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Can Walnuts Help to Prevent Colon Cancer?


Daniel W. Rosenberg, PhD

Research suggests that eating walnuts may help to prevent breast and possibly prostate cancers, or slow their progression. Now AICR is funding research on the possibility that walnuts may help ward off colorectal cancer as well.

Studies on prostate and breast cancer have established that something in walnuts, most likely a combination of substances, reduces the initiation of tumors and slows the growth of cancer cells. Research on the effects of walnuts on colorectal cancer has only recently begun, but investigators are already finding promising results there, as well.

Dr. Daniel Rosenberg, Professor of Medicine at the University of Connecticut and an AICR grantee, is studying the effects of walnuts as whole foods on colon cancer in mice.

“It’s important to study whole foods as opposed to extracts,” Dr. Rosenberg explains, “because evidence suggests that a synergistic combination of substances gives walnuts their cancer-fighting ability.” Synergy occurs when the effect of two or more substances is equal to more than the sum of each individually.

Walnuts contain omega-3 fatty acids and seem to reduce inflammation, a condition that has been linked to increased cancer risk. Another AICR-funded study found that walnuts may help to inhibit the growth of prostate cancer tumors in mice, a result that agreed with earlier studies on breast cancer.

A Larger Picture?

However, in all of these studies the omega-3 fatty acids alone could not account for walnut’s cancer-fighting effects. Other substances, perhaps acting together, are likely to be involved. Among them are:

  • the phytochemical ellagic acid;
  • the mineral selenium;
  • the antioxidant melatonin;
  • molecules called phytosterols; and
  • dietary fiber

Investigators believe that a combination of two or more of these substances could be responsible for the observation that whole walnuts may reduce the growth rate of breast and prostate tumors.

For colon cancer, research is still in a very early stage. Dr. Rosenberg’s studies involve mice that have been induced to develop colon tumors in ways that mimic its natural development in humans:

  1. Using mice who develop slowly-growing colon cancer, the researchers are finding a way to modify the mice’s diet with walnuts while not increasing their calories and making them obese.
  2. Developing a procedure to use in the mice that induces genetic mutations identified from biopsies of human colon cancers and are found to be related to development of colon cancer.
  3. Dr. Rosenberg and his group have found a way to induce something akin to ulcerative colitis in the mice. The animals will be given walnuts to see if the inflammatory pathway known to convert ulcerative colitis into colon cancer will be affected.

“I believe this part of our study has the greatest chance for producing information we can use to help human patients,” Dr. Rosenberg says. “Any promising leads could be studied directly by adding walnuts to the diets of the large group of patients currently enrolled in a colon biopsy study at the University of Connecticut,” he adds.

No. 127, Spring 2015

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