By now, I'm sure you're well-acquainted with the hydrogenated, trans fat issue.
Hydrogenation of polyunsaturated oils was a popular practice (and still is) since the 1960s, as food manufacturers sought a substitute for saturated fat. Bubbling high-pressure hydrogen through oils like cottonseed, soybean, and corn generates trans fatty acids. These man-made fatty acids, while safe in initial safety testing, proved to be among the biggest nutritional mistakes of the 20th century.
Trans fatty acids have been associated with increased LDL cholesterol, reduction in HDL, oxidative reactions, abnormal rigidity when incorporated into cell membranes, and cancer. Trans fats still dominate many processed foods like chips, cookies, non-dairy creamers, food mixes, and thousands of others. They're also found prominently in fast foods.
Fast forward to today, and most Americans have become aware of the dangers of trans fats and many try to avoid them.
But I worry there is yet another substance that has worked its way into the American processed food cornucopia that has some potential for repeating the trans fat debacle: sterol esters . 
Sterols are naturally-occurring oils found in vegetables, nuts, and numerous other foods in small quantities. Most of us take in 200-400 milligrams per day just by eating plant-sourced foods.
Curiously, the chemical structure of sterols are very similar to human cholesterol (differing at one carbon atom). Sterols, by not fully understood means, block the intestinal absorption of cholesterol. Thus, sterol esters, as well as the similar stanol esters, have been used to reduce blood levels of total and LDL cholesterol.
So far, so good.
The initial commercial products, released in the late 1990s, were Take Control (sterol) and Benecol (stanol), both of which were marketed to reduce cholesterol when 2-3 tbsp are used daily, providing 3400 – 5100 mg of sterol or stanol esters, about 10- to 20-fold more than we normally obtain from foods. Several clinical trials have conclusively confirmed that these products reduce cholesterol levels.
They do indeed perform as advertised. Add either product to your daily diet and LDL cholesterol is reduced by about 10-15%. In fact, in the original Track Your Plaque book, these products were advocated as a supplemental means of reducing LDL when other methods fell short.
In 2008, there are now hundreds of products that have additional quantities of sterol esters in them, such as orange juice, mayonnaise, yogurt, breakfast cereals, even nutritional supplements. Most of these products proudly bear claims like "heart healthy." Stanol esters have not enjoyed the same widespread application. (I believe there may be patent issues or other considerations. However, it's the sterols that are the principal topic here, not stanols.)
Now, here's where it gets a bit tricky. There is a rare (1 per million) disease called sitosterol emia , a genetic disorder that permits the afflicted to absorb more than the usual quantity of sterols from the intestine. While you and I obtain some amount of sterols from plant-based foods, absorption is poor, and we absorb <10% of sterols ingested. However, people with sitosterolemia absorb sterols far more efficiently, resulting in high blood levels of sterols that result in coronary disease and aortic valve disease, with heart attacks occurring as young as late teens or 20s. Treatment to block sterol absorption are used to treat these people.
There are also a larger number, though still uncommon (1/500) of people who have only one of the two genes that young people with sitosterolemia have. These people may have an intermediate capacity for sterol absorption.
Okay, so what does this have to do with you? Well, if you and I now take in 10-20 times greater amounts of sterol esters, do our blood levels of sterols increase?
Several studies now suggest that, yes, sterol blood levels increase with sterol ingestion. One study from Finland, the STRIP Study, showed that children who had double usual sterol intake increased blood levels by around 50% .
Similarly, a Johns Hopkins study in adults with only one of the genes ("heterozygotes") for sitosterolemia increased sterol blood levels by between 54-116% by ingesting 2200 mg of sterols added per day, despite reduction of LDL cholesterol levels.
Even people with neither gene for sitosterol hyperabsorption can increase their blood levels of sterols. But the crucial question: Do the blood levels of sterols that occur in unaffected people or in heterozygotes increase the risk of coronary heart disease? The answer is not known.
Despite the several clinical trials performed with sterol esters, all of them have examined LDL and total cholesterol reduction as endpoints, not cardiovascular events. It is conceivable that, while sterol esters reduce cholesterol, risk for heart disease is increased due to higher blood levels of sterols.
The question is not settled. For now, it is just a suspicion. But that's enough for me to steer clear of processed foods supplemented with these uncertain sterol esters. My previous recommendations for sterol ester products will be removed with the next edition of Track Your Plaque. Until we have solid evidence that there are no adverse cardiovascular effects of sterol esters, in my view they should not be part of anyone's heart-disease prevention program.
(The same argument does not seem to apply to stanol esters, such as that contained in butter-substitute Benecol, since stanol esters are not absorbed at all and remain confined to the intestine.)