INEXPLICABLE WEIGHT GAIN You stay away from burgers and drink diet soda. But sugar—both real and artificial—is the secret saboteur. When the pancreas senses sugar, the body releases insulin, which causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen for energy. Eat too much at once, though, and insulin levels spike, then drop. The aftermath? You feel tired, then crave more sustenance to perk up. Faux sugars don't help. "Artificial sweeteners travel to the part of the brain associated with desire but not to the part responsible for reward," says Dr. Gene-Jack Wang, a researcher at Brookhaven National Laboratory in Upton, New York. Nor do they trigger the release of the satiety hormones that real sugar does, so you're more likely to consume more calories.
THE FIX Feed sweet cravings with fruit (the fiber will help keep insulin in check), and sub in sparkling water for diet soda. If you must indulge, go for a small snack made with real sugar, and eat slowly. Add fruit or yogurt to feel fuller and prevent a crash.
BRAIN FOG Blanking out in the middle of a meeting? Research out of the University of California, Los Angeles, suggests that sugar forms free radicals in the brain's membrane and compromises nerve cells' ability to communicate. This could have repercussions in how well we remember instructions, process ideas, and handle our moods, says Fernando Gómez-Pinilla, Ph.D., author of the UCLA study.
THE FIX Stay under the USDA limit of 10 teaspoons (40 grams) of added sugar a day. Read labels and available nutrition information at chains: A 16-ounce Starbucks vanilla latte and Einstein Bros. bagel will max out your day's allotment! A wiser choice: black coffee and plain yogurt with antioxidant-rich blueberries and walnuts, sweetened with honey.
AGING SKIN Sugar causes premature aging, just as cigarettes and UV rays do. With young skin (generally under 35), when skin support structures collagen and elastin break down from sun or other free-radical exposure, cells repair themselves. But when sugar travels into the skin, its components cause nearby amino acids to form cross-links. These cross-links jam the repair mechanism and, over time, leave you with premature wrinkles.
THE FIX Once cross-links form, they won't unhitch, so keep sugar intake to as close to zero as you can. "It's the enemy," says Dr. William Danby, a dermatologist with Dartmouth Medical School in New Hampshire. Avoid soda and processed pastries and trade sugar packets for cinnamon—it slows down cross-linking, as do cloves, oregano, ginger, and garlic.
A SLUGGISH WORKOUT Muscles need sugar for fuel, so carbs (which break up into glucose, a type of sim-ple sugar) can kick-start your morning jog. But fruit or prepackaged snacks touting "natural sweeteners" contain just fructose, which is metabolized in the liver, not the muscles. The result: bloat, or even the runs.
THE FIX A glucose-packed snack with just 4 to 8 grams of fructose—it'll help increase glucose absorption, says Dr. Richard Johnson, professor of medicine at the University of Colorado, Denver. Try a sports drink like Gatorade or trail mix with dried fruit an hour before your workout.