Pop pills: Combining regular exercise with fish-oil supplements increases the activity of your fat-burning enzymes, reports a study published in the American Journal of Clinical Nutrition. Volunteers took six grams of fish oil daily and worked out three times a week. After 12 weeks, they'd lost an average of 3.4 pounds, while those who exercised exclusively saw minimal shrinkage. Look for brands containing at least 300 milligrams of the fatty acid EPA and 200 milligrams of the fatty acid DHA per capsule. Pop two of these two hours before your workout.
More: Go Fish
5. When You Get Home
Eat Nemo's pals: Fatty fish like salmon, tuna and sardines are loaded with hunger-quashing omega-3 fatty acids. These healthy fats help trigger the rapid transfer of "I'm full" signals to your brain, according to the National Institutes of Health. Bonus: A 3.5-ounce serving of salmon nets you 90 percent of your recommended daily value of vitamin D, which will help preserve your precious calorie-craving, metabolism-stoking muscle tissue.
More: How to Cook With Sustainable Seafood
Skip the second mojito: Another reason not to over indulge—knocking back the equivalent of just two mixed drinks (or two glasses of wine or two bottles of beer) puts the brakes on fat burning by a whopping 73 percent. That's because your liver converts the alcohol into acetate and starts using that as fuel instead of your fat stores, report researchers from the University of California, Berkeley.
More: The Benefits and Risks of Alcohol
Hit the sack—early: When you sleep less than you should, you throw off the amounts of leptin and ghrelin — hormones that help regulate energy use and appetite — that your body produces. Researchers at Stanford University found that people who snoozed fewer than 7.5 hours per night experienced an increase in their body mass index. So make sure you get at least eight hours of rest.
More: 3 Reasons You Should Sleep More
Race Against Time
Beat the downshift in metabolism that comes with aging: With each passing decade, a woman's metabolism slows by about 5 percent. Hormones play a role, but mostly it's because as you get older, you typically become less active. As a result, you lose muscle mass, a major consumer of all those calories you scarf down. So by the time you hit 35, you'll burn 75 fewer calories a day than you did at 25; by age 65 you'll burn 500 fewer, says Madelyn Fernstrom, Ph.D., director of the Weight Management Center at the University of Pittsburgh. You can outsmart Mother Nature with the tips on these pages. Here's what happens if you don't:
20s:Your muscle and bone mass are at their peak.
30s: Your mitochondria—cellular powerhouses that fuel muscles to use more oxygen and burn more energy—become less effective.
40s: A drop in estrogen production further slows metabolism.
50s: Sharp decreases in activity reduce the levels of hormones responsible for maintaining lean muscle mass and bone density.
More: 3 Workouts to Crank Up Your Metabolism
Stay in shape in a fitness class.