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THAT'S ONE REASON WHY THE process of getting olestra approved has taken nearly a quarter-century, a pace some in the food industry consider outrageously glacial. It was way back in 1959, in fact, that biochemists at P&G's Miami Valley research campus, near Cincinnati, Ohio, began trying to understand how the body digests fat. In particular, they were trying to identify a kind of fat that premature infants might digest more easily.
The scientists already knew that fats belong to a class of compounds known as esters, which are made from acid molecules linked with alcohol molecules. So they started tinkering with the number of fatty acids that could be attached to a molecule of alcohol. In the process, they made an unexpected discovery. In laboratory animals, an ester composed of an alcohol and one fatty acid was pretty well digested and absorbed. But two fatty acids were better, and three were better still. The chemists reasonably assumed they could keep adding more.
Wrong. As soon as the scientists added a fourth fatty acid, the digestibility and absorbability of the compound decreased. Five fatty acids decreased it further still. And six fatty acids, attached to a molecule of sorbitol, a sweetish alcohol used in food products, made the compound completely indigestible.
That seemed pretty interesting, so the scientists started casting about for cheaper off-the-shelf compounds that had characteristics similar to their rather expensive sorbitol construct. They eventually came up with sucrose polyester, a class of compounds that sports as many as eight fatty acids crowded around alcohol groups that hang, in turn, off a ring of sucrose molecules. By contrast, the naturally occurring fats known as triglycerides include just three fatty acids.
Why does the body digest and absorb triglycerides but not a sucrose polyester such as olestra? Both types of molecule, explains P&G chemist Ron Janacek, are too large to pass unaltered through the mucous membrane of the small intestine and into the bloodstream. With triglycerides, an intestinal enzyme known as lipase acts as a kind of molecular scissors, fitting into slots between the fatty acids and snipping them apart. But when there are too many fatty acids clumped too close together, as happens with olestra and other types of sucrose polyester, these slots are concealed and the enzyme cannot do its job.
Although olestra passes through the intestines undigested, its effect in the mouth is like that of any oil. Oils have a strong chemical affinity for the aromatic compounds that give food its taste and smell; they extract these substances, spread them around the taste buds and waft them up to odor receptors in the nose. Oils derived from plants sometimes have aromatic compounds in them to start with, which is why olive oil, for example, has a distinctive flavor. Others, such as canola oil--and now olestra--have no taste of their own.