How your BMI backstory predicts your mortality

An interesting new study landed in my in-box the other day, and it was something I hadn’t really thought about in all of my years dealing with overweight and obese patients.

According to this new research, it appears that looking at someone’s current weight doesn’t necessarily give an accurate picture of their health — and especially their risk of death.

You see, most studies calculate the mortality risk associated with obesity based on a single snapshot in time. For instance, when individuals are evaluated for a mortality study, their Body Mass Index (BMI) is recorded at the beginning of the study and at the end. But their overall weight history isn’t involved in the equation. Which means people who have always been at a normal weight are assessed in the same way as people who may currently be at a normal weight but have a past history of obesity.

And, it turns out, not distinguishing the difference between “not currently obese” and “never-obese” can skew the results. And give you a false sense of security in regards to your mortality risk.

Which makes perfect sense.

The mortality studies done on the adverse effects of smoking almost always include three distinct categories of people: Those who have never touched a cigarette, those who currently smoke, and those who were smokers in the past, but quit. And the differences between these three categories are huge.

Yet no one has done this with an obesity study…until now.

In order to get a clearer picture of how obesity (past and present) affects mortality, investigators from the School of Public Health at Boston University and U Penn Philadelphia examined data from two separate National Health and Nutrition Examination Surveys (NHANES) from 1988-1994 and 1999-2004. These studies included 6,300 non-smokers between the ages of 50 and 74. The investigators used 4 different models to examine the relationship between BMI and mortality, and then linked these findings to death records from the National Death Index through 2011.

The overall results showed people who had the highest BMI over any period of time also had the highest risk of death. (I would bet the length of time someone is overweight or obese plays a role too…But I will have to wait for that study to show up in my email one day.)

Specifically, the researchers found that 39% of people who previously had a high BMI had a higher chance of dying early. Which seems to contradict everything we thought we knew about weight. Until you look at the real reason behind the weight loss, that is.

You see, that 39% easily overlaps with the number of overweight and obese people who are at risk for diabetes, heart disease, cancer, etc. So chances are good that when these people did get sick, they lost weight. So they reduced their BMI because of an illness…not because of healthy lifestyle changes.

Still, this study really opened my mind, and showed that obesity can affect you long after you lose weight.

As the investigators said, these “results suggest the burden of overweight and obesity on mortality is likely substantially larger than commonly appreciated. If correct, this may have serious implications for the future of life expectancy in the United States. Although the prevalence of obesity may level off or even decline, the history of rapidly rising obesity in the last three decades cannot be readily erased.”

That said, there is still no better way to positively impact your health than to lose any excess weight you may be carrying.

As I have pointed out numerous times before, there are many, many studies that show getting yourself to a healthy weight will keep you living the longest.