I have thought for years that if I ate too much sugar, I'd probably give myself diabetes. I used to joke about it. Turns out, I was right. :( I highly recommend this presentation outlining the evidence in an easy to "digest" way (pun intended). Science has effectively proven causation (i.e., consuming sugar causes diabetes), to the same standard that causation was proven between tobacco use and related health outcomes.

In my lifetime I expect to see some class action lawsuits related to this.

Is a Calorie a Calorie? Processed Food, Experiment Gone Wrong