“For years, the United States government has been on a crusade against fat, and I think it’s been to our detriment,” says lead scientist and research nutritionist Paul Davis. “Walnuts are a perfect example. While they are high in fat, their fat does not drive prostate cancer growth. In fact, walnuts do just the opposite when fed to mice.”
Davis and colleagues have been investigating the impact of walnuts on health for some time. A previous study showed that walnuts reduced prostate tumor size in mice; however, there were questions about which parts of the nuts generated these benefits. Was it the meat, the oil, or the omega-3 fatty acids?
If it was the omega-3 fats, the benefit might not be unique to walnuts. Since the fatty acid profile for the soybean oil used as a control was similar, but not identical, to walnuts, more work had to be done.
Not Omega-3s Alone
The results replicated those from the previous study. While the walnuts and walnut oil reduced cholesterol and slowed prostate cancer growth, in contrast, the walnut-like fat did not have these effects, confirming that other nut components caused the improvements—not the omega-3s.
“We showed that it’s not the omega-3s by themselves, though, it could be a combination of the omega-3s with whatever else is in the walnut oil,” Davis says. “It’s becoming increasingly clear in nutrition that it’s never going to be just one thing; it’s always a combination.”
While the study does not pinpoint which combination of compounds in walnuts slows cancer growth, it did rule out fiber, zinc, magnesium, and selenium.
In addition, the research demonstrated that walnuts modulate several mechanisms associated with cancer growth, including the hormone IGF-1.
“The energy effects from decreasing IGF-1 seem to muck up the works so the cancer can’t grow as fast as it normally would,” Davis says. “Also, reducing cholesterol means cancer cells may not get enough of it to allow these cells to grow quickly.”
In addition, the research showed increases in both adiponectin and the tumor suppressor PSP94, as well as reduced levels of COX-2, all markers for reduced prostate cancer risk.
Eat More Walnuts?
Although results in mice don’t always translate to humans, Davis says his results suggest the benefits of incorporating walnuts into a healthy diet. Other research, such as the PREDIMED human study, which assessed the Mediterranean diet, also found that eating walnuts reduced cancer mortality.
Still, Davis recommends caution in diet modification.
“In our study the mice were eating the equivalent of 2.6 ounces of walnuts,” he says. “You need to realize that 2.6 ounces of walnuts is about 482 calories. That’s not insignificant, but it’s better than eating a serving of supersized fries, which has 610 calories.
“In addition to the cancer benefit, we think you also get cardiovascular benefits that other walnut research has demonstrated.
The study was published online in the Journal of Medicinal Food.
Other researchers included Hyunsook Kim of Konkuk University and Wallace Yokoyama of the Western Regional Research Center.
The American Institute for Cancer Research, the California Walnut Board, and Konkuk University funded the study.
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*Image of “walnuts” via Shutterstock