fiber and Cholesterol

Does fiber lower cholesterol?

Pawel Malczewski
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Short summary

Soluble fiber reduces total and LDL cholesterol by a small amount. However,  in the context of reducing the risk of cardiovascular diseases, soluble fiber has other, more significant functions. For a quick answer click here.

Explanation

Studies show that soluble fiber reduces cholesterol

Various studies show that soluble fiber, from sources as oats, psyllium and pectin, can reduce total and LDL (Low-density lipoprotein) cholesterol by a small amount.

A large meta-analysis of 67 studies and 2990 participants has shown a significant decrease in total cholesterol in 60-70% of all the trials. The results were similar for all types of soluble fiber: (1)Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999 Jan;69(1):30-42. Available here. (2)Davy B, Davy K, Ho RC, Beske SD, Davrath LR, Melby CL. High-fiber oat cereal compared with wheat cereal consumption favorably alters LDL-cholesterol subclass and particle numbers in middle-aged and older men. Am J Clin Nutr August 2002 vol. 76 no. 2 351-358 . Available here. (3)Lamarche B, Desroches S, Jenkins DJA, Kendall CWC, Marchie A, Foulkner D, et al. Combined effects of a dietary portfolio of plant sterols, vegetable protein, viscous fibre and almonds on LDL particle size. British Journal of Nutrition / Volume 92 / Issue 04 / October 2004, pp 657-663. Available here.

  • soluble fiber reduces total and LDL cholesterol irrespective whether one has very high cholesterol (hypercholesterolemia >6.2mmol/L or >240mg/dL) or lower cholesterol concentrations;
  • a practical dosage of 1-10 g daily of soluble fiber can decrease LDL and total cholesterol by approximately 1%-2%;
  • dietary fiber has an insignificant effect on the change in HDL (known as “good”) cholesterol;
  • soluble fiber, that has viscous properties from oatmeal, reduces LDL cholesterol, including small, dense LDL cholesterol which is one of the risk factors in Cardiovascular Disease (CDV).

How does it work?

The mechanism of cholesterol reduction it is still unknown. There are, however, several hypotheses: (4)Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999 Jan;69(1):30-42. Available here.

  • soluble fibers bind cholesterol and bile acids and remove cholesterol in the stool;
  • up-regulation of cholesterol receptors. Lower cholesterol levels in the cells leads to cells producing more receptors on its surface to be able to capture more cholesterol. That increase in receptors is call up-regulation;
  • fermentation process of fibers produces short-chain fatty acids which has shown to inhibit cholesterol production in rats;
  • presence of fiber improves intestinal contractions;
  • highly viscous fiber diet slows down the absorption of macronutrients which improves insulin sensitivity;
  • lowers the overall energy intake from diet due to increased satiety.

Fiber in the cardiovascular disease context

Fiber reduces CDV risk not only by its small contribution in the reduction of cholesterol. Here are some points to consider: (5)Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999 Jan;69(1):30-42. Available here. (6)Ma Y, Griffith JA, Chasan-Taber L, Olendzki BC, Jackson E, Stanek EJ, et al. Association between dietary fiber and serum C-reactive protein. Am J Clin Nutr April 2006 vol. 83 no. 4 760-766. Available here.

  • LDL cholesterol consists of small, dense cholesterol and large cholesterol. Only the dense cholesterol particles are a risk factor in CDV. This means that the Total Cholesterol and LDL cholesterol tests currently used are not good indicators for CDV risk. (read more..)
  • The studies mentioned above show a reduction of small, dense types as a part of LDLs. As the reduction of LDLs was 1-2%, this means that the reduction of their small, dense fraction will be even smaller.
  • High HDL “good cholesterol” is associated with lower risk of CDV but fiber does not seem to change the amount of HDL in the blood significantly.
  • Dietary fiber protects against high C-reactive protein (CRP) which is an inflammatory indicator and another risk factor of CDV.
  • Viscous fiber contributes to weight loss and reduces the risk of CDV. (read more..)

Conclusion

Back to top

There is a good amount of evidence that soluble fiber reduces the total and LDL cholesterol by a small amount.
Although the reduction is small and only relevant for LDL particles, fiber exerts other actions reducing the risk of CDV, which in the context of the myth question is important.
These actions are: reduction of inflammation, weight loss, lowering of blood glucose and insulin and reduction of blood pressure through the action of potassium and magnesium contained in fiber rich foods.

Even though the direct answer to the myth question (that fiber reduces cholesterol by a small fraction) may not convince you, when used in the context in which this question is used, fiber is a very useful component of our diet and reduces the risk of CVD via many actions in the body.

References   [ + ]

1. Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999 Jan;69(1):30-42. Available here.
2. Davy B, Davy K, Ho RC, Beske SD, Davrath LR, Melby CL. High-fiber oat cereal compared with wheat cereal consumption favorably alters LDL-cholesterol subclass and particle numbers in middle-aged and older men. Am J Clin Nutr August 2002 vol. 76 no. 2 351-358 . Available here.
3. Lamarche B, Desroches S, Jenkins DJA, Kendall CWC, Marchie A, Foulkner D, et al. Combined effects of a dietary portfolio of plant sterols, vegetable protein, viscous fibre and almonds on LDL particle size. British Journal of Nutrition / Volume 92 / Issue 04 / October 2004, pp 657-663. Available here.
4. Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999 Jan;69(1):30-42. Available here.
5. Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999 Jan;69(1):30-42. Available here.
6. Ma Y, Griffith JA, Chasan-Taber L, Olendzki BC, Jackson E, Stanek EJ, et al. Association between dietary fiber and serum C-reactive protein. Am J Clin Nutr April 2006 vol. 83 no. 4 760-766. Available here.

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