

“I would argue that we are artificially increasing the risk of mortality in the low-BMI category by including people who have a high BMI and have recently lost weight,” he said.

Meanwhile, 37% of those with an overweight and obese BMI of 60% had a low BMI in the prior decade. Notably, those who had recently gained weight had a better health profile.

“The health and mortality consequences of high BMI are not like a light switch,” Masters said. “An expanding body of work is suggesting that the results are duration-dependent.”

By including people who have spent most of their lives in the higher BMI categories with lower BMI weights, previous studies inadvertently made higher BMIs less risky, he said.

When they looked at differences in fat distribution within BMI categories, they also found that the variations made a huge difference in reported health outcomes.

uncover a public health problem

Collectively, the findings confirm that the studies have been “significantly affected” by biases related to BMI.

Crunching the numbers again without these biases, they found not a U-shape but a straight upward line, with the lowest mortality risk among those with a low BMI (18.5-22.5).

In contrast to previous research, the study found no significant increase in mortality for the “underweight” category.

While previous research estimated that 2 to 3 percent of deaths among American adults were due to a high BMI, their study puts the toll at eight times higher.

Masters said he hopes the research will alert scientists to be “extremely cautious” when drawing conclusions based on BMI. But he also hopes the work will draw attention to what he sees not as a problem for individuals alone to solve but a public health crisis resulting from an unhealthy or “obese” environment in America. .

“For cohorts born in the 1970s or 1980s who have lived their entire lives in this obesogenic environment, the prospects for healthy aging in old age just don’t look good,” he said. “I hope this work can influence high-level discussions about what we can do about it as a society.”

The text of this story is published from a wire agency feed without any modification.