Understanding why hot peppers are slimming

Chilis' fiery compound triggers molecular changes that fight body fat.

There seems little doubt that chemicals responsible for the peppery bite of chili peppers can inhibit the accumulation of body fat. It’s not only been illustrated rather convincingly in rodents, but also reported a few months back to operate in people. The question has been how peppers do this. Korean researchers now describe peppery changes in genes that appear to underlie fat-shunning properties — ones that point to how chili’s fiery chemistry might be harnessed to fight obesity.

FIERY DIET AID The chemical that gives chilis their heat also turns up the body’s furnace so that it burns fat. iStockPhoto

The researchers, all from Daegu University in Kyungsan, fed high fat diets to five-week-old rats for two months. Some got a daily oral injection of dilute capsaicin, the fiery chemical in chili peppers, or just a control — the liquid that had been used to dilute the capsaicin. Throughout the course of the trial, animals getting capsaicin gained 8 percent less weight than untreated animals, and just a fraction more weight than animals eating a normal diet.

Capsaicin-treated animals also developed less body fat and accumulated smaller fat droplets within fat cells. These findings would seem to indicate, the researchers say, “that capsaicin can have a significant inhibitory effect against fat accumulation.”

But again, that’s not enough to warrant a major new paper, since others have reported elements of this. What’s really new in the paper by Jeong In Joo, Jong Won Yun and their colleagues is an identification of which genes are selectively up- or down-regulated — dialed up or down in activity — by consumption of dietary fat or by capsaicin.

They found, for instance, that a high fat diet up-regulated genes producing 17 proteins, including NQO1, heat shock protein 27, vimentin and preoxiredoxin. Some 10 of which were normalized or almost returned to normal in the animals treated with capsaicin. Another 10 of the bunch were down regulated in animals eating high-fat chow. Unless, that is, they also got capsaicin. Then the production of these proteins also came back to normal, or nearly so.

In addition, the activity of several genes that control the production of fat cells were ratcheted down by capsaicin. Meanwhile, this dietary additive boosted the activity of genes associated with turning on the body’s furnace, by accelerating the burning of fat — both the normal white fat and the beneficial brown fat. “To the best of our knowledge,” the authors note, “this is the first report concerning thermogenic [heat production] action of white adipose [fat] tissue in response to capsaicin.”

Some of the proteins altered by capsaicin treatment have been linked to obesity — or its prevention — before. Others appear to be newly identified players. A report of the new findings appears in the June 4 Journal of Proteome Research.

Altogether, the new findings suggest there may be dietary routes to slowing or even reversing obesity and related diseases. And for those of us who can’t handle much of the mouth-burning capsaicin, it’s good to know that it has a peppery cousin that may work as well — with no fiery effects on the mouth or gut (see Chili pepper holds hot prospects for painfree dieting).

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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