The problem is, you can't do a blind study with diet and exercise, because the subjects will know what they are doing. You could potentially do a caffeine pill

The problem is, you can't do a blind study with diet and exercise, because the subjects will know what they are doing. You could potentially do a caffeine pill study rather than a coffee study, but even that is hard to keep people from detecting. On top of this, we're looking at long term studies that would be really hard to control. Finally, the correlations noticed by these authors need to be taken with a huge grain of salt because there are so many potential confounding factors, such as income.