I TOTALLY understand causation vs correlation my friend. If you're deep into epistemology you'll understand that ALL of science is essentially correlation.

The reason is simple, let's say the sun rises at let's say 5 AM every morning. This has happened for all of humanity's years but again, we can't say this is 100% true since we don't know the future.

What we call "causation" is frequentive based probability. If you look at things from a bayesian perspective, nothing is certain.

Well, I went off on a tanget there. But again, my point remains.

The study I mentioned is well, correlation. But with other studies finding similar results, it's only sane to deduce a link between sleep and fat loss.