Nutrition Hotline
REED MANGELS, PhD, RD
This issue's Nutrition Hotline discusses what plant sterols are, what effects they can have on one's diet, and which foods are good sources for them.
QUESTION: "I've recently noticed that some foods on the shelves at my grocery store contain plant
sterols. What are plant sterols, and are they vegetarian? Why are they being added to foods? Do vegetarians and
vegans need to buy fortified foods to get plant sterols?"
C.S., MD
ANSWER: Plant sterols are very similar in structure to cholesterol. Plant sterols are found in plants, while cholesterol is found in humans and other animals. Although we often think of cholesterol as something bad, every membrane in our bodies contains cholesterol. Cholesterol has many roles, including making it possible for our brains to function properly, producing hormones, and helping to produce the bile acids that enable us to digest fat.
Since cholesterol has so many important functions, our bodies make enough cholesterol to meet our needs, and we don't need to get any from our diets. We typically produce approximately 1,000 milligrams of cholesterol every day, more than is found in most diets. Some people make too much cholesterol or regularly eat foods high in cholesterol, leading to elevated blood cholesterol levels and an increased risk of heart disease.
In the same way that our membranes contain cholesterol, the membranes of plants contain plant sterols, also called phytosterols. Plant sterols are different enough from cholesterol that they are not well absorbed by humans.
Consuming plant sterols seems to reduce how much cholesterol we absorb. In other words, if you eat a meal containing plant sterols, you won't absorb as much cholesterol at that meal as you usually would. This has the effect of reducing blood cholesterol levels. Over time, eating around 2,000 milligrams (2 grams) of plant sterols daily can lower blood cholesterol levels about 10 percent.1
You may be thinking, "Wait a minute. I'm vegan. I don't have any cholesterol in my diet." Even if you don't eat any foods containing cholesterol, your body reabsorbs cholesterol from intestinal secretions every day. So, if you don't reabsorb some of this cholesterol because you're eating plant sterols, your body will have less cholesterol to deal with.
The best results, in terms of lowering blood cholesterol levels, from plant sterols are seen in people with very high blood cholesterol levels. They have been shown to be effective in people with slightly or moderately high blood cholesterol levels as well.
Plant sterols are found in, well, plants. Some plant-based foods have more plant sterols than others, however. Especially good sources include oils like corn oil and canola oil. Broccoli, almonds, pistachios, and wheat germ are other foods that contain generous amounts of plant sterols, although other fruits, vegetables, nuts, and grains also supply plant sterols. Most studies have found that a plant sterol intake of approximately 2,000 milligrams daily is useful in controlling blood cholesterol levels. However, even increasing your usual intake of plant sterols by as little as 200 milligrams could lead to a 3 percent decrease in blood cholesterol levels.2 According to the American Heart Association, it seems that no additional benefits are gained by getting more than approximately 2,000 milligrams of plant sterols daily.3
Americans are notorious for not eating generous amounts of foods that provide plant sterols. That's why the average American's intake is around 250 milligrams per day. Vegetarians do better, averaging almost twice as much, approximately 500 milligrams.4 The plant sterol intake of vegans has not been studied but is likely to be even higher.
Food manufacturers have begun adding plant sterols to some foods like margarine, orange juice, rice milk, and cheese in an attempt to increase consumers' intake of plant sterols (and to sell their products). The plant sterols that are added to foods are plant-based—made from soy, corn, and other plants—and, therefore, are suitable for vegetarians, including vegans. Not all foods to which plant sterols are added are vegetarian.
You'll have to decide for yourself whether you want to purchase products fortified with plant sterols. It is a challenge to get more than 500-1,000 milligrams of plant sterols daily from diet alone without using fortified foods. For many people, even 500-1,000 milligrams of plant sterols from diet alone will be enough. People with high blood cholesterol levels, especially those with high LDL cholesterol levels, who are already eating a heart-healthy diet may opt to add more plant sterolsfrom fortified foods to see if they can help lower blood cholesterol levels.
Plant sterols are just one part of a heart-healthy diet. Many other factors are also important, such as eating a diet low in saturated fats and trans fats, free of cholesterol, and high in fiber. Even for people eating a vegan or near-vegan diet, adding foods like soy products, nuts, and foods high in soluble fiber (like oats, barley, psyllium, eggplant, and okra), along with plant sterols, can reduce blood levels of LDL cholesterol even more than just plant sterols would by themselves.5 In other words, plant sterols can be helpful, but they don't take the place of eating sensibly and exercising.
REFERENCES
- 1 Katan MB, Grundy SM, Jones P, et al. 2003. Efficacy and safety of plant stanols and sterols in the management of blood cholesterol levels. Mayo Clin Proc 78:965-78.
- 2 Ellegard LH, Andersson SW, Normen L, et al. 2007. Dietary plant sterols and cholesterol metabolism. Nutr Rev 65:39-45.
- 3 Lichtenstein AH, Appel LJ, Brands M, et al. 2006. Diet and lifestyle recommendations revision 2006: a scientific statement from the American Heart Association Nutrition Committee. Circulation 114:82-96.
- 4 Ling WH, Jones PJ. 1995. Dietary phytosterols: a review of metabolism, benefits and side effects. Life Sci 57:195-206.
- 5 Jenkins DJA, Kendall CWC, Faulkner DA, et al. 2006. Assessment of the longer-term effects of a dietary portfolio of cholesterol-lowering foods in hypercholesterolemia. Am J Clin Nutr 83:582-91.
