1. Artificial sweeteners. Even worse than sugar (which causes a spike in blood sugar, prompting the release of stress hormones), artificial sweeteners such as aspartame contain phenylalanine and aspartic acid, "excitatory nerve transmitters that can keep you up all night," says Lieberman.

2. Caffeine. Avoid tea and coffee, but watch out for caffeine lurking in chocolate, too. Chocolate also contains theobromine, a plant alkaloid with stimulating effects (Psychopharmacology (Berl), 2004, vol. 176, nos. 3-4).

3. Fat. High-fat meals make your digestive system work longer than it should, which can keep you awake. Fat also aggravates heartburn.

4. Liquor. "Initially, alcohol seems calming," says Hyla Cass, MD, "but it disrupts blood sugar levels and interferes with neurotransmitter production, including serotonin."

5. Spicy foods. According to Traditional Chinese Medicine, garlic, hot peppers, and highly seasoned foods are too stimulating to eat before bed. These pungent tastes can also exacerbate heartburn.

Sources: Shari Lieberman; Hyla Cass, MD.