How they work: You order vegetable and fruit beverages from one of the ubiquitous juice-cleanse companies like BluePrintCleanse or Organic Avenue. Then, as you've likely heard from the friend who won't shut up about it on Facebook, for three to five days you drink only these beverages. (If you must eat, some companies say certain foods, mostly raw veggies, are OK.)
So do they work (and are they safe)? You might shed, but it'll be mostly water weight. "Nobody should do a juice fast for more than three days," cautions Pamela Peeke, MD, assistant professor at the University of Maryland and author of The Hunger Fix. No matter how many vitamins the juices have, the lack of fat means some of them won't be properly absorbed. If you do repeated cleanses, continues Dr. Peeke, the periods of calorie deprivation could cause a temporary metabolism slowdown. Steer clear if you're pregnant or have diabetes. And know that you could even gain weight if you overdo it with fruit juices, adds Frank Lipman, MD, an integrative medicine specialist in New York City. Even the healthiest fruit juice packs sugar. Case in point: Organic Avenue's Gracious grapefruit juice has 37 grams.
If you want to try one: A three-day juice fast before a big event should be fine, allows Dr. Peeke, but check in with your doctor first. And be aware that these diets can clean you out in more ways than one: They cost up to $75 a day.
How it works: The original is Bikram yoga, a 90-minute series of 26 poses done twice in a 105-degree studio. You'll find other hot yoga classeseither Vinyasa or Ashtanga yoga, given in 90-degree-plus rooms. Proponents claim the high temps help boost metabolism.
So does it work (and is it safe)? "You're going to sweat a ton, then you're going to drink like mad and put back on all the water weight you lost," says Dr. Peeke. As for claims you'll burn fat faster? "Your metabolism improves, at least temporarily, with pretty much any exercise." And the heat may make you move less vigorously, notes B. Don Franks, PhD, a fellow of the American College of Sports Medicine: "The more work you do, the more calories you burn." Avoid hot yoga if you have hypertension or heart disease since it can spike blood pressure.
If you want to try it: Stick with power yoga or aerobics for more effective fat-burning. But if you test out hot yoga, drink up: Bikram masters recommend an extra 64 to 80 ounces of water per day.
How it works: This ancient practice has found new life as part of some slimming strategies. A practitioner inserts fine needles along the ear to target "hunger points" that, when stimulated, may impact hormones related to appetite.
So does it work (and is it safe)? "Only in combination with diet and exercise, and the magnitude of added benefit is not clear," says Tieraona Low Dog, MD, fellowship director at the University of Arizona Center for Integrative Medicine. She suggests potential payoffs may be more likely a result of weekly interaction with the acupuncturist: "When someone is accountable, they generally have better success." Of course, checking in with a friend could serve that purpose.
If you want to try it: Go to a reputable provider. Find a list of practitioners at the National Certification Commission for Acupuncture and Oriental Medicine's site, nccaom.org. Sessions cost between $50 and $120; most people go once a week.