The trial data, published in the journal Cancer Investigation, investigated whether a walnut-enriched diet had benefits over a non-enriched diet in a mouse model of human prostate cancer after previous findings suggested that walnuts had a beneficial effect on breast cancer.
Led by Professor Russel Reiter from The University of Texas, the researchers found that only 18% of mice fed the walnut-enriched diet developed prostate tumours while 44% developed them when fed a control diet.
"We found the results to be stunning because there were so few tumours in animals consuming the walnuts and these tumours grew much more slowly than in the other animals," said Reiter.
"We were absolutely surprised by how highly effective the walnut diet was in terms of inhibition of human prostate cancer."
Study details
The team injected immune-deficient mice with human prostate cancer cells that typically cause tumours to start growing within three to four weeks. The mice consumed a diet typically used in animal studies, with the mice split into groups that received either a walnut-enriched diet (16 mice) or a non-walnut control diet (32 mice).
"The walnut portion was not a large percentage of the diet," 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."
The team reported that three of 16 mice (18%) eating the walnut-enriched diet developed prostate tumours, compared with 14 of 32 mice (44%) on the non-walnut control diet.
In addition final average tumour size in the walnut-fed animals was roughly a quarter of the average size of the prostate tumours that developed in the mice eating the control diet, said Reiter and his colleagues.
"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," commented Reiter.
The authors reported no conflicts of interest - adding that the work was supported by a grant from the American Institute for Cancer Research (grant #09A073).
Source: Cancer Investigation
Vol. 31, No. 6 , Pages 365-373, doi: 10.3109/07357907.2013.800095
"A Walnut-Enriched Diet Reduces the Growth of LNCaP Human Prostate Cancer Xenografts in Nude Mice"
Authors: Russel J. Reiter, Dun-Xian Tan, Lucien C. Manchester, et al