Researchers from the School of Medicine at the University of Texas Health Science Center San Antonio and colleagues examined whether a walnut diet would reduce the development and growth of human prostate cancer cells (LNCaP) in nude mice.

Previous studies had shown that consuming walnuts on a regular basis did not influence serum prostate-specific antigen (PSA) levels but itdid improve biomarkers of prostate health in normal men.

Dr. Elaine Hardman, PhD, Associate Professor, Biochemistry and Microbiology, Marshall University in 2011, while Dr. Hardman was at the Joan C. Edwards School of Medicine at Marshall University and colleaguesin a study had compared the effects of a typical diet and a walnut enriched diet across the lifespan: through the mother from conception through weaning, and then through eating the food directly. The amount of walnut in the test diet equates to about 2 ounces a day for humans. The results showed the risk of breast cancer dropped significantly in mice that had been fed the walnut enriched diet. Dr. Hardman is co-author of this current study.

“Considering the findings of Hardman and coworkers documenting that a walnut-enriched diet inhibited the initiation and progression of two types of experimental mammary cancer, we deemed it important to test whether the same diet would influence the growth of prostate cancer xenografts growing in male nude mice,” write the researches in their introduction.

In this new study Dr. Russel Reiter, Ph.D., professor of cellular and structural biology at the Health Science Center and study’s senior’s author along with colleagues had purchased 48 immuno-compromised nude mice, six weeks old from Harlan Labs. The mice had been housed four page cage. After a two week period of adjustment, 32 mice had been given a control diet and 16 mice had received a walnut enriched diet.

The results had showed the walnut enriched diet reduced the number of tumors and growth; three of the sixteen mice (18.7%) of the walnut fed mice developed tumors, 14 of the 32 mice (44%) of the control fed mice developed tumors. The tumors had developed more slowly in the walnut fed mice compared to the control mice. The final average tumor size in the walnut-diet animals was roughly one-fourth the average size of the prostate tumors in the mice that ate the control diet.

The mice consumed a diet typically used in animal studies, except with the addition of a small amount of walnuts pulverized into a fine powder to prevent the rodents from only eating the walnuts. “The walnut portion was not a large percentage of the diet,” Dr. Reiter said. “It was the equivalent to a human eating about 2 ounces, or two handfuls, a day, which is not a lot of walnuts.”

In closing Dr. Reiter stated “We found the results to be stunning because there were so few tumors in animals consuming the walnuts and these tumors grew much more slowly than in the other animals.” “We were absolutely surprised by how highly effective the walnut diet was in terms of inhibition of human prostate cancer.”

“The data to date suggest that using walnuts on a regular basis in the diet may be beneficial to defer, prevent or delay some types of cancer, including breast and prostate.”

This study appears in the journal Cancer Investigation.