According to a new study published in the Journal of Medicinal Food, scientists at the University of California-Davis have found that a diet rich in walnuts, or its oil, can slow prostate tumor growth. Prostate cancer is one of the most common cancers among men. Prior studies have already shown that walnuts may protect against certain cancers and heart disease due to their high levels of omega-3 fatty acids. However, this new research suggests the omega-3s are not working alone – making the benefit unique to walnuts.
Scientist and research nutritionist, Paul Davis, and a team of researchers had been studying the heart benefits of walnuts for some time. In a prior study, they even found that walnuts reduced prostate tumor size in mice. However, it was unclear which part of the nut was responsible. They decided to take a closer look at the three possibilities: the oil, the omega-3 fatty acids, or the meat.
In the study, mice were fed oil from walnuts, whole walnuts, or a walnut-like control diet including omega-3 fatty acids for 18 weeks. The mice were genetically programmed to develop prostate cancer. The results showed that the walnuts and the walnut oil reduced the levels of IGF-1 – a hormone known to be implicated in both prostate and breast cancer. While the groups on the walnut and walnut oil diet exhibited a reduction in prostate tumor growth, the omega-3 group did not.
Eighteen weeks into the study, the group on the walnut diet displayed a tumor mass 30 to 40 percent smaller than the mice on the control omega-3 fat diet. Six weeks later, the group on the walnut diet was still showing a reduction in tumor mass, relative to the group on the walnut oil diet. In addition, both the walnut group and the walnut oil group showed a reduction in cholesterol and an increase in insulin sensitivity. The omega-3 group did not. This suggests that the walnut oil and other parts of the walnut are responsible for the benefit – not the omega-3s.
In regards to which part of the walnut is responsible, Davis suggests it is a combination of things. However, it is still unclear exactly what that combination is. They were able to rule out zinc, magnesium, selenium and fiber. “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 said. “It’s becoming increasingly clear in nutrition that it’s never going to be just one thing; it’s always a combination.”
Walnuts are special in that they are able to fight inflammation. Inflammation is linked to heart disease as being an underlying cause. Inflammation is also known to be associated with the development of many cancers including prostate cancer. Inflammation is the body’s response to tissue being damaged as a result of injury, infection, or exposure to toxins. The inflammatory response causes the damaged cells to repair themselves and promotes cell growth at the injured site. If inflammation persists, it can become chronic and in turn create an environment that is favorable for the development of cancer.
The researchers say that the amount of walnuts needed – if future studies on humans exhibit similar results – would not require much. Even just a handful (one-quarter cup) of walnuts a day provides more than the entire recommended daily amount of omega-3 fats. Walnuts are a powerful antioxidant and are most nutritious when consumed as a whole, including the skin. Up to 90 percent of the antioxidants in walnuts are found in the skin. In addition to potentially protecting against prostate cancer and other cancers, walnuts are also beneficial for heart health, brain health, diabetes, weight control, and improved reproductive health in men.