Is it safe to say that obesity is a risk factor for diabetes but not a cause?
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Establishing cause for anything is incredibly difficult. You have to be able to rule out conclusively that *nothing else* could be influencing the effects you observe in an experiment. Not random chance, not other factors, not the mere process of recovery or aging. This is very difficult to do. Often all we can see is correlations. Correlations aren’t meaningless, they’re useful information, but they don’t always tell the whole story. You can’t assume all of them are meaningful. Only some of them are meaningful, and it’s sometimes hard to know which is which.
All a “risk factor” is is a factor keeps showing up as a correlation. We keep doing studies that find that obese people are more likely to develop diabetes than non-obese people. We can’t necessarily say for certain. All we know is (making numbers up here) 1 in 5 obese has diabetes but only 1 in 20 non-obese people does. They could be unrelated, we don’t know for sure.
Establishing philosophically-certain cause-and-effect is nearly impossible. However if you keep doing studies over years and years and decades and decades, and you keep finding a correlation over and over again, and you do studies that try to control for this or that factor, and the correlation is always there, then scientists get closer and closer to being willing to say it’s a true cause, and not merely a risk factor. They did a gazillion studies on cigarettes and lung cancer. They keep finding this astonishingly large correlation, the science gets sophisticated, they control for all kinds of factors. And after several decades of this, eventually doctors got comfortable just coming out and saying: smoking causes lung cancer. None of those studies *proved* it beyond a doubt, none are like mathematically-logically irrefutable. But all combined together, no *reasonable* person could possibly doubt it.
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