Did they control for weight? Because overweight and obese people are likely to have both shorter lifespan and more sedentary lifestyle.
Overweight people (bmi 25-30) live longer. I bet they will eventually change bmi classifications to make that range normal. Underweight and obese people live less. But even there obese are probably better off than underweight. Being overweight is in itself exercise for the heart and your calves and every other muscle probably.
Seems statistically dubious..
Is this claim based on a longitudinal study? Or at least does this exclude everyone who lost weight due to health reasons etc.?