Eating a modest amount of walnuts can protect against prostate cancer, a new study has claimed.
Researchers from the School of Medicine at The University of Texas Health Science Center at San Antonio injected immune-deficient mice with human prostate cancer cells.
Within three to four weeks, tumours typically started to grow in a large number of these mice. The study asked whether a walnut-enriched diet versus a non-walnut diet would be associated with reduced cancer formation. A previous study found this to be true for breast cancer.
The study found that three of 16 mice (18 per cent) eating the walnut-enriched diet developed prostate tumours, compared with 14 of 32 mice (44 per cent) on the non-walnut control diet.
Also, the final average tumour size in the walnut-fed animals was roughly one-fourth the average size of the prostate tumours that developed in the mice eating the 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 study senior author Russel Reiter, professor of cellular and structural biology at the Health Science Center.
"We were absolutely surprised by how highly effective the walnut diet was in terms of inhibition of human prostate cancer," Reiter said.
The mice consumed a diet typically used in animal studies, except with the addition of a small amount of walnuts pulverised into a fine powder to prevent the rodents from only eating the walnuts.
"The walnut portion was not a large percentage of the diet. It was the equivalent to a human eating about 2 ounces, or two handfuls, a day, which is not a lot of walnuts," Reiter said.
Study co-author W Elaine Hardman, of the Joan C Edwards School of Medicine at Marshall University, had published a study in 2011 that showed fewer and smaller tumours among walnut-fed mice injected with human breast cancer cells.
"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," Reiter said.