People should be even more concerned about being overweight than they already are. Researchers have unintentionally tended to minimize the unhealthy effects of being overweight — but now there's evidence that it is even worse for our health than we think.
Most studies on weight only look at a person's current weight or BMI, not their long-term weight history. That's like conducting a smoking study and only focusing on whether someone is smoking today. This risks overlooking the damage that years and years of prior smoking can do.
Likewise, studies that consider only a person's current weight obscure the damage that being overweight at an earlier time of life —and for a longer period — can do.
The authors of a new study offer mortality figures that illustrate how this snapshot approach minimizes the long-term effects of being overweight.
Using information from the large-scale 1988-2010 National Health and Nutrition Examination Survey (NHANES) and death certificate records through 2011, researchers found that normal weight people who had been overweight at some point in their life (excluding pregnancy) had a 27% higher death rate than normal weight people who had never been overweight. Just being overweight apparently raises the risk of dying, even after those extra pounds are shed.
Normal weight people who had been overweight at some point in their life (excluding pregnancy) had a 27% higher death rate than normal weight people who had never been overweight.
Weight at the time of the survey was a poor predictor of mortality compared to a person's lifetime maximum weight.
Being fat stresses the entire body. And while shedding those extra pounds is healthy, it doesn't eliminate the effects of that prior stress.
“The simple step of incorporating weight history clarifies the risks of obesity and shows that they are much higher than appreciated,” the lead author, Andrew Stokes, said in a statement.
This reasoning comes from looking a little deeper at the individuals in the NHANES survey who had lost weight. There was a much higher death rate and a higher incidence of both diabetes and heart disease among people who had once been overweight (or obese) and had then lost weight than in the people who remained overweight or obese.
The simplest explanation for this is that many of the people who had lost weight and become normal weight (over a third of the normal weight people fell into this category) did so because they were sick.
To sum up, studies that only look at someone's current weight ignore the effect of obesity at an earlier age and also may ignore the fact that weight loss is often caused by illness. The authors urge more researchers to use weight histories instead of current weight in their studies to give a more accurate picture of the health effects of being overweight.
An article on the study appears in the Proceedings of the National Academy of Science (PNAS) and is freely available.