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May 8, 2015 | 3 minute read

In Animals, Walnut Diet Targets Colon Tumor’s microRNA, Slows Tumor Growth

Study reveals new mechanism by which diet may play a role in reducing inflammation and cancer risk

WASHINGTON, DC — A new study conducted in mice finds that daily walnut consumption slows colon tumor growth while affecting genetic molecules in the tumor that play a role in gene expression.

The research offers insights into how diet in general, and walnut’s omega-3 fats in particular, may affect cancer risk by targeting micro-RNAs (miRNAs), small non-coding chunks of RNAs that appear to play a role in cell development and cell death (apoptosis).

The study, led by Christos S. Mantzoros, MD, DSc, PhD, Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, was published in The Journal of Nutritional Biochemistry. It was funded by the American Institute for Cancer Research and the California Walnut Commission.

Previous research has suggested that nutrients and phytochemicals may influence the expression of miRNA in cancer cells. This study also builds on research by the same group that suggests walnuts play a protective role in colon cancer. Walnuts contain the omega-3 fatty acid known as alpha-linolenic acid (ALA), along with other phytochemicals and vitamins that are studied for their role in health and cancer protection.

In the study, mice were randomized into one of two diet groups. One group consumed ground walnuts, equal to approximately two servings per day for humans. The control group consumed a similar diet, with corn oil in place of walnut fats.

After 25 days on the diets, colorectal tumors were smaller in the walnut-consuming mice compared to the control group. The tumors of the walnut-consuming mice had 10 times the amount of total omega-3 fatty acids, including ALA, compared to the control group. Smaller tumor size was associated with a greater percentage of omega-3s in tumor tissues.

Analysis found that tumors from the walnut-fed mice showed different miRNA expression levels for a number of the molecules than tumors from the control mice, suggesting a dietary influence. There are several ways in which miRNA may regulate cancer development, says Mantzoros, such as influencing apoptosis, cell invasion, migration, and proliferation.

Many human studies have shown that diet can reduce risk for many cancers. This animal study is not directly applicable to people, but its findings advance researchers’ understanding of the mechanisms underlying colon cancer development and growth. They also provide novel prevention, diagnostic and therapeutic opportunities to be tested in humans at a later stage, says Mantzoros.

Colorectal cancer is the third leading cancer diagnosed in the United States, aside from skin cancers. AICR estimates that half of US colorectal cancer cases can be prevented with diet, physical activity, and staying a healthy weight.

Notes/References for editors

  • Tsoukas MA, Ko BJ, Witte TR, Dincer F, Hardman WE, Mantzoros CS. “Dietary walnut suppression of colorectal cancer in mice: Mediation by miRNA patterns and fatty acid incorporation. J Nutr Biochem. 2015 Apr 1. [Epub ahead of print] http://dx.doi.org/10.1016/j.jnutbio.2015.02.009
  • AICR’s  Colorectal Cancer CUP report found that risk of this cancer increases with obesity, alcohol, and high amounts of red and processed meats; risk decreases with physical activity and foods containing fiber.

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