By Emily Sohn
October 04, 2010

Who doesnt want a magical weight-loss pill that would make calorie counting, treadmill workouts, and sacrifices unnecessary? We all do. Thats why weight-loss dietary supplements are a $3.8 billion industry. But with little federal regulation and few long-term human studies to back them up, the actual effectiveness of supplements is still open to debate.

Still, “some of them can be very useful aids to a good diet-and-exercise program,” says Harry Preuss, MD, a professor of medicine at Georgetown University and author of The Natural Fat Loss Pharmacy. Here, what the experts say about the supplements with the most promise.

How it worksWhat to expectHow much to takeKeep in mind
Green teaThe key is ECGC, an antioxidant in green tea that helps your body burn more calories by ramping up your metabolism.Several small studies suggest that ECGC helps burn an extra 180 calories a day-enough to help you lose 18 pounds in a year.Take 325 milligrams per day (along with 100 mg of caffeine, which seems to improve the effects) in three installments before meals.Too much caffeine can lead to anxiety, high blood pressure, and insomnia.
Linoleic Acid (CLA)CLA-a natural component of meat and milk from cows, goats, and lamb-seems to prevent fat from being deposited in fat cells. According to studies of rats, CLA attacks abdominal fat.A yearlong study in 180 healthy overweight people (mostly women) showed an average loss of 4 pounds and 9 percent body fat.The usual recommendation is about 3 grams per day (about three pills) with meals.CLA may raise levels of the inflammatory marker C-reactive protein, which could up your risk of heart disease.
Hydroxycitric Acid (HCA)Found in a number of tropical plants, HCA blocks an enzyme that turns carbs into fat. HCA may also increase levels of the feel-good chemical serotonin in the brain, dampening the urge to overeat.An eight-week study found that taking HCA while eating 2,000 calories a day and walking five days a week helped participants lose 8 pounds and 5 percent of their body mass index.Calcium and potassium help with HCA absorption, experts say, so try a supplement that combines these ingredients; take 2.8 grams per day, split into three doses, right before meals when your stomach is empty.Very high doses may upset your stomach, but there are no serious side effects.
ChromiumThis mineral is an essential nutrient that helps regulate insulin-a hormone responsible for transporting sugar out of the bloodstream and into the cells. Chromium seems to help boost metabolism.You may not lose weight, but your clothes may fit better! Some studies show that chromium helps people lose fat, not muscle; you'd lose both with a typical diet.A 600-microgram daily dose, divided into three parts, is best if you're trying to lose weight; for maintenance, switch to 200 mcg a day. Always take it between meals and separately from other multivitamin and mineral supplements.Many weight-loss studies fail to show a benefit, but experts like Dr. Preuss believe chromium builds muscle.
FiberBecause it consists of the indigestible parts of plants, fiber helps you feel full. It also may produce fat-burning by-products in the colon.Tufts University researchers found that getting 14 additional grams of fiber each day helps people eat about 10 percent fewer calories and lose 5 extra pounds in four months.Aim for about 35 grams of fiber a day, mostly from whole grains, fruits, veggies, and beans. If your diet is weak on fiber, taking a supplement such as psyllium three times a day with meals might help.Drink plenty of water with your fiber or you'll end up with digestive troubles.
Resistant StarchIt's actually a type of fiber (see above) that your body doesn't absorb. Resistant starch is found in foods like cold cooked potatoes, navy beans, and lentils, and it provides the same benefits as fiber.How much weight you can lose is unclear, but the effects may be similar to those of regular fiber.Experts say Americans get 3 to 8 grams per day but could benefit from double that amount.Resistant starch isn't available in pill form, but you can buy it in bulk and add it to food or smoothies. Too much could lead to bathroom troubles.
AlliThis nonprescription med prevents the intestines from absorbing about 25 percent of the fat in your diet. Instead, it just runs through your system.Estimates by the Mayo Clinic suggest you'll lose an extra 3 pounds in a year if you use Alli while dieting and exercising.Take one (60-milligram) pill with meals up to three times a day.Fat should make up no more than 30 percent of your diet. Otherwise, you can end up with greasy stools.