Obesity shortens lifespans for every demographic, with one possible exception. According to Jiska Cohen-Mansfield and Rotem Perach of Tel Aviv University, excess weight is protective for people age 85 and older. I have my doubts.
First, let’s explain the study. From 1989 to 1992, the researchers enrolled 1369 people who were then between 75 and 94 years old. At that time, interviewers measured participants’ height and weight and calculated their body mass indices (BMI). People with a BMI of less than 22 were considered to be underweight, those with a BMI of 22 to 30 were considered to be of normal weight and people with a BMI above 30 were considered to be obese. Over the next 20 years, the researchers recorded who lived and who died.
The association between mortality and obesity broke into two groups. For those who had been 75 to 84 at the time their information was collected, obesity increased the risk of death compared to normal weight people. For those who had been 85 to 94, obesity very slightly decreased the mortality risk. Underweight people of all ages had higher mortality rates than normal weight people.
So why am I skeptical? My biggest concern is that the study includes only a single data point for each participant, taken on the day that person was enrolled in the study. In other words, we have no idea whether people had been obese all their lives or had gained weight late in life. We don’t even know whether people who had been obese or underweight at the start of the study stayed in that same category for the rest of their lives. It’s hard to imagine that this information would not play a critical role in evaluating mortality risk. Someone who maintains a normal weight until age 83 and then becomes obese is probably not going to have the same health risks as someone who has been obese from childhood.
That said, I suppose it could be true that obesity prolongs your life once you reach the age of 85. Unfortunately, that same excess weight will most likely prevent you from making it to that age in the first place. My conclusion is that if you are approaching your 85th birthday, by all means have that extra piece of pie.