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Science & the Public

Chili pepper holds hot prospects for painfree dieting

It works even though the body never absorbs it

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ANAHEIM — A cousin of capsaicin, the chemical that packs the heat in chilis, not only can rev up the body’s metabolism, but actually encourage it to preferentially burn body fat, according to a new trial in obese men and women. And the kicker: The molecule is itself so fat that it can’t fit into the receptors that would ordinarily register pain.

That means this dihydrocapsiate can’t irritate the mouth or gut, says David Heber of the University of California, Los Angeles. Indeed, the body doesn’t even absorb it, he reported April 27 at the American Society of Nutrition annual meeting.

His team, which administers a Risk Factor Obesity Program, recruited 33 men and women for a university-funded trial with the pepper compound. Under a doctor’s supervision, these volunteers consumed all of their nourishment — a mere 800 calories a day — in the form of a liquid meal-replacement.

At breakfast, lunch and dinner each participant also downed three capsules. One group got placebo pills. Another received capsules containing 3 milligrams of dihydrocapsiate a day. The last group got 9 milligrams a day of the chili-derived compound. Neither the recruits nor the doctors administering the study knew who was getting the chili compound, much less the amount.

At the end of four weeks, each individual fasted and then came into the lab for a meal. Afterward they rested, sitting under a hood at periodic 20-minute intervals over the next four hours while their intake of oxygen and exhalation of carbon dioxide were measured. The ratio of these two gases, known as the respiratory quotient, offers an indirect measure of what the body is burning — protein, fat, carbs or some combination.

Although the meals each dieter had been eating for the past month contained zero fat, the respiratory quotient indicated that at rest the recruits were burning a lot of fat, explains Zhaoping Li, associate chief of clinical nutrition at UCLA’s David Geffen School of Medicine.

Adds Heber, the extra calories burned by dieters getting the high dose of dihydrocapsiate was almost double the value measured in people who had been getting the placebo.

The findings suggest that people in the high-chili group were probably shedding about a pound more per month than those in the placebo group. However, measuring that wasn’t part of this trial — and in fact would be challenging to confirm in such a short study, notes T.Y. Amy Lee, another physician on the UCLA research team. The reason: Most weight loss in these individuals traced to their super–high-protein, low-calorie diet.

So if the body doesn’t absorb the chili supplement, how does it boost metabolism? By temporarily binding with a receptor in the gut (known as transient receptor potential vanilloid-1). When triggered, Heber explains, this receptor sends a signal to the brain, which in turn sets in motion a whole cascade of events that effectively stokes the body’s furnace.

The same process occurs when people eat hot chili peppers — and explains why many actually begin to sweat. In fact, Li says, the capsaicin in smokin’ hot chilis could also be employed to stoke the body’s furnace. But to trigger the magnitude of effect achieved by the dihydrocapsiate in these study participants would have caused intense fiery distress to their mouth and gut, she notes.

In theory, the chili-derived dietary supplement (which is not commercially marketed) could be safely consumed daily, much like a vitamin, Heber says. And while a high dose of it could help a 100-pound woman burn an extra 160 calories per day, he points out that this benefit would be erased by downing a non-budgeted drink or piece of cake. “As I always say,” Heber told me, “a supplement doesn’t make up for diet.” It’s role is to boost the value of diet and exercise.

The ASN meeting, where the data were reported, took place under the aegis of Experimental Biology 2010. (This umbrella conference, sponsored by ASN and five other biomedical research societies, also hosted the annual meetings of another 17 guest research societies this year.)

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