Subscribe to the Magazine for free
Subscribe for free to keep reading! If you are already subscribed, enter your email address to log back in.
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
Are you a healthcare practitioner?
Thanks for subscribing!
Oops! Something went wrong while submitting the form.

Indoles for Cancer Prevention: Understanding the Protective Role of Cruciferous Vegetables

Medically reviewed by 
 Indoles for Cancer Prevention: Understanding the Protective Role of Cruciferous Vegetables

Indoles, bioactive compounds found predominantly in cruciferous vegetables, are noted for their potential role in cancer prevention. It’s vital to understand how indoles contribute to lower cancer risks, as scientific evidence supports indole efficacy regarding numerous health conditions

This article demonstrates ways to incorporate indole-rich foods or supplements into daily meal plans as an effective cancer-preventive health strategy.


What Are Indoles?

Indoles are phytochemicals present in cruciferous vegetables, including broccoli, cauliflower, and cabbage. Their chemical makeup consists of heterocyclic aromatic compounds with fused pyrrole and benzene bicyclic rings. Indoles come from the breakdown of glucosinolates (sulfur-containing phytochemicals) found in certain vegetables.

The metabolism of indoles in the human body transforms these substances into compounds with significant biological activity, offering various health benefits. Examples include reduced inflammation, hypertension (high blood pressure), diabetes, cancer, and more. 

While the potential advantages of indoles are endless, these anti-cancer compounds aren’t for everyone in high amounts.

The Link Between Indoles and Cancer Prevention

Research supports the benefits of consuming indoles for cancer prevention. 

These phytochemicals contribute to cancer reduction by reducing carcinogens, protecting DNA from damage, repairing mutated genes, reducing cancer cell growth, and speeding up cancer cell death.

Indoles also help maintain hormone balance, reducing the risk of certain types of cancer. Studies show that indoles appear to influence estrogen metabolism, lessening the chance of hormone-dependent cancers (endometrial cancer, breast cancer, ovarian cancer, etc.). 

The researchers also found a link between cruciferous vegetable consumption and lower rates of kidney, prostate, colorectal, endometrial, and digestive tract cancers

Studies demonstrate that indole-3-carbinol (I3C), a type of indole, helps suppress tumor growth and that indole-rich foods boost the conversion of estrogen from cancer-producing forms to less harmful products.

Additional research shows that I3C in cruciferous vegetables stimulates natural detoxifying enzymes, boosts carcinogen (and other toxin) elimination, and enhances liver health. 

The anti-inflammatory properties of indoles have profound potential impacts on chronic disease prevention, as studies suggest these phytochemicals optimize intestinal health and lessen the risk of inflammatory bowel disease (IBD) and colorectal cancer

Dietary Sources of Indoles

The following cruciferous vegetables are exceptional sources of indoles:

  • Broccoli: broccoli contains about 62 milligrams of glucosinolates in a 100-gram serving. Glucosinolates break down into indoles and other biologically active compounds.
  • Brussels sprouts: Brussels sprouts are loaded with indoles, containing an astounding 237 milligrams of glucosinolates in each 100-gram portion of raw sprouts. 
  • Cabbage: cabbage provides 59 grams of indole-producing glucosinolates in each 100-gram serving.
  • Cauliflower: cauliflower offers 43 grams of glucosinolates per 100-gram raw serving size.
  • Collard greens: collard greens provide a whopping 201 grams of glucosinolates in each 100-gram portion.
  • Kale: Kale consists of 89 grams of glucosinolates in each 100 grams.
  • Kohlrabi: kohlrabi contains 46 grams of glucosinolates per serving (100 grams).
  • Radishes: 100 grams of raw radishes contain 93 grams of glucosinolates.
  • Turnips: turnips also provide 93 grams of glucosinolates in each 100-gram portion.

Choose a variety of these and other vegetables at each meal to increase the consumption of fiber, vitamins, minerals, antioxidants, indoles, and other phytochemicals.

Maximizing the Cancer-Preventive Effects of Indoles

To optimize your intake of indoles and reap numerous health benefits, aim for the following goals:

  • Consume at least 2 ½ cups (or 5 cups of leafy green) vegetables daily when following a 2,000-calorie meal plan. Choose a variety of cruciferous and other vegetables to meet this daily goal. 
  • To preserve the glucosinolate and indole content of cruciferous vegetables, eat them raw or steam them. Studies show that other cooking methods (stir-frying, boiling, and microwaving) decrease the amount of phytochemicals in these veggies. 
  • Eat an abundant amount of plant-based foods (fruits, vegetables, nuts, seeds, whole grains, avocados, plant oils, etc.) to minimize the risk of cancer and other chronic diseases. 
  • Eat cruciferous vegetables dipped in hummus, plain Greek yogurt, guacamole, or other nutritious dips. 
  • Add indole-rich foods to salads, soups, stews, smoothies, green juices, slaws, wraps, sandwiches, dips, casseroles, or any other favorite recipe to increase its nutritional content and cancer-fighting effects.
  • Consult with a healthcare professional for personalized diet planning advice and supplement use recommendations.
  • Combine cruciferous vegetables with other natural anticancer nutrients (folic acid, vitamin B12, vitamin D, selenium, carotenoids, lycopene, etc.) abundant in fruits and vegetables.

Studies show that these cancer-fighting nutrients help reduce colorectal, breast, prostate, and lung cancers. The researchers found that meats and other animal-based foods high in fat and generally cooked at high temperatures could increase the risk of stomach, prostate, and colorectal cancers. 

Supplementation: Pros and Cons

Indole supplements, including indole-3-carbinol (I3C) and diindolylmethane (DIM), are alternative sources of highly concentrated indoles. Over-the-counter doses typically range from 100-800 milligrams daily for I3C or DIM supplements, though there are no established safety guidelines — especially for pregnant and nursing women.

Indole supplements provide potential pros and cons, including:


Ingesting indole supplements is a simple way to consume large amounts of health-promoting phytochemicals. These supplements may reduce the risk of cancers and other chronic diseases.


When choosing indole supplements instead of indole-rich foods, you won’t be getting all of the fiber, vitamins, minerals, antioxidants, or other cancer-fighting micronutrients abundant in cruciferous vegetables.

In high amounts, indole-rich vegetables or supplements could cause bloating, gas, interactions with blood-thinning medications, or health concerns for people with thyroid disease

Potential side effects of higher-dose indole supplementation may include tremors, disequilibrium, gastrointestinal symptoms, and skin rashes. These supplements could reduce the effectiveness of certain medications

Considerations and Potential Limitations

While indoles are highly effective phytochemicals that may prevent cancer, check with your doctor before eating large amounts of cruciferous vegetables or taking indole supplements. This is particularly true if you have a thyroid condition or take any medications. 

Phytochemicals alone may not eliminate the chance of developing cancer, as lifestyle and genetic factors both contribute to overall cancer risks. For example, if someone in your family has cancer or you adopt unhealthy lifestyle habits, your risk of cancer increases. 


Key Takeaways

The potential health benefits of indoles are endless, as they’re a key factor in cancer-preventive diets. Indoles:

  • Are abundant in cruciferous vegetables (broccoli, cauliflower, cabbage, etc.) and indole supplements
  • Have anti-cancer properties by reducing carcinogens, protecting DNA from damage, speeding up cancer cell death, repairing mutated genes, and slowing cancer cell growth
  • Help reduce toxin buildup, inflammation, hypertension, and chronic disease risk factors 
  • Aid in hormone balance to lessen the risk of hormone-linked cancers
  • May reduce the risk of breast, ovarian, kidney, prostate, colorectal, endometrial, and digestive tract cancers
  • A holistic approach to cancer prevention includes consuming a well-balanced diet rich in fruits, vegetables, and other plant-based foods; exercising regularly; healthy weight management; and not smoking or drinking alcohol in excess. 
  • Always check with a doctor to determine if you’re a candidate for indoles or other dietary supplements, and which dosage is safest.
  • Incorporate indole-rich cruciferous vegetables into weekly meal plans as part of a comprehensive strategy for health promotion and cancer risk reduction. 
The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
Learn More
No items found.

Lab Tests in This Article

No items found.

Auborn, K. J., Fan, S., Rosen, E. M., Goodwin, L., Chandraskaren, A., Williams, D. E., Chen, D., & Carter, T. H. (2003). Indole-3-Carbinol is a negative regulator of estrogen. The Journal of Nutrition, 133(7), 2470S2475S.

Blake, K. (2023a, April 28). What is a heart healthy diet and who should follow one? Rupa Health.

Blake, K. (2023b, December 15). The power of functional foods in cancer prevention. Rupa Health.

Chadha, N., & Silakari, O. (2014, April 29). Indole-3-Carbinol. Linus Pauling Institute.

Christie, J. (2022, December 13). 95% of Americans aren’t getting enough fiber: How many grams should we be consuming per day?

Christie, J. (2023, January 6). A functional medicine approach to obesity and weight management. Rupa Health.

Cleveland Clinic. (2013). Estrogen and cancer: Information & risks | Cleveland Clinic. Cleveland Clinic.

Cloyd, J. (2023a, April 28). What is the difference between medical-grade supplements and over-the-counter supplements? Rupa Health.

Cloyd, J. (2023b, May 18). Complementary and integrative medicine approaches to managing high blood pressure: Specialty testing, lifestyle modifications, and natural remedies. Rupa Health.

Cloyd, J. (2023c, October 27). Macro and micronutrients uncovered: Understanding their role, deficiencies, and clinical relevance. Rupa Health.

DeClercq, V., Nearing, J. T., & Sweeney, E. (2022). Plant-Based diets and cancer risk: What is the evidence? Current Nutrition Reports, 2.

DePorto, T. (2023, January 10). Timeline: What happens inside your body when you quit smoking? Rupa Health.

Diorio, B. (2023, April 7). Could your patients benefit from the phytonutrient spectrum food plan? Rupa Health.

Ellis, E. (2020, August 13). The beginners guide to cruciferous vegetables.

Food guides for prostate health. (2024). University of California San Francisco .

Indole-3-Carbinol. (2010). Memorial Sloan Kettering Cancer Center.

Kalaichandran, A. (2024, February 13). The link between dietary antioxidants and alzheimer’s disease. Rupa Health.

Katz, E., Nisani, S., & Chamovitz, D. A. (2018). Indole-3-carbinol: A plant hormone combatting cancer. F1000Research, 7, 689.

Licznerska, B., & Baer-Dubowska, W. (2016). Indole-3-Carbinol and its role in chronic diseases. Advances in Experimental Medicine and Biology, 131–154.

Malani, S. (2023a, April 17). An integrative medicine approach to breast cancer prevention. Rupa Health.

Malani, S. (2023b, May 11). Complementary and integrative therapies for treatment and recovery of ovarian cancer. Rupa Health.

Mentella, M. C., Scaldaferri, F., Ricci, C., Gasbarrini, A., & Miggiano, G. A. D. (2019). Cancer and mediterranean diet: A review. Nutrients, 11(9), 2059.

Montgomery Hays, B., & Hudson, T. (2020). Indole-3-Carbinol - an overview | sciencedirect topics.

National Cancer Institute. (2015, December 23). Risk factors. National Cancer Institute;

Sweetnich, J. (2023a, March 22). Selenium 101: Testing, top foods, and supplements. Rupa Health.

Sweetnich, J. (2023b, March 24). Vitamin A 101: Health benefits, testing, & top foods. Rupa Health.

Sweetnich, J. (2023c, April 26). Unlocking the benefits of vitamin B12: The importance of maintaining optimal levels. Rupa Health.

Sweetnich, J. (2023d, May 4). Getting to know vitamin D: From testing to supplementing and meeting your rda’s. Rupa Health.

Sweetnich, J. (2023e, May 8). Understanding the importance of folate testing and proper supplementation for optimal health. Rupa Health.

This is why mom said to eat your broccoli (and other cruciferous veggies). (2023, June 6). Cleveland Clinic.

Thomson, C. A., Ho, E., & Strom, M. B. (2016). Chemopreventive properties of 3,3′-diindolylmethane in breast cancer: Evidence from experimental and human studies. Nutrition Reviews, 74(7), 432–443.

UCLA Health. (2023, May 10). What are phytochemicals? (And why should you eat more of them?).

USDA. (2020). Dietary guidelines for americans 2020 -2025. In Dietary Guidelines for Americans. USDA.

Weinberg MD, J. L. (2023, January 24). Functional medicine treatment for graves’ disease. Rupa Health.

Weinberg, J. L. (2024a, January 2). Impact of plant-based diets on chronic inflammation reduction. Rupa Health.

Weinberg, J. L. (2024b, February 2). A functional medicine approach to colon polyps. Rupa Health.

Weng, J.-R., Tsai, C.-H., Kulp, S. K., & Chen, C.-S. (2008). Indole-3-carbinol as a chemopreventive and anti-cancer agent. Cancer Letters, 262(2), 153–163.

Ye, X., Li, H., Anjum, K., Zhong, X., Miao, S., Zheng, G., Liu, W., & Li, L. (2022). Dual role of indoles derived from intestinal microbiota on human health. Frontiers in Immunology, 13.

Yoshimura, H. (2023a, April 26). Complementary and integrative medicine approaches to oncology in gerontology. Rupa Health.

Yoshimura, H. (2023b, October 10). A root cause medicine approach to chronic inflammation. Rupa Health.

Yoshimura, H. (2023c, November 7). The remarkable power of exercise on our health: A comprehensive overview. Rupa Health.

Yuan, G., Sun, B., Yuan, J., & Wang, Q. (2009). Effects of different cooking methods on health-promoting compounds of broccoli. Journal of Zhejiang University SCIENCE B, 10(8), 580–588.

Subscribe to the Magazine for free to keep reading!
Subscribe for free to keep reading, If you are already subscribed, enter your email address to log back in.
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
Are you a healthcare practitioner?
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
See All Magazine Articles