Colorectal Cancers

Colorectal cancer (includes colon and rectal cancer) is a growth of malignant cells that starts in the large intestines and may grow and spread to other parts of the body.

  • Overview
  • Action Plan
  • Ask The Doctor
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Colorectal cancer is a common cause of death in the U.S., and approximately 1 in 20 (5%) will be diagnosed with colorectal cancer in their lifetime.1 You may not know you have colorectal cancer until it has progressed, which is why screening has been suggested over the years as a useful strategy to lower death risk from this disease. If there are any of the following signs or symptoms, you may want to talk to your doctor:

  • Anemia
  • Severe constipation or obstruction
  • Abdominal pain
  • Blood in your stool
  • Fatigue
  • Unexplained weight loss

All cancers have causes that are multifactorial, but they are not inevitable and not the normal consequence of aging. One’s diet is the major factor increasing one’s risk or decreasing one’s risk of colon cancer. A systematic analysis by scientists of the World Cancer Research Fund reviewing over 1000 studies on bowel cancer risk has confirmed that red meat increases risk and high fiber plant foods decrease the risk. This strengthens WCRF/AICR’s* recommendation for people to consume a plant-based diet including whole grains, fruits, vegetables, and beans.

A small percentage of people who develop colorectal cancers had a genetic or inflammatory condition that was related to their elevated risk, however, scientific findings indicate that there are many factors that can lower the risk of developing colorectal cancer. Alcohol use, tobacco use, being overweight, being sedentary, eating meats (especially processed meats), and eating a low fiber diet have all been associated with a higher risk of colorectal cancer. Dietary factors can be significant when added all together. Cooking meats and processed meats at high temperatures, such as with grilling, broiling, or frying, increases risk, and when combined with very low fiber intake from vegetables, fruits, legumes, and whole grains, this can be synergistic at raising risk. Protective nutrients from these same high fiber plant foods may be actively working against cancer from developing, and an emphasis on the foods with the most protective nutrients is the best strategy.

  1. Siegel R, Desantis C, Jemal A. Colorectal cancer statistics, 2014. CA Cancer J Clin 2014, 64:104-117.

*World Cancer Research Fund/American Institute for Cancer Research’s (WCRF/AICR) Continuous Update Project (CUP)

Action Plan


  • Many plant foods have been found to contain cancer-fighting nutrients, which can be eaten regularly for prevention or as part of a treatment regimen for colorectal cancer. Of the foods studied, the following has shown the most convincing evidence for protection.
    • Seeds—Seeds are high in fiber and have anti-inflammatory properties, which lower risk.
    • Green vegetables, particularly cruciferous vegetables (such as broccoli, kale, cabbage, and collards)—Cruciferous vegetables contain high amounts of special sulfur-containing compounds that fight cancer and have been shown to reduce the risk of colorectal cancer.1
    • Garlic and onions—Similar to cruciferous vegetables, garlic and onions have special sulphur-containing compounds that help fight cancer.
    • Legumes (beans, lentils)—Eating beans and lentils, which are high in fiber and other protective nutrients, has been shown to be protective against colorectal cancer.2 Fiber is especially protective in the colon, in part because gut bacteria break down fiber (and resistant starch) into short-chain fatty acids which have anti-cancer effects.3, 4
    • Mushrooms—Mushrooms are helpful at reducing cancer risk, likely related to their beta-glucan content, which has anti-cancer effects.  They also contain inhibitors of cancer growth. 
    • Berries—Eating berries (strawberries, blackberries, cranberries, blueberries, etc.) have been shown to help fight cancer, likely related to their high fiber and flavonoid content.
  • Tip: Onion family and cruciferous family vegetables are best eaten raw and chewed very well, or at least chopped finely or blended prior to cooking, in order to provide the strongest cancer protection.
  • Reducing foods that are associated with higher risk, such as processed foods and animal products, is also an important strategy in reducing colon cancer risk. Red and processed meats in particular promote colorectal cancers, in part due to dietary carcinogens, such as heterocyclic amines and N-nitroso compounds.3
  • Meal plan: Anti-cancer/High micronutrient, reduced in animal products and processed foods.


  • Dr. Fuhrman’s general supplement protocol for adults (see Vitamin Advisor for details) includes:

  • Additional supplements:
    • Green tea has anti-cancer effects in vitro, drinking green tea regularly is associated with a lower risk of cancer, and studies suggest that green tea supplements may help to reduce cancer-related biomarkers.5
    • Turmeric/curcumin: Curcuminoids, the widely studied bioactive components of turmeric, have anti-cancer effects in vitro, and human studies suggest beneficial antioxidant and anti-inflammatory effects.6, 7
    • Grape seed extract has anti-cancer effect in vitro, such as inhibiting inflammation, proliferation, angiogenesis, and aromatase activity.8 Clinical trials are being conducted to find out whether grape seed extract is helpful for people with cancer or at high risk of cancer. 
    • Ultra Cell Biotect provides absorption-enhanced curcumin and green tea extract plus turmeric, grape seed extract, and black turmeric extract to help neutralize free radicals and promote cellular health. Consult your physician if you are on medication.
    • Mushroom extracts: Studies suggest that concentrated mushroom extracts may be a useful addition to cancer treatment, to decrease the immunosuppressive effects of chemotherapy.9
    • Immune Biotect provides assorted immune-supporting mushroom phytochemicals that are not normally consumed in the diet, plus astragalus, elderberry and other berry extracts. Consult your physician if you are on medication. 
    • Read more: Do you have a supplement formulated to enhance protection against cancer?


Regular physical activity is associated with lower risk of colorectal cancer.


Eat for Life

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Position Paper: IGF-1, Dietary Protein and Cancer


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Other Considerations

  • Screening is recommended. Screening methods such as colonoscopy, stool occult blood testing, and/or other methods are options for screening for colorectal cancers. Method and frequency should be discussed with your doctor and may depend on your medical history, family history, age, dietary pattern and prior screening test results.
  • Weight loss: Obesity increases the risk of several cancers, including cancers of the colon and rectum.11 Obesity is also associated with poorer prognosis in colorectal cancers.12 If you are overweight or obese, a Nutritarian diet style will help you reach your ideal weight.

Find additional help

ONLINE: All members of can search the Ask the Doctor archives for discussions on this topic. Platinum and Diamond members can connect with Dr. Fuhrman by posting questions in the forum. Not a member? Join now.

IN PERSON: Book a stay at Dr. Fuhrman’s Eat to Live Retreat in San Diego, California. With options ranging from one, two and three months (and sometimes longer) you will be under Dr. Fuhrman’s direct medical supervision as you hit the “reset” button on your health. For more information: (949) 432-6295 or [email protected]

EVENTS: Join Dr. Fuhrman for an online boot camp, detox or other event. During these immersive online events, you’ll attend zoom lectures, follow a special meal plan, and have access to a special, live Q&A session with Dr. Fuhrman. Learn more about events.

  1. Tse G, Eslick GD. Cruciferous vegetables and risk of colorectal neoplasms: a systematic review and meta-analysis. Nutr Cancer 2014, 66:128-139.
  2. Wang Y, Wang Z, Fu L, et al. Legume consumption and colorectal adenoma risk: a meta-analysis of observational studies. PLoS One 2013, 8:e67335.
  3. World Cancer Research Fund/American Institute for Cancer Research: Continuous Update Project. Colorectal Cancer 2011 Report. Food, Nutrition, Physical Activity, and the Prevention of Colorectal Cancer. 2011 []
  4. Aune D, Chan DS, Lau R, et al. Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies. BMJ 2011, 343:d6617.
  5. Khan N, Mukhtar H. Cancer and metastasis: prevention and treatment by green tea. Cancer Metastasis Rev 2010, 29:435-445.
  6. Park W, Amin AR, Chen ZG, Shin DM. New perspectives of curcumin in cancer prevention. Cancer Prev Res (Phila) 2013, 6:387-400.
  7. Panahi Y, Hosseini MS, Khalili N, et al. Antioxidant and anti-inflammatory effects of curcuminoid-piperine combination in subjects with metabolic syndrome: A randomized controlled trial and an updated meta-analysis. Clin Nutr 2015, 34:1101-1108.
  8. Katiyar SK, Athar M. Grape seeds: ripe for cancer chemoprevention. Cancer Prev Res (Phila) 2013, 6:617-621.
  9. Patel S, Goyal A. Recent developments in mushrooms as anti-cancer therapeutics: a review. 3 Biotech 2012, 2:1-15.
  10. Kolb R, Sutterwala FS, Zhang W. Obesity and cancer: inflammation bridges the two. Curr Opin Pharmacol 2016, 29:77-89.
  11. Aleksandrova K, Nimptsch K, Pischon T. Obesity and colorectal cancer. Front Biosci (Elite Ed) 2013, 5:61-77.
  12. Doleman B, Mills KT, Lim S, et al. Body mass index and colorectal cancer prognosis: a systematic review and meta-analysis. Tech Coloproctol 2016, 20:517-535.

Ask The Doctor

The following are sample questions from the Ask the Doctor Community Platinum and higher members can post their health questions directly to Dr. Fuhrman. (All members can browse questions and answers.)


Do you have a supplement formulated to specifically to enhance protection against cancer?


Dietary supplements by definition do not treat, prevent, or cure a disease and cannot claim to on labels or in advertising. However, plant extracts are continually being studied for their potential to maintain health and affect the disease process.  Clinical trials are being conducted, aiming to figure out whether certain plant extracts could affect cancer-related biomarkers, act as beneficial adjunct treatments to be used with chemotherapy, or help to prevent progression of an early stage cancer or pre-cancerous condition. Read more


I had my first colonoscopy at age 50, which was fine. Now, 10 years later, the office has called telling me to schedule another one. Since the first one, I have lived a Nutritarian lifestyle (with few exceptions) and have no family history that I’m aware of. Is it necessary to repeat a colonoscopy every 10 years while maintaining a Nutritarian lifestyle?


While I can’t give you specific recommendations, we know that people who are at optimal weight, who are not insulin resistant, who eat a nutrient, fiber rich diet with limited animal protein, and who are active and exercise have reduced risk of colon cancer. Though I strongly believe a Nutritarian diet offers dramatic protection from cancer, the diet in your childhood and the earlier part of your adult life plays a role in this risk. So, since you only started the Nutritarian diet 10 years ago and had only one negative colonoscopy, I would have just one more and then never again after that if staying with dietary excellence, however, this is just an educated guess. Again, I have no specific recommendations based on scientific studies, so I cannot give definitive guidelines here; it still is personal decision after a discussion with your primary physician. If there is a family history, every 5 years may be recommended.


I have colon cancer and am curious how many ounces of animal products a week you recommend and which kind?


In the context of this post, the answer would be no animal products. Animal products promote anabolic hormones (especially IGF-1) that can induce cell proliferation increasing the risk or growth of the cancer. A vegan Nutritarian diet (with green juices) is more appropriate for a person with cancer.


Aside from mushrooms and cruciferous vegetables within a Nutritarian diet, are there specific foods you’d recommend for colon cancer patients? How about supplements in addition to Women’s Daily Formula, DHA/EPA Purity, Immunotect, and Osteo-Sun?


Read my book, Super Immunity, or the newsletter that gives the protocol for those with cancer. You may be aware, I recommend a large raw salad every day, and that salad includes raw cruciferous vegetables such as cabbage, watercress, kale or collards as well as raw onion and tomato with a nut/seed based dressing to facilitate absorption. And for those with cancer or at higher risk of cancer, in addition to this large raw salad, I also recommend a blended salad at an additional meal or a glass of green-based juice. Don’t forget the other G-BOMBS, and that means beans, berries, and ground flax and chia seeds. Eliminate or severely limit animal products and sugar. It’s the entirety of the diet that is beneficial. Exercise is also important. Studies have shown that exercising 4-5 hours/week reduces the risk of colon cancer recurrence and mortality significantly. There are no additional supplements I would recommend, though some early evidence suggests digestive enzymes have some benefits for those who have cancer.


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