Are Sterol Esters the Next "Trans Fat"?
See that container of yogurt?
It contains 600 mg of plant sterols that help reduce cholesterol. It even says "heart healthy" . . . but is it?
"Trans" fats all over again?
Back in the 1970s, we were all warned to reduce the saturated fat in our diet. Food manufacturers helped us comply with this advice by developing hydrogenated, or "trans," fats, to replace saturated fats in margarine and all varieties of processed foods.
Fast forward to the 1990s, and it turns out that hydrogenated fats are worse than saturated fatsâ”€increase LDL cholesterol, reduce HDL, increase inflammation, increase risk for cancer. These man-made fatty acids proved to be among the biggest nutritional mistakes of the 20th century.
But I worry there is yet another substance that is working its way into the American processed food cornucopia that has potential for repeating the trans fat debacle: sterol esters.
What are sterols?
Sterols are naturally-occurring oils found in vegetables, nuts, and other foods in small quantities. Most of us ingest 200-400 milligrams per day just by eating plant-sourced foods.
The chemical structure of sterols is similar to human cholesterol (differing at one carbon atom). When taken orally, sterols block intestinal absorption of cholesterol and have therefore been used to reduce blood levels of total and LDL cholesterol.
Take Control ® butter substitute, first released during the late 1990s, was the first commercial sterol-containing product marketed to reduce cholesterol when 2-3 tbsp are used daily, providing 3400 - 5100 mg of sterols. Several clinical trials have conclusively confirmed that these products reduce cholesterol levels.
There are now hundreds of products that have sterol esters added to them, such as orange juice, mayonnaise, yogurt, breakfast cereals, even nutritional supplements. Most of these products proudly bear "heart healthy" claims. They do indeed perform as advertised: Add sterols to your daily diet and LDL cholesterol is reduced by about 10-15%.
Problem: What happens when sterols are absorbed from the intestine and get into the bloodstream?
Some insight can be gained by looking at a condition called sitosterolemia, a rare (1 person per million) genetic disorder that permits absorption of sterols from the intestine. While you and I absorb <10% of sterols ingested, people with sitosterolemia absorb sterols more efficiently, resulting in high blood levels of sterols. This results in coronary disease, with heart attacks occurring as young as late teens or 20s. Treatments to block sterol absorption are used to treat these people.
Most of us lack this genetic condition, of course. But if you and I take in 10-20 times greater amounts of sterol esters, do our blood levels of sterols also increase?
Several studies now suggest that, yes, sterol blood levels increase with sterol ingestion. The STRIP Study from Finland showed that children who had double usual sterol intake increased blood levels by around 50%. Another study showed that postmenopausal women with coronary disease had 21% higher levels of sterols than women without coronary disease. The PROCAM and MONICA studies both showed higher blood levels of sterols in people with heart attacks or death from heart disease.
All in all, emerging data suggest that, **when sterols enter the blood, even in tiny amounts, the risk for heart disease may be substantially increased. **
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. 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.)