Can you safely fast-track weight loss?

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.

Appetite Suppressants: "Trick the brain into thinking you've eaten!"

Whether they claim to make you feel fuller or help you forget your hunger, many products promise to curb your urge to eat. One that's getting a lot of attention is Hoodia gordonii, a milkweed relative native to South Africa and Namibia. African Bushmen reportedly chew on hoodia stalks to ward off hunger during long hunting trips. Preliminary clinical research is intriguing; mice given injections of P57, a steroid compound identified as hoodia's active ingredient, suppressed their food intake significantly. But for us humans, hoodia's weight-loss effects "are not strongly substantiated by significant large clinical trials," says Roberta A. Lee, M.D., medical director at the Continuum Center for Health and Healing at Beth Israel Medical Center in New York. "That makes the ­evidence weak for weight loss at this time."

The Bottom Line

As I expected, none of the quick fixes had strong scientific backing. So I turned to my friend Jean Harvey-Berino, Ph.D., chair of the University of Vermont's Nutrition & Food Sciences Department and author of The EatingWell Diet (The Countryman Press, 2007). "The best way to give yourself a jump-start," she said, "is to create rules that add structure to your diet." Jean suggested dialing down calories but still eating a balanced diet of real foods. Normally she would say not to drop below 1,200 calories per day, but for a quick fix, you could shave off a few more-going absolutely no lower than 800-for up to 3 days (no longer). She also recommends getting enough protein to prevent muscle loss and curb hunger. (That's easy: most adults need about a third of a gram of protein per pound of body weight each day. For a 150-pound person that's 50 grams-the amount, roughly, in 10 ounces of chicken breast.)

Now when I need to lose a few pounds, I cut my calorie intake to about 1,000, well below my usual. I also add a two-mile morning jog (in addition to my usual noontime exercise class). These changes help me feel more in control and, before I know it, the unwanted pounds come off. It 's not "10 pounds in 10 days" but it does the trick for me.

July/August 2008