A reader recently asked if eating a significant amount of fiber can diminish the effect of Lipitor (atorvastatin) in reducing cholesterol levels. I am not aware of any negative effect of fiber on the absorption or the effects of the statins on lowering cholesterol. Statins including Lipitor can cause gastrointestinal side effects such as diarrhea and interestingly, constipation as well. The mechanism is not completely understood. What I am quite aware of is the overall positive effects of fiber in improving cholesterol levels including evidence to support that fiber can enhance a statin's effectiveness.
Fiber can improve cholesterol levels in several ways. One often overlooked benefit of eating fiber is that it can easily act as a substitute for a potential damaging food. For example, we know that we should minimize the intake of trans and saturated fats. But, we still need to eat something to satisfy our hunger as well as give us our daily supply of energy. If we substitute carbohydrates for fats, we may lower LDL but also may raise triglycerides and lower HDL. If, however, we substitute these bad fats with fiber, then we can get the full benefit of a heart healthy diet.
Certain soluble fibers such as psyllium, oat products, pectin, and guar gum can directly lower LDL. How fiber exerts this effect is not fully known. Some possible effects of fiber include binding to cholesterol. in the intestine in the form of bile acids (a cholesterol rich acid excreted by the liver into the intestine to aid in the digestion of fat), changing intestinal movement thereby lowering cholesterol and fat absorption, and directly inhibiting liver production of blood cholesterol by increasing production of intestinal bile acids. Regardless of the how it does it, fiber is good for your cholesterol. And even more importantly, eating fiber has been shown to reduce the risk of heart disease.
What's the downside? You really have to want to eat fiber to make a significant impact. If you eat 3 bowls of oatmeal or 3 apples per day, you can expect to lower your cholesterol by 2%. If your cholesterol level is 240mg/dl then expect fiber to lower it by a mere 4-5 points. You still have a long way to go to achieve your target cholesterol of less than 200mg/dl. But, any benefit is a good thing. That 2% reduction in your cholesterol may translate into a 4% reduction in the risk of developing significant heart disease.
Lastly, as I mentioned in my answer to the reader, I am not aware of any negative effects of fiber on statins. I do know that there is some evidence to support that fiber can supplement the effect of statins. One study in particular looked at taking low dose simvastatin (zocor) @ 10mg/day with 15grams of psyllium vs. double the dose of simvastatin @ 20mg and no requirement of fiber intake. The end result was that the 2 treatment strategies achieved the same cholesterol and LDL reduction.
In summary, fiber is good for cholesterol as well as for preventing other medical illnesses such as diabetes and colon cancer. We should be eating about 20-30grams of fiber per day, but most of us come up short. Some good sources of fiber besides supplemental powders, capsules, and bars include certain high fiber cereals (ie. All Bran by Kelloggs), dates, prunes, raspberries, and peas. One main obstacle in achieving our dietary fiber goal is taste. We prefer to eat sweet or fatty foods as opposed to Cheerios or brown rice. However, as a dietician once told me, we are eating to live, and not necessarily living to eat. What we choose from the menu is up to us.
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