A new study offers more evidence about the importance of managing your weight across your lifetime — particularly about not letting extra pounds creep up on you during middle age.
Yes, yes, this may seem like an obvious (duh!) finding. Yet, although studies have long shown an association between obesity and an increased risk of early death, not much research has been done on the role that the trajectory of our weight across our lifetime plays in the development of that risk.
Five distinct categories
The study, which was published last week in the journal BMJ, analyzed data collected from 80,266 women and 36,622 men who were participating in two large, long-running studies, the Nurses’ Health Study and Health Professionals Follow-Up Study. The data included the participants’ body mass index (BMI) measurements from the time they entered the studies, as well as their recollections of their body shape at earlier ages (5, 10, 20, 30 and 40). The participants also filled out detailed questionnaires about their diet, lifestyle and medical history every two to four years.
The data revealed five distinct trajectories of body shape from age 5 to age 50:
- Lean-stable: These were people who were lean in childhood and stayed lean (with only a slight increase in body shape) throughout their lives. Among the study’s participants, 35 percent of the women and 25 percent of the men fit this category.
- Lean-moderate increase: This group (29 percent of the study’s women and 17 percent of the men) experienced a moderate increase in body shape by middle age.
- Lean-marked increase: This group started life lean, but gained a substantial amount of weight as they moved toward middle age. Eleven percent of women and 17 percent of men in the study fit into this category.
- Medium-stable/increase: These were people who had a medium-sized body shape in childhood and then maintained or gained some weight over time. Among the study’s participants, 29 percent of women and 28 percent of men fell into this group.
- Heavy-stable/increase: This category included people (6 percent of the women in the study and 13 percent of the men) who had a heavy body shape in childhood and then remained heavy — or got heavier — during adulthood.
Body shape and early death
The study’s authors then looked at which participants died in the 15 to 16 years after they passed their 60th birthdays. They found, perhaps not surprisingly, that people who remained heavy from age 5 to 50 had the highest risk of death later in life, whereas those who maintained a lean body shape throughout their lifetime had the lowest mortality.
Furthermore, this increased risk was more striking among people who had never smoked than among those who had. (Smoking can skew findings regarding weight and mortality. That’s because people who smoke tend to be leaner than non-smokers, but they also, of course, tend to die earlier from smoking-related health problems.)
Specifically, the researchers found that the 15-year risk of death for the study’s participants who remained lean throughout their life was 11.8 percent in women and 20.3 percent in men. But the risk was significantly higher for those who reported being heavy in childhood and who remained heavy into middle age: 19.7 percent for women and 24.1 percent for men.
Notably, the data also revealed that even people who were lean in childhood or adolescence but who gained weight in middle life were at higher risk of dying before their 75th year.
For example, the 15-year risk of death for people who started life lean but who then gained a marked amount of weight by middle age (the lean-marked increase category) was 16.7 percent in women and 27.2 percent in men.
For men in this study, going from lean to heavy over a lifetime was even riskier than staying heavy from childhood.
“Our findings provide further scientific rationale for recommendations of weight management, especially avoidance of weight gain in middle life, for long term health benefit,” the researchers conclude.
The BMI with lowest mortality rate
In another study published in the same issue of BMJ — this time a large meta-analysis of 230 previous studies involving 30.3 million participants and 3.74 million deaths — researchers determined that people with a BMI in the range of 20 to 22 have the lowest mortality rate. (Smokers were not included in this study.)
This is a highly discouraging finding — and one that puts into stark focus the gravity of the current obesity epidemic in the United States. More than 70 percent of American adults are either overweight or obese — in other words, they have BMIs of 25 or above — according to the Centers for Disease Control and Prevention.
And, yes, BMI may not be most accurate tool for measuring body fat in individuals, but its use in populations does provide a broad assessment of where we are as a nation in terms of our collective weight problem — and just how challenging it’s going to be to find effective ways to resolve it.
FMI: You can read both studies on the BMJ website.