Cancer is, without hesitation, the most universally feared disease. While treatments have come a long way, there is still a life-long concern or possible death sentence that comes with a cancer diagnosis.
According to the Centers for Disease Control and Prevention (CDC), the most common include prostate cancer in men/breast cancer in women, lung cancer and colorectal cancer.
Of these, colorectal cancer in particular has been shown to be highly responsive to dietary choices. In fact, some studies indicate that up to 50 percent of colorectal cancer in men and about 20 percent of the cancer in women could be prevented with proper dietary and lifestyle changes.
In addition to increasing fiber intake, research has shown that eating nuts and seeds can help reduce the incidence of colorectal cancer. Flaxseed in particular has been shown to be especially beneficial.
On the nut front, walnuts have been found to inhibit the growth of breast cancer cells in mice. And walnut extract has even been shown to slow the growth of colon cancer cells in the lab. But how do walnuts work against colorectal cancer in a living organism? According to Boston researchers, quite well.
Nuts Versus Seeds Versus Cancer
Researchers set out to determine the effect walnuts would have against colorectal cancer in mice. But, they didn’t stop there. They also wanted to see how well the nuts worked against a known cancer fighter like flaxseed.
To answer this question, researchers used 48 six-week old female mice and injected them with human colon cancer cells. Seven days later, researchers divided the mice into three groups:
1. Walnut group (received the equivalent of two servings of walnuts per day for humans, or about 376 calories in human terms)
2. Flaxseed oil group (similar calorie composition as walnut group)
3. Control (received corn oil with similar calorie composition as the other groups)
The mice were fed their respective diets for 25 days (for a total experiment length of 32 days). All mice were weighed and had their tumors measured three times a week.
At the end of the 32 days, the mice were sacrificed and researchers measured several cancer markers.
They found that body weight increased similarly across all three groups and slowed as the days went on.
When it came to fatty acid composition, the corn oil group had very little omega-3s (such as alpha linolenic acid, or ALA) and higher amounts of the omega-6 EFA linoleic acid (LA), with a ratio of 43:1 LA to ALA. The flaxseed group had very little LA and high amounts of ALA, with a ratio of 1:5 LA to ALA. The walnut group had similar levels of LA to the corn oil group, but also had higher levels of ALA, with a ratio of 6:1 LA to ALA. (We’ll discuss why this is important in a minute.)
When it came to tumor size, the tumors grew significantly in the first seven days, then slowed significantly in both the walnut (27 percent) and flaxseed (43 percent) groups as compared to the control group. In fact, the final tumor weight of the walnut group was reduced by 33 percent, while the flaxseed group had a 44 percent reduction, as compared to the control group.
Interestingly, both the walnut and flaxseed groups showed large, central areas of dead tissue within the tumors. The control group did not have these large areas, and, in fact, had much more viable tumor tissue. More specifically, the total area of dead tissue in the walnut and flaxseed groups was nearly twice that of the control group.
When it came to angiogenesis (the growth of new blood vessels, which is an indication of cancer growth), the control group had increased activity, as indicated by greater tumor vessel density, as compared to the walnut and flaxseed group.
But here’s where the walnut and flaxseed groups finally show some differentiation. When it came to the vascular endothelial growth factor (VEGF), which stimulates new blood vessel formation, the flaxseed group had 20 percent less than the control group, while the walnut group had a whopping 70 percent less VEGF.
Walnut’s Secret Powers
Researchers hypothesized that the secret to walnut’s cancer-fighting powers lies in its ability to down-regulate VEGF, thereby inhibiting angiogenesis in tumors. This cuts off the blood supply to the tumor, which causes it to not only stop growing, but to start dying off.
When all factors were taken into account, the researchers found that walnuts slowed colorectal cancer growth by 30 percent, while flaxseed inhibited growth by 45 percent. But when it came to suppressing angiogenesis, walnuts were nearly three times more effective than flaxseed.
Researchers went on to suggest that one of the reasons both flaxseed and walnuts appear to be so effective in fighting colorectal cancer is due to their ALA concentration. ALA is the precursor of the better-known omega-3 fatty acids EPA and DHA. Both of these omega-3s have been shown to slow tumor growth and metastases in the lab as well as in animals.
Additionally, human studies have shown that ALA supplementation with either flaxseed oil or walnuts helps to increase blood levels of both EPA and DHA. Finally, ALA itself has been shown to reduce inflammation and improve insulin resistance, both of which have been associated with increased risk of colorectal cancer progression.
Based on this background and the findings of the present study, researchers concluded, “Isocaloric amounts of walnuts and flaxseed oil, compared with corn oil, inhibit colorectal cancer growth.”
Get Nutty and Seedy
With cancer rates on the rise and our diets getting worse and worse, it’s nice to know that such simple (and delicious!) solutions are out there.
To reap the cancer-protective benefits of walnuts, you’ll want to aim for two servings of raw, unsalted walnuts a day (about a half cup total). Fortunately, there are many easy ways to get this “dosage”:
- Sprinkle them on a salad
- Crush them and use them to coat chicken or fish before lightly sautéing
- Stir them into yogurt
- Grind them into a butter and enjoy with celery or crackers
- Simply eat as is!
To enjoy the benefits of flaxseed oil, aim for 2 to 4 tablespoons per day. Again, there are many ways to get your flax oil:
- Replace olive oil with flax oil on a salad
- Add it to a smoothie
- Double your health benefit and add to a walnut butter puree
- Stir into oatmeal
- Simply pour onto a spoon and drink
 United States Cancer Statistics. 1999–2007 Cancer Incidence and Mortality Data. http://apps.nccd.cdc.gov/uscs/.
 Parkin, MD et al. The potential for prevention of colorectal cancer in the UK. Eur J Cancer Prev. 2009;18:179-90.
 Nagel, JM et al. Dietary walnuts inhibit colorectal cancer growth in mice by suppressing angiogenesis. Nutrition. 2011 Jul 26. [Epub ahead of print.]