Prostate cancer is the second most common cancer among men in the United States (second only to skin cancer), killing just under 28,000 US citizens in 2011, according to the US Centers of Disease Control and Prevention (CDC).

Past research has indicated that omega-3 fatty acids may actually be effective at reducing a man's chances of developing the cancer - bolstering arguments from a new nutrition movement that says our condemnation of all things fatty is actually harming public health.

However, while the jury may still be out on the benefits and consequences of a fatty diet, a new study has determined that omega-3 alone is not the cancer preventer that experts hoped it was. Instead, the walnut may actually be the 'prostate protector,' but the reason for this remains unclear.

Why walnuts? Past omega-3 studies often used walnut oil as the sample source, as walnuts boast high concentrations of the fatty acid. Strangely, according to a study recently published in The Journal of Medicinal Food, compared to other omega-3 sources, walnut oil is far more effective at lowering prostate cancer risk and slowing tumor growth.

This was determined after researchers fed mice either walnuts, walnut oil, or a mixture of fats with the same omega-3 fatty acid content as walnuts. And while the walnuts and walnut oil performed exactly as they premised, slowing prostate tumor growth in the lab rodents, the omega-3 mixture had no such effect.

However, lead scientist and research nutritionist Paul Davis is quick to point out that this doesn't rule out omega-3 fatty acids entirely.

"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," he said in a statement. "It's becoming increasingly clear in nutrition that it's never going to be just one thing; it's always a combination."

Davis and his team also noted that you don't have to eat a ton of walnuts to receive their health benefits.

"In our study the mice were eating the equivalent of 2.6 ounces of walnuts (about 482 calories)," he explained. "That's not insignificant, but it's better than eating a serving of supersized fries, which has 610 calories."

"It's the holiday season, and walnuts are part of any number of holiday dishes," Davis added. "Feel free to consume them in moderation."

Your prostate may thank you for it.