Frequent consumption of potato chips, tortilla chips or other savory snack foods made with the fat substitute olestra is associated with a significant reduction in serum cholesterol levels and dietary fat intake, according to researchers at the Fred Hutchinson Cancer Research Center in Seattle.

The heaviest consumers of olestra -- those who reported eating one to two servings of chips per week for a year -- experienced a decrease in total serum cholesterol of more than 10 percent. These findings appear in the "Archives of Internal Medicine," a publication of the American Medical Association.

"This drop in serum cholesterol associated with olestra use is comparable to that achieved with a high-fiber diet or conventional cholesterol-lowering drugs," says Ruth E. Patterson, Ph.D., R.D., an associate member of the Hutchinson Center's Public Health Sciences Division and the report's lead author.

While intriguing, the researchers caution that their results are preliminary, based on first-year data from several hundred participants in an ongoing nationwide study to monitor use patterns and nutritional effects of olestra consumption in the general population. Once the four-year study is complete next year, some 12,000 Americans will have participated at four clinical sites around the country.

The researchers also caution that while eating olestra may have a biological, cholesterol-lowering effect, it also may be an indication of a healthier lifestyle; people who eat olestra simply may be less likely to eat a lot of artery-clogging foods.

Despite these caveats, however, Patterson and colleagues think their findings warrant further study. "For dietary fat and serum cholesterol, the effect was big enough to overcome the small sample size in terms of statistical significance,&uqot; she says. "In addition, the dietary data in this study corresponded to changes in cholesterol and weight."

The researchers measured diet, weight and serum-cholesterol levels in 335 adults in Indianapolis, the first test market for the fat imposter. Participants were screened with blood tests and dietary questionnaires before olestra was released into the market and again a year later, after olestra-containing foods were widely available.

While heavy olestra intake was associated with lowering LDL, or so-called "bad," cholesterol, it had no effect on HDL, or "good," cholesterol, Patterson says.

Mean dietary fat intake also fell among heavy olestra consumers, from 35 percent daily calories from fat at the beginning of the study, before olestra hit the market, to 32 percent a year later. (Nutrition experts recommend that consumers get 30 percent or less of their daily calories from fat.) Among the heaviest consumers of olestra, there also was a significant decrease in saturated-fat intake. In non-consumers, fat intake overall increased slightly. The effect on weight was less dramatic. Heavy consumers of olestra lost about a pound, while weight remained stable among non-consumers.

While statistically significant, these effects cannot be explained entirely by eating olestra, Patterson cautions, since even the heaviest consumers ate a relatively small amount of the fat substitute. Instead, the researchers attribute the decrease in fat intake, weight and serum cholesterol to a combination of factors, biological and behavioral.

"While there are some plausible biologic reasons for these changes, such as the possibility that olestra sequesters dietary cholesterol in the gut before it has a chance to get to the bloodstream, olestra consumption is probably also an indicator of a healthier lifestyle in general," Patterson says. "Instead of being a marker for bad behavior, we've found it's a marker of good behavior; people who eat olestra tend to exercise more, eat better and be more health-conscious."

This observation is supported by an earlier report by Patterson and colleagues, based on data from the same study population that found people who eat olestra-based snacks strongly believe in a connection between diet and health. For example, olestra consumers are significantly more likely to believe in the importance of eating a low-fat diet and to think about health when selecting foods as compared with those who don't eat the fat substitute.

These health beliefs in turn influence behavior such as diet and exercise. Olestra manufacturer Procter & Gamble Co. commissioned the study, called the Olestra Post-Marketing Surveillance Study, or OPMSS, to meet FDA requirements for post-marketing surveillance of the fat substitute, also known by the brand name Olean.

The overall objective of the study is to find out how many people eat olestra, how much they consume, and whether blood levels of vitamins and carotenoids are affected by the amount of olestra eaten.

The assessment of olestra's impact on cholesterol, fat intake and weight, a spin-off of the larger project, was motivated by Patterson's scientific curiosity.

"When the FDA mandated surveillance of olestra's nutritional impact, we saw that as an opportunity to address, from a public-health standpoint, additional scientific questions, to see what happens when one of these specially manufactured nonfat products becomes available in the marketplace," says Patterson, co-principal investigator of OPMSS. "This is the first study to specifically examine the effects of new fat-modified foods in the U.S. food supply."

Olestra, a synthetic fat substitute made from sucrose and fatty acids, in 1996 gained federal approval for use in savory snacks, in 1997 was test marketed at selected sites and in 1998 became available in stores nationwide. Unlike regular fat, which contains 9 calories per gram, olestra provides zero calories because it is indigestible; its unique molecular structure prevents bodily absorption. While many fat-modified foods are calorically dense, those made with olestra are substantially lower in calories than their full-fat counterparts.

While there's been concern that olestra may interfere with the metabolism of fat-soluble vitamins and carotenoids, preliminary data have shown no statistically significant evidence that it affects serum levels of carotenoids or vitamins A, D and E, regardless of the amount consumed, according to Mark Thornquist, Ph.D., principal investigator of OPMSS.

"With the data to date, we can rule out large nutritional effects of olestra, but we will need data from the full study to determine whether olestra has modest effects," says Thornquist, an associate member of the Hutchinson Center's Public Health Sciences Division. "This is early in the game," Patterson echoes. "When the study is over in 2001, we'll be able to draw some firm conclusions."