Modified citrus pectin (MCP) is a soluble fiber that has been processed in such a way that it can be absorbed - and as a supplement, has been promoted for "detoxification," "cellular health," and preventing or slowing cancer growth such as in prostate and breast cancer tumors.
In-vitro and animal studies suggest that MCP may slow the growth of certain cancer cells, including human prostate cancer cells (Yan, Integr Cancer Ther 2010; Glinsky, Carbohydr Res 2009; Nangia-Makker, J Natl Cancer Inst 2002). However, there have been only two clinical studies on the effects of MCP in men with prostate cancer and neither study included a control group or placebo, making the results questionable.
One small clinical trial of 10 men with prostate cancer who were given MCP after traditional treatments failed (radical prostatectomy, radiation or cryosurgery) found that a daily dose of 14.4 g (6 capsules containing 800 mg Pecta-Sol® taken three times per day) for 12 months significantly slowed the rate at which prostate antigen (PSA) levels increased in the blood (Guess, Prostate Cancer Prostatic Dis 2003). (There is a higher risk of death when PSA levels rise rapidly, such as doubling in just three months. A slower rise, such as a doubling over one to 10 years, is associated with local rather than systemic recurrence (Tollefson, Mayo Clin Proc 2007)).
A second clinical study in Germany found that among 29 men and women with various advanced solid cancerous tumors (including 10 men with prostate cancer tumors) who took 5 grams of MCP powder (mixed with water and juice three times per day) for two to four months, an overall clinical response associated with a stabilization and/or improvement in measures of quality of life, such as fatigue, pain, and appetite was reported. The study also included individuals with breast, colorectal, liver, pancreatic and cervical cancer (Azemar, Clin Med Insights Oncol 2007).
Similarly, evidence that MCP may be beneficial for slowing breast cancer growth is very preliminary. The study above that found MCP improved certain measures of quality of life in men and women with various types of cancer included five patients with advanced solid breast cancer tumors, although results were reported for the whole group, not by specific types of cancer, and the study did not a control group or placebo, which is necessary to show that a treatment is effective (Azemar, Clin Med Insights Oncol 2007). The only other evidence appears to be a study in mice injected with human breast cancer cells found that MCP given orally slowed breast tumor growth (Nangia-Makker, J Natl Cancer Inst 2002).
The Susan G. Komen foundation for breast cancer notes "Modified citrus pectin is still considered an experimental therapy for cancer and should be used as an adjuvant to standard cancer therapy under medical supervision."
Modified citrus pectin is generally well-tolerated, although mild gastric upset, gas and diarrhea have been reported. In a study among people with cancer, the most commonly reported side effects were itching, upset stomach and gas; one individual with liver cancer stopped supplementation due to increased itching (Azemar, Clin Med Insights Oncol 2007).
Pectasol® and PectaSol-C® are the commonly sold brands of modified citrus pectin powders which have been used in clinical studies, with similar recommended dosages as used in these studies — 5 grams three times per day. Capsules are available and may be more convenient to carry but generally contain 1 gram or less, so about 6 capsules per serving would be required.
The bottom line:
Preliminary evidence suggests modified citrus pectin may slow the growth of cancerous cells or improve quality of life measures in individuals with prostate or breast cancer, but use of MCP is still considered experimental. Larger, placebo-controlled studies are needed. It is general well-tolerated, although itching, upset stomach, gas, cramping and diarrhea have been reported. Look for supplements containing Pectasol® and PectaSol-C®, which have been used in clinical studies. (See our Where to Buy page for our list of retailers that sell modified citrus pectin that we've found to be reputable.)
For information on other supplements for prostate cancer, see the Green Tea Review, and for more about supplements that may treat non-cancerous prostate symptoms, see the Saw Palmetto Review.