The taste of fat may pose a heart risk.

Simply tasting fat-not even swallowing it-can alter the way the body processes fats already in the stomach, according to a new study in humans. That sensory stimulation boosted both the concentration of triglycerides, a class of fatty substances in the blood, and the period during which it remained elevated. Large amounts of triglycerides in the blood are thought to increase a person's risk of coronary heart disease.

These findings confirm effects in rodents reported a decade ago by others. They also suggest the possibility of a previously unrecognized health benefit in fake fats, observes Richard D. Mattes of Purdue University in West Lafayette, Ind., who conducted the new study.

On 4 separate days, he took blood samples before and 2, 4, and 6 hours after each of his volunteers-six men and nine women-swallowed capsules containing 50 grams of safflower oil. On 3 of the days, after they ingested this untasted fat they tasted saltines, saltines with regular cream cheese, or saltines with fatfree cream cheese. Each participant tasted each food, one per day, in a randomly assigned order. After chewing for 1 minute, each volunteer spat out the food.

Mattes tested for changes in concentrations of both cholesterol and triglycerides in the blood as the safflower oil was digested, but only the triglycerides varied from test to test, he reports in the June American Journal of Clinical Nutrition. After volunteers tasted the crackers with full-fat cream cheese, their triglyceride concnentrations rose an average of 60 to 100 percent, compared to readings on the other 3 days. This response cannot be attributed to the tasters' identification of fat, Mattes points out. In separate taste tests with 10 of the volunteers, he found that only one individual could reliably distinguish between the commercially available regular and fatfree cheeses that he used.

Such data pose a conundrum, he admits, because there has been a dogma in nutrition science that fat is perceived by the way it feels in the mouth rather than by any chemical sensor. Yet the fact that his volunteers could not tell the cheeses apart suggests, Mattes says, that something in the mouth is responding to features other than recognized texture.

"This isn't as crazy a possibility as it sounds," says biopsychologist Israel Ramirez of the Monell Chemical Senses Center in Philadelphia, who had conducted the earlier rat studies. "There are sensory capacities that we're not [consciously] aware of" that can alter food digestion. They probably developed, he says, as a way to warn the gut of the impending arrival of food that must be broken down.

That's certainly the implication of a study to be published next month by physiologist Karen L. Teff, also of Monell. She reports that tasting, but not swallowing, peanut butter triggers the production of a small amount of extra insulin. It facilitated the breakdown of sugar that she had deposited untasted (using gastric tubes) into the stomachs of her human volunteers.