It downgrades your immune system
Dr. Lipman points to a study showing that eating too much sugar may mean you won't make it through another winter. OK, that's a tad dramatic, but sugar does make it harder for your body to fight off infection "through decreasing activity in immune system cells that attack bacteria," he says. So if you seem to be catching every bug that crosses your path, reexamine your diet plan.
It makes you incapable of self-control
Look, the whole "sugar is a like a drug" isn't just a hyperbolic simile. After a while, your brain becomes obsessed with the natural opioids, or "natural high," that comes with eating a lot of sugar. "A diet loaded with sugar can generate excessive reward signals in the brain which can override one's self-control and lead to addiction," says Dr. Lipman.
It gets worse: 94% of lab rats given the choice between sweetened water (with saccharin and sugar) and intravenous cocaine chose sugar. And even when researchers upped the dosage of cocaine, the rats still chose the water... which is scary, especially because the rats preferred the sweetened water even when they were high on cocaine.