Sugar overload may kick-start a process called glycation. The theory: When you eat more sugar than your cells can process, the excess sugar molecules combine with proteins, creating "advanced glycation end products" (appropriately referred to as "AGES"), explains Dr. Ostad. Ultimately, AGES may damage your skin's collagen (the protein that keeps skin firm and youthful).
Unsurprisingly, too much sweet stuff is also bad for your smile. "Sugar sticks to your teeth, encouraging bacteria, decay, and discoloration," says Brian Kantor, a cosmetic dentist who practices in New York City. If you treat yourself to something sweet, swish water around your mouth afterward to remove any buildup.