Long-term use of the fat substitute, olestra, marketed by Procter and Gamble under the name Olean, may be linked to an increased risk of cancer, stroke and heart disease, according to nutritionist Dr. Walter Willett of Harvard School of Public Health in Boston, Massachusetts.

The issue at hand is not the well-known potential side effects of the product, abdominal cramping and diarrhea. Dr. Willett is more concerned about the people who don't have those side effects because they will continue to consume olestra and suffer long-term consequences. What Willett and other nutrition experts are worried about is what they call the "dramatic" drop in blood levels of some protective vitamins and carotenoids associated with the consumption of even a small serving of olestra.

Willett said in an interview that daily consumption of a 1-ounce serving of olestra has been shown to lower blood carotenoid concentrations by as much as 50% to 70%. Low levels of carotenoids have been associated in various studies with increased rates of coronary heart disease, stroke and myocardial infarction, cancers of the lung, prostate and uterus, and cataracts as well as degenerative changes of the eye that can lead to blindness.

According to the Harvard researcher, the FDA panel that originally granted Procter and Gamble marketing approval for olestra did not contain an expert on carotenoids. Because of this lack, he said the effects of olestra on lowering carotenoid levels were not taken into serious consideration by the panel.

Following FDA approval of olestra 2 years ago, Willett conducted a survey of members of the National Academy of Sciences Expert Committee on Diet, Nutrition and Cancer. When he asked each of these researchers whether they were reasonably certain that the carotenoid lowering due to olestra would not increase cancer risks, there was not a single member who, by the FDA criteria, would have approved olestra.

At a press conference held this week by the Center for Science in the Public Interest, Willett presented estimates that consumption of olestra in the average quantities predicted by Proctor and Gamble would result each year in an additional 2,000 to 9,800 cases of prostate cancer; 32,000 cases of coronary heart disease; 1,400 to 7,400 cases of lung cancer; and 80 to 390 cases of macular degeneration (a disease of the retina that can cause blindness) in the US population. An FDA panel is scheduled to meet June 15-17 to review evidence regarding the safety of olestra.