A technique to coat droplets of fat or oil with layers of dietary fiber may prevent these substances from being digested. The technology might allow compounds that would ordinarily be destroyed in the stomach, such as certain vitamins or drugs, to be delivered intact to the lower digestive tract. Some scientists think that this encapsulation approach could also lead to tasty but nonfattening food products.

A team of food scientists at the University of Massachusetts, Amherst, has been developing the technology as a way to stabilize fats so that they hold up better during food processing procedures, such as freezing and drying.

To produce the fiber-coated fats, the researchers first create an emulsion--a solution of tiny fat or oil droplets suspended in another liquid--and stabilize it using an electrically charged surfactant that sticks to the surface of each droplet. Then fiber particles with an opposite charge are added to the mix. Electrostatic forces cause the fiber to adhere to the surfactant-coated droplets, creating a protective layer.

"We had the idea that if you did that, and the dietary fat was indigestible, then you could have these low-fat products," says food scientist Julian McClements, who led the research. If the dietary fiber can pass through the gastrointestinal tract undigested, the fat droplet contained within it will go undigested as well, and thus not contribute to weight gain. In this way, the food's effective fat content would be lower than its actual fat content.

Paul Takhistov, a Rutgers University food scientist who was not involved in the research, says that stabilizing emulsions by coating droplets with various substances is a common procedure in the food industry. "But the idea to use such an approach to mask fat and prevent its digestion is really, really new," he says.

Nutritionists often recommend limiting fat consumption to 30 percent of an individual's caloric intake, a suggestion that has spurred the creation of a wide variety of reduced-fat foods. But consumers tend to find these foods disappointing, as they lack the flavor and texture of their full-fat counterparts. "Fat has a physical effect on food products; these tiny droplets of fat affect the texture and the sensory quality of the product," says UC Davis food scientist Moshe Rosenberg, who was not involved in the research.

The resulting quest to create nonfattening substances that nonetheless smell, taste, and behave like fats has been fraught with costly failures. Sales of foods containing the indigestible fat substitute olestra, marketed by Procter & Gamble as Olean, suffered dramatically when the FDA mandated a warning label disclosing its possible side effects: diarrhea and loose stools. The FDA lifted the requirement in 2003.

McClements hopes to hone the fiber coating so that the fat's texture, taste, and aroma are unaffected, and at the same time guard against unwanted side effects. Maintaining the texture is likely to be the most straightforward of these challenges. According to Takhistov, our tongues can't sense particles smaller than 30 microns in diameter. The coated droplets, which range from about 100 nanometers to 3 microns, are much smaller. And because the thin fiber coating adds very little bulk to each droplet, the physical properties of the emulsion should be unaltered.

Preserving taste and smell could prove more difficult. Rosenberg says that if the fat is sealed tightly enough to prevent digestive salts and enzymes from getting in, the compounds that lend it flavor and aroma will be locked inside as well. "If you take the fat and you lock it in a way that prevents release of its flavor and aroma, the product is completely different," says Rosenberg.