How reliable is the claim that the optimal BMI is 27 because it correlates with maximum life expectancy?
The other day I read a short article in a German magazine citing a doctor called Werner Bartens. He mentions studies that point to the fact that an BMI of 27 is optimal for longevity. Unfortunately the names of the studies were not given and when researching the issue online all I get are the standard claims that a BMI of 20 to 25 indicates optimal weight.
Werner Bartens seems to have a good reputation. He got an MD both in Germany and in the US. The German Wikipedia page lists several awards in science journalism.
Does this point an ongoing controversy?
Which BMI studies are reliable?
This question is in the General Section. Responses must be helpful and on-topic.