Read related article: Beauty from within

ALCOHOL
When your liver has to process excessive alcohol, it produces free radicals, says Esther Blum, MS, RD, author of Eat, Drink and Be Gorgeous (Chronicle, 2007). Limit yourself to one drink per day.

SUGAR
Sucrose (and other sweeteners') molecules bond to collagen, stamping out skin's elasticity and contributing to sags and wrinkles. Plus, eating high-glycemic foods, such as white rice and pasta, triggers hormones that can aggravate factors that potentially lead to acne, according to a recent study published in Molecular Nutrition and Food Research. Find details on sugar's effect on the body at deliciouslivingmag.com; enter the sugar debate into the search box.

NICOTINE
Beyond the free radicals produced by cigarette smoke, the stimulant nicotine can prevent you from getting your beauty rest, which may contribute to weight gain, says Lisa Drayer, RD, author of The Beauty Diet (McGraw-Hill, 2009).

HYDROGENATED OILS
In addition to triggering inflammation, these chemically altered fats — often found in processed foods — can lower your body's ability to metabolize sugars correctly, ultimately leading to weight gain, according to Blum.