In a new study, researchers found that people who start adulthood with a body mass index (BMI) in the normal range and move later in life to being overweight—but never obese—tend to live the longest.
Adults in this category lived longer than even those whose BMI stayed in the normal range throughout their life.
Those who started adulthood as obese and continued to add weight had the highest mortality rate.
The research was conducted by a team at The Ohio State University.
In the study, the team used data on 4,576 people in the original cohort of the Framingham Heart Study, and 3,753 of their children.
The heart study started in 1948 and followed participants through 2010. Their children were followed from 1971 to 2014.
In both generations, the researchers looked at data from those aged 31 to 80. The main measure was BMI, which is based on a person’s height and weight and is used as a rule of thumb to categorize a person as underweight, normal weight, overweight or obese.
The researchers found that the older generation generally followed one of seven BMI trajectories throughout their lives.
The younger generation had six trajectories—there were not enough people who lost weight through their lives to have a downward weight trajectory as was present in their parents’ generation.
The researchers then calculated how each BMI trajectory was related to mortality rates.
In both generations, those who started at a normal weight and moved to be overweight later in life—but never obese—were the most likely to survive.
Those who stayed at normal weight throughout life were the next most likely to survive, followed by those who were overweight but stayed stable and then those who were at the lower level of normal weight.
In the older generation, those who were overweight and lost weight came next.
The least likely to survive were two trajectories involving those who started as obese and continued to gain weight.
The team says the impact of weight gain on mortality is complex. It depends on both the timing and the magnitude of weight gain and where BMI started.
The main message is that for those who start at a normal weight in early adulthood, gaining a modest amount of weight throughout life and entering the overweight category in later adulthood can actually increase the probability of survival.
But the study showed worrying trends for the younger generation, who are becoming overweight and obese sooner in their lives than their parents did and are more likely to have deaths linked to increasing obesity.
One author of the study is Hui Zheng, an associate professor of sociology.
The study is published in the Annals of Epidemiology.
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