How Much Does Diet Contribute to Cancer Risk?

How Much Does Diet Contribute to Cancer Risk?

(Last Updated On: April 11, 2019)

image of cancer fighting foods

Cancer is the disease no one wants. Although heart disease is more common, cancer is a disease that hits us at an emotional level. Fortunately, treatments are constantly advancing and we know more about what causes cancer and potential ways to slow its progression than ever before.

The current theory is that cancer arises from mutations to DNA, a cell’s blueprint for producing proteins. These mutations allow cells to grow out of control and to invade normal tissue. They often also acquire the ability to evade the immune system, the system that could keep them in check, and to metastasize or move to other tissues. Cancer really isn’t one disease but a group of diseases and malignant tumors can arise from different cell types.

Unfortunately, one in two men and one in three women will develop cancer over the course of a lifetime. It might seem that cancer is a disease over which we have no control, but we now know that lifestyle plays a role. For example, studies clearly link smoking with lung cancer. Another area of focus is on diet. It would be reassuring if we could make simple dietary changes to lower the risk of cancer. But, first, how much does diet contribute to the risk of developing cancer?

Diet and Cancer

What we eat impacts almost every aspect of our functioning and also is a factor in whether or not we develop cancer. Studies show that 30 to 35% of cancers are related to diet while another 25 to 30% can be blamed on smoking. This means that our food choices DO have an impact and diet is something we have control over. We can choose broccoli over a doughnut, right? Makes you feel a little more empowered!

If you look at epidemiological studies, you can see that cancer incidence changes with major dietary switches. For example, back in the 1950s, the Japanese ate a diet heavy in plant-based foods. However, their diet had changed by the 1990s to include more animal-based foods. Along with this change, the incidence of colon cancer cases increased by 5-fold. A number of studies reveal a correlation between colon cancer and the consumption of meat. For example, the Nurses’ Health Study showed a link between greater consumption of pork, beef, and lamb and a higher incidence of colon cancer.

Diet impacts the risk of other forms of cancer as well. For example, studies have identified a connection between higher consumption of fruits and vegetables and a lower risk of some cancers. One way that these foods may be protective is they contain chemicals that decrease oxidative damage of DNA. Certain components of foods, such as EGCG in green tea allicin in garlic also, in the laboratory, slow the growth of cancer cells.

Another component of fruits and vegetables that offer protective benefits is fiber, a dietary component most people get too little of. In fact, the average American only gets about half the recommended amount of fiber each day. How might fiber lower cancer risk? Fiber is poorly digested. As such it passes through the digestive tract unchanged where it helps to carry carcinogens and bile breakdown products out of the body. The breakdown products of bile are linked with colon cancer. A higher fiber diet also helps lower the body’s estrogen burden, a factor that may reduce the risk of breast cancer. Although some studies show that a higher fiber diet protects against colorectal cancer, others do not.

So, it’s not clear whether eating more fiber really does lower colon cancer risk. Still, most people need more of it!

Eating more fiber has another benefit as well – It helps with satiety. That’s important since weight gain and obesity are linked with thirteen different types of cancer. Simply losing weight lowers the risk of these cancers and that starts with eating a healthy, whole food, unprocessed diet that’s also high in fiber.

A Healthy Immune System Protects Against Cancer

We count on our immune system to identify and wipe out cancerous cells that form inside your body all the time. Fortunately, a healthy immune system can identify these rogue cells and destroy them. Anything that suppresses immunity, including drugs and certain viruses, increase cancer risk. That’s where getting enough micronutrients by eating a nutrient-rich diet comes into play.

Deficiencies of certain micronutrients, particularly folate, contributes to DNA damage that can trigger the growth of cancer. However, taking micronutrients in supplement form is not linked with a reduced risk of cancer. Whole foods are best! Carotenoids in dark, leafy greens and orange fruits and vegetables, like carrots, are associated with a diminished risk of some types of cancer. Again, supplements don’t appear to lower the risk and there’s some evidence of harm.

Vitamin D is vital for immune health and studies have looked at whether people who consume more vitamin D are at lower risk of cancer. Here, too, studies are inconsistent – some show benefits while others do not. Still, we know that vitamin D helps regulate the immune response and a healthy immune system helps fight cancer.

Another reason to eat an unprocessed diet. Some studies also link rapidly absorbed carbohydrates with a greater risk of cancer. It makes sense since quickly absorbed carbs cause a more pronounced insulin response and insulin acts as a growth factor for cells, including tumor cells. One study showed a higher risk of lung cancer in men who ate a diet rich in processed carbs.

Limit Alcohol

Another dietary component associated with a higher risk of a certain cancer is alcohol. The strongest association is with cancer of the head, neck, esophagus, and liver and most pronounced in people who drink 3 or more alcoholic beverages daily. However, a study showed a small rise in breast cancer risk in women who drank slightly less than one drink daily.

The Bottom Line

Yes, diet does contribute to cancer risk and it’s a factor you can control. So, make sure you’re eating a healthy, whole food diet and doing other things, like staying physically active to lower your risk. Also, know your family history, so you’re aware of what cancers you’re at greatest risk for.



Harvard Health Publications. “Cancer and diet: What’s the connection?”
Molecular Biology of Cancer: Mechanisms, Targets, and Therapeutics. Third edition. Lauren Pecorino.
Oncol Rev. 2015 Feb 10; 9(1): 288.
Biofactors. 2000;13(1-4):89-94.
National Cancer Institute. “Vitamin D and Cancer Prevention”
Harvard Health Publications. “Cancer and diet: What’s the connection?”
National Cancer Institute. “Alcohol and Cancer Risk”


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