WASHINGTON, DC -- Research funded by the American Institute for Cancer Research (AICR) has found evidence that a daily dose of walnuts – equal to two servings a day in humans – reduces the growth of breast cancer tumors in mice. The study is the first to investigate the effect of walnut consumption on cancer.
“This is an intriguing finding that needs to be repeated, and ultimately confirmed in humans,” said Karen Collins, M.S., R.D., Nutrition Advisor for AICR. “But it fits with some of what we’ve seen from other studies. We know that walnuts have a lot to offer, such as omega-3 fat, vitamin E, and other antioxidants. Many of these substances have already shown anti-cancer potential individually.”
Walnuts in the Diet Slow Tumor Growth
In the study, researchers looked at the ability of walnuts to slow the growth of breast tumors using an amount comparable to what humans might eat.
A group of 22 mice with human breast cancer tumors was divided into two groups. One group was fed ground walnuts daily in the amount equivalent to two ounces (28 walnut halves) for humans. The comparison group consumed a diet supplemented with corn oil, along with amounts of vitamins, minerals and fiber that were similar to the amounts occurring in the walnut diet.
After 35 days, the breast cancer tumors of the walnut-fed mice were only about half the size of the tumors in the mice that were not fed walnuts.
“What this study showed is that we had a significant suppression of cell proliferation in the walnut-fed group,” said W. Elaine Hardman, Ph.D., lead investigator and associate professor at the Marshall University’s Joan C. Edwards School of Medicine. “The time it took the tumor to double in size was 11.1 days for the corn oil fed mice compared to 23.3 days in the walnut fed group.”
That such a small dose of walnuts could exert such influence intrigued investigators. “I was surprised by the results because, compared to most dietary studies, we were adding a very small amount to the diet and I didn’t think this amount would be enough to suppresses the growth as much as it did,” Hardman added.
Walnut Components Display Anti-Cancer Potential
Although the current study is the first to investigate the effects of whole walnuts on cancer, individual walnut components have displayed the ability to slow or prevent cancer in previous investigations.
One of those components, a type of omega-3 fatty acid called alpha-linolenic acid (ALA), sets walnuts apart from other nuts, according to AICR’s Collins. “Walnuts are one of the few plant foods that contain this kind of omega-3 fat, which protects against heart disease, inflammation and – potentially – cancer as well.” Canola oil and flaxseed are also sources of ALA.
Studies suggest that omega-3 fats exert their influence by increasing the production of hormone-like, anti-inflammatory compounds. There is growing evidence that inflammation plays a role in the development of cancer.
Other much-studied cancer-protective substances within walnuts include gamma-tocopherol (a form of vitamin E), phytosterols and flavonoids. Lab studies funded by AICR and other organizations have shown that these compounds may slow cancer cell growth and fight inflammation.
“If it’s not the omega-3 acting alone to prevent cell proliferation, it may be a synergy among some or all of the compounds,” said Collins. “Each one of these substances might be present in too small an amount on its own, but when they all come at [the tumor] from different directions, they may have an effect.”
A Healthy, but Calorie-Dense, Food
Walnuts also contain fiber, which studies have shown can help with weight control. One caution, notes AICR’s Collins, is that walnuts pack a lot of calories into a relatively small portion.
“Calories still count, even in a healthy food that has plenty of nutrients,” she said. “It’s not a matter of adding extra handfuls of walnuts to your normal diet, it’s about substituting walnuts for other foods so you don’t increase your calorie consumption.” Because once you start gaining weight, Collin said, “you start to cross out a lot of the health benefits.”
The mice in the current study were eating enough walnuts to account for 18 percent of total daily calories (an amount equivalent to 370 calories in a 2,000-calorie human diet).
Dr. Hardman co-authored the study with Gabriela Ion, Ph.D., also of the Marshall University School of Medicine in West Virginia.
The study was funded by grants from the American Institute for Cancer Research with a matching grant from the California Walnut Commission. Neither group had any input on the study design or findings.
Read more: American Institute for Cancer Research
