Norwegian University of Science and Technology and SINTEF News, 06/02/2016

It’s a myth that people who weigh a bit more than average live longest. A recent analysis of 30 million people shows that those who had a normal weight had the lowest risk of premature death.
A research report showing that people with a body mass index (BMI), which corresponds to being overweight (BMI 25–30) live longer than people with a normal weight (BMI 18.5–25) was a sensation in both Norwegian and international media a few years ago. The study also showed that people with a BMI that means they are moderately obese (30–35) were at no higher risk of early death than people with a normal body weight, and that this risk only increases for people who are extremely obese (with a BMI greater than 35). A research team consisting mainly of researchers from NTNU in Trondheim has taken a second look at the matter, picking out the weaknesses that the previous analysis had. The analysis involved over 30 million people, and they’ve come to a quite different result. If everyone who has smoked at some point in their life is removed from the analysis, the risk of early death is suddenly lowest at a BMI of 23–24. When the researchers removed everyone who had a chronic illnesses at the time that the BMI data was collected, they found the lowest risk of premature death was at a BMI of 22–23. And when they only included studies with a long follow–up, only healthy non–smokers with a BMI between 20 and 22 don’t have to worry about dying prematurely as a result of their extra kilos.