Two Ounces of Walnuts a Day Can Slow Growth of Cancer

It’s time to bring back Waldorf Salad — that delicious salad of chopped apples, grapes, celery, watercress and walnuts. A new study, funded partly by the American Institute for Cancer Research, has demonstrated that walnuts suppress the development of breast cancer tumors in mice.

What is so special about walnuts? I asked W. Elaine Hardman, PhD, associate professor of biochemistry and microbiology at Marshall University School of Medicine in Huntington, West Virginia, the study’s lead author. “Of all the common nuts, walnuts contain the highest amount of omega-3 fatty acids,” she told me. Walnuts also have significant amounts of antioxidants and phytosterols, compounds that have been shown to individually slow cancer growth.

To see if the dietary addition of walnuts would impact cancerous tumors, Dr. Hardman tested 40 female mice that had been implanted with cells of human breast cancer tumors. Once the tumors reached 3 mm to 5 mm in diameter, half the mice stayed on their standard mouse diet, while the other half ate a diet adjusted to include ground English walnuts, the human equivalent of two ounces per day. Within 35 days, growth of breast cancer tumors in the walnut-fed mice had slowed to the extent they were half the size of the tumors in the non-walnut fed mice. “We were all surprised that the study came out that well,” says Dr. Hardman. The team hadn’t expected that adding such a small amount to the diet would be enough to suppress the growth as much as it did.


  • If walnuts help suppress breast cancer tumors, it’s likely they will also impact other hormonally driven cancers, such as prostate cancer.
  • Walnuts seem to also work to prevent (or at least delay) the onset and proliferation of cancerous tumors. A new study presented at the annual meeting of the American Association for Cancer Research in April reported that walnuts at the same dose as the first study reduced incidence, multiplicity and growth rate of mammary gland cancers in the mice by about 50%.
  • Dr. Hardman knows of no supplement that replicates all the compounds, oils and acids in walnuts. Best to eat the real thing, and don’t forget to include the brown paper thin skin too.
  • One walnut is about 24 calories. Two ounces a day (or 14 walnuts) is 370 calories. The good news is that walnuts are a very satiating snack, Dr. Hardman says, and neither the people nor mice in the studies gained weight when they snacked upon them.