Not new, but I’m quoting it anyway because I like it :) From an article on the obesity “health crisis” in the International Journal of Epidemiology:
Imagine that the average IQ was 100 and that five percent of the population had an IQ of 140 and were considered to be geniuses. Now let’s say that education improves and the average IQ increases to 107 and 10% of the population has an IQ of > 140. You could present the data in two ways. You could say that average IQ is up seven points or you could say that because of improved education the number of geniuses has doubled. The whole obesity debate is equivalent to drawing conclusions about national education programmes by saying that the number of geniuses has doubled.
The article also discusses whether fat itself causes disease and how much of weight is under conscious control.