Is gradually gaining weight a longevity hack?
The findings, published in the Annals of Epidemiology, are based on an individual’s body mass index (BMI), which is a measure of body fat based on height and weight that classifies adult men and women as underweight (BMI below 18.5), normal weight (BMI 18.5 to 24.9), overweight (BMI 25 to 29.9) or obese (BMI 30 and above).
To get at the results, researchers used data from the Framingham Heart Study, a long-term study based in the town of Framingham, Mass. that set out to discover the underlying causes of heart disease by following the medical histories of the participants and their children. Both the original 4,576 study participants and 3,753 of their children were included in the latest analysis as the researchers looked at the BMI trajectories of both groups from 31 to 80 years old.
The study authors found that, in the original group from the Framingham Heart Study, “people who are normal weight at age 31 years and gradually move to overweight status in middle or later adulthood have the lowest mortality risk, even compared to those who maintain normal weight throughout adulthood,” according to the study. The same was true for the offspring of the original group.
This was followed by people who are considered overweight but were able to maintain a stable weight. Next came people with a “lower level” of normal weight and those who were overweight as adults but then lost weight over the years. People who were obese in early adulthood and then gained more weight with age showed the highest mortality rate.
So why would a BMI that slowly goes up over time be potentially more protective? “Moderate weight gain among those who are normal weight in early adulthood may confer some survival benefits,” lead author of the study, Hui Zheng, assistant professor of sociology at The Ohio State University, tells Yahoo Life. “[This] is consistent with the view that modest extra body weight in old ages, including lean tissue mass and fat mass, might provide protection against nutritional and energy deficiencies, metabolic stresses, the development of wasting and frailty and loss of muscle and bone density caused by chronic diseases such as heart failure.”
In addition, Dr. Samer Mattar, professor and chief in the division of metabolic and bariatric surgery at Baylor College of Medicine, points out that “not all weight gain is represented by fat mass.” Mattar tells Yahoo Life: “These subjects may have had their weight gain attributed to muscle mass. Moreover, these subjects probably enjoyed better nutritional profiles rendering them more immune to many disease processes, and offer[ing] protection from various nutritional deficiencies, as opposed to people who might have unintentionally lost weight due to illness, or those who gained a large amount of weight, and as a result of their obesity and metabolic syndrome, developed life-threatening diseases such as diabetes, hypertension and sleep apnea.”
In other words, using BMI as a standard metric has its limitations. “The BMI cannot distinguish between fat and muscle mass,” Mattar explains. “A healthy muscular football player may have the same BMI as a person whose body composition is mainly fat. Also, the BMI at any given time is a snapshot in time. It’s more helpful to study the BMI profile of a person over time, say, since childhood or adolescence rather than at only one time point. People who have been obese for longer periods tend to have a higher burden of disease.”
The study also highlights both good and bad news about obesity and mortality rates. Zheng tells Yahoo Life that the “obesity-related mortality rate has declined across generations.” Mattar explains this is “probably as a result of the decline in infectious diseases — COVID notwithstanding — against which people with obesity have reduced immune responses.” Mattar adds: “There is also overall greater awareness of obesity comorbidities, and patients tend to now be better treated for potentially lethal conditions such as hypertension, diabetes and sleep apnea.”
However, the study also found one important difference between the two generational groups: Unlike with their parents' generation, more people in the study’s offspring group are “in the obesity trajectory,” according to EurekAlert. “Even though obesity-related mortality has declined across generations, the percentage of deaths caused by obesity has increased because the prevalence of unhealthy weight trajectories has increased,” Zheng tells Yahoo Life.
Zheng notes that the effect of weight gain on mortality is “complex.” He says, “It depends on timing and magnitude of weight gain and baseline weight status in early adulthood. For people with normal weight in early adulthood, moderate weight gain into overweight in later adulthood is associated with lower mortality risks compared to those who remain in the range of normal weight over the course of adulthood. But, for people with overweight or obesity status in early adulthood, weight gain is associated with excessive mortality risk.”
Mattar says that it’s “critical” for people to pay attention to “what and how they eat.” He recommends practicing “moderation” in both food choices and portion sizes, along with maintaining adequate physical activity levels as much as possible. “Being a little overweight is permissible, but this should be monitored and patients should seek medical counseling should their weight enter into more concerning territory, meaning BMI of over 35,” says Mattar.
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