Ten Pounds in 10 Days?

By Rachel Johnson, Ph.D., M.P.H., R.D.

Can you safely fast-track weight loss?

"Lose 10 pounds in 10 days!" As a nutrition professor, I know better than to believe the ultra-fast weight-loss claims that proliferate as bathing-suit season peaks. I admit, some of the ads sure sound compelling. I've long wondered if any of the products that promise to "zap fat like magic" might have a kernel of truth. My friend Jane nips weight gain in the bud with a once-a-year three-day juice fast; it seems to work for her—but what does the science say? Full of hopeful skepticism, I recently sorted through the more enticing claims.

Fasting: "The perfect jump-start!"

People have fasted for centuries, mostly for religious reasons. But these days, short-term fasting to lose weight is much more common.

At first blush it sounds like a good strategy: in a 2002 study by ­scientists at the Rowett Research Institute in Aberdeen, Scotland, healthy adults lost 1 to 2 percent of their body weight during a 36-hour fast (during which they consumed nothing but water) and up to 5 percent in six days. The subjects’ feelings of hunger and fatigue increased with the length of the fast—contradicting the argument often heard that hunger fades with prolonged fasting. Most discouraging, though, was that the fasters lost mostly muscle, not fat.

Juice fasts like Jane’s may be better at curbing hunger since they ­provide some calories: most juice fasts recommend four 12-ounce glasses of fruit and/or vegetable juice in addition to water—better but hardly a nutritious menu by any standard. You should only fast if you are otherwise healthy and any prolonged fast should be medically supervised.

Fat Burners: "Rev up your metabolic rate to 'burn' stored fat!"

We've all seen the claims that fat burners—which usually include some sort of stimulant—raise your metabolic rate so you burn fat faster. But when you stoke metabolism you also risk straining the heart—a lesson we learned in 2003 when studies found that ephedra, one of the most popular fat burners, has dangerous side effects including heart attacks, strokes and even death. The Food and Drug Administration subsequently prohibited its sale.

Today’s fat burners usually contain milder stimulants. One, Citrus aurantium (bitter orange), is touted as a safer alternative to ephedra, but a recent review by researchers at Johns Hopkins School of Medicine concluded that more and larger studies are needed to determine the herb’s effectiveness and safety. Caffeine, another common addition to fat-burner formulas, boosts metabolism only minimally. In a 2007 study, 50 mg of caffeine (the amount in 1⁄2 cup of coffee) increased subjects' calorie-burning rate by about 6 percent. That comes to about 17 extra calories burned off during the four hours the subjects were tracked. But those ­results may be misleading, since the subjects’ usual intake of coffee was low. As any Starbucks regular can tell you, people with a regular caffeine habit are less stimulated by caffeine.

Fucoxanthin, a compound found in brown seaweed, is reported to act differently from the stimulant-type fat burners, although its precise mechanism is still unclear. Animal research from Hokkaido University, Japan, found that abdominal fat was slightly reduced in rodents after they were fed fucoxanthin. Although this sounds promising, it’s too early to tell if humans will benefit too.