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What Are Indoles, and Why Are They Important for Health?

Medically reviewed by 
What Are Indoles, and Why Are They Important for Health?

Indoles are organic compounds found in various plants, particularly cruciferous vegetables like broccoli, cabbage, and kale. These compounds ​​have emerged as potent agents with numerous health benefits, including enhancing liver detoxification, helping with hormonal regulation, reducing the risk of diseases like cancer, and more. 

This article explores the biological significance of indoles, their health effects, and potential applications for these compounds in healthcare.


What Are Indoles?

Chemical Nature and Sources 

Indoles belong to a class of organic compounds that chemically share a bicyclic structure consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. This unique structure gives indoles their distinct biological activities.

Cruciferous vegetables such as broccoli, cauliflower, Brussels sprouts, and kale are rich sources of indoles. For example, indole-3-carbinol (I3C) is formed when these vegetables are cut, chewed, or cooked and is further transformed into its more active derivative 3,3′-diindolylmethane (DIM). These compounds are also available in supplement form. 

Biochemical Role

Indoles can be derived when sulfur-containing phytochemicals in cruciferous vegetables, known as glucosinolates, break down. These compounds give crucifers their characteristic taste and aroma and contribute significantly to their nutritional and health-promoting properties. 

Indoles play important roles in plant physiology, influencing various aspects of growth, development, and defense mechanisms to help plants survive in harsh environments and attract pollinators. Understanding these functions in plants provides insights into potential implications for human health when these plants are consumed.

Health Benefits of Indoles

Indoles play a crucial role in various physiological processes making them beneficial for health. Some health benefits of indoles include cancer prevention, detoxification support, anti-inflammatory activity, and hormonal support.

Cancer Prevention 

Research suggests that indoles such as I3C and DIM exert anti-cancer effects by modulating estrogen metabolism, inhibiting cell proliferation, inducing apoptosis (programmed cell death), and suppressing angiogenesis (the formation of new blood vessels that support tumor growth).

Support for Detoxification 

Indoles boost the activity of enzymes involved in detoxification pathways in the liver to support the transformation and elimination of harmful substances and certain hormones like estrogen from the body. 

Anti-Inflammatory Properties 

Indoles are powerful antioxidants that help neutralize harmful free radicals in the body that can cause damage to cells. In this way, indoles can combat oxidative stress and reduce the risk of chronic diseases, including cancer, diabetes, cardiovascular diseases, and neurodegenerative disorders. These antioxidant properties contribute to the potent anti-inflammatory effects of indoles. 

Hormonal Balance 

By promoting the conversion of estrogen to its less harmful forms, indoles help maintain hormonal balance, supporting reproductive health and helping to prevent hormone-related cancers

Cardioprotective Effects

Indoles offer cardioprotective effects, including modulation of vascular function, inflammation, and oxidative stress, that may make them valuable for preventing cardiovascular diseases such as atherosclerosis, hypertension, and coronary artery disease

Dietary Sources of Indoles

Rich Food Sources: 

Some of the richest dietary sources of indoles are plant-based foods like cruciferous vegetables, leafy greens, other vegetables, fruits, and legumes. 

Cruciferous Vegetables:

  • Broccoli
  • Cauliflower
  • Brussels Sprouts
  • Kale
  • Cabbage
  • Bok Choy
  • Turnips
  • Radishes

Leafy Greens:

  • Spinach
  • Swiss Chard
  • Collard Greens

Other Vegetables:

  • Eggplant
  • Zucchini
  • Bell Peppers
  • Mushrooms


  • Berries (e.g., blueberries, strawberries, raspberries)
  • Oranges
  • Pineapple


  • Soybeans
  • Lentils
  • Chickpeas

Preparation and Cooking Tips: 

To maximize the indole content and bioavailability of cruciferous vegetables and other indole-rich foods, eat them raw or opt for cooking methods that preserve their integrity and enhance nutrient absorption like light steaming. 

Chewing your cruciferous vegetables well and/or chopping them and letting them sit before lightly cooking can also help you maximize the bioactivity of indoles and resulting health benefits. Combining indole-rich foods with foods that are high in vitamin C such as citrus fruits, bell peppers, and strawberries can help improve the bioavailability of indoles in the body.

These foods can be easily incorporated into meals and snacks such as 

  • steaming some broccoli and bell peppers
  • blending greens and berries into a smoothie
  • making a comforting lentil and veggies stew
  • roasting a mix of vegetables as a side dish

Supplementation and Safety

Indole Supplements: 

Indole supplements containing I3C or its derivative DIM concentrated doses of indole compounds derived from cruciferous vegetables or synthetic sources. They are commonly used for hormone balance, detoxification, and prevention of cancers of the breast, prostate, and cervix.

While supplements offer more concentrated doses of indoles, their absorption and utilization by the body may differ from those obtained through dietary sources. Since indole supplements can have powerful impacts on hormones and detoxification and may therefore interact with certain medications, it is important to consult with a healthcare provider before starting any new supplement regimen.

Safety Considerations: 

Indoles are generally considered safe for consumption when obtained from dietary sources such as cruciferous vegetables. A balanced diet incorporating 2-3 servings of cruciferous vegetables per day can provide an adequate intake of indoles for most individuals. 

However, it is important to remain mindful of potential side effects, especially impacts on thyroid function and medication interactions. It is also important to individualize supplement protocols to balance each individual’s physiology. For example, DIM supplements may need to be used in conjunction with other supplements like calcium D-glucarate or broccoli sprouts/sulforaphane to keep hormones in balance. 

While human studies are limited, there is some concern that very high intakes of cruciferous vegetables and/or indole supplements may contribute to insufficient production of thyroid hormones as indoles can compete with iodine uptake by the thyroid gland, especially in those with insufficient iodine levels.

Due to their impacts on detoxification enzymes in the liver, indole supplements may impact the levels of certain medications including hormone replacement therapy and oral contraceptives.

Current Research and Future Directions

Emerging research has highlighted additional health benefits of indoles beyond their well-known impacts on hormone balance, detoxification, and cancer prevention

Gut Health

Recent studies suggest that indoles can be generated within the body (endogenously) via metabolism by gut microbes. They appear to exert positive effects on gut health by modulating the gut microbiota, improving the intestinal barrier, and enhancing immune function


Indoles also show promise in promoting neuroprotection, potentially helping to prevent neurodegenerative conditions like Alzheimer's and Parkinson's. These compounds are important mediators in the gut-brain axis and help reduce neuroinflammation

Metabolic Improvements

There is growing interest in indoles’ impacts on metabolic health and the prevention of obesity, diabetes, and metabolic syndrome. Indoles improve metabolic parameters such as lipid metabolism, insulin sensitivity, and energy balance. 

Immune Health

Indoles have immunomodulatory effects, influencing the activity of immune cells and promoting a balanced inflammatory response.

Heart Health

Recent studies show that indoles favorably modulate fibrosis, a key process in the development of cardiovascular disease.

Potential Future Therapeutic Applications

Based on this emerging research, indoles hold promise for future therapeutic applications across various health conditions. The beneficial anti-inflammatory, metabolic, and immunomodulatory effects of indoles make them valuable in many therapeutic areas.

Ongoing research into indoles' influence on gut-brain axis communication offers the potential for improving gastrointestinal health and neurological function and addressing autoimmunity. 


Key Takeaways

  • Indoles have antioxidant, anti-inflammatory, detoxification-promoting, and anticancer effects.
  • Including indole-rich foods in the diet, such as cruciferous vegetables, leafy greens, fruits, and legumes, optimizes intake of this potent compound.
  • Supplements containing indole compounds like indole-3-carbinol (I3C) and diindolylmethane (DIM) offer more concentrated doses and should be used with the guidance of a healthcare provider to ensure safe and effective use.
  • Emerging research shows numerous medicinal uses and health benefits of indoles for the immune system, gastrointestinal tract, nervous system, metabolism, and cardiovascular system due to their antioxidant, anti-inflammatory, detoxification, and hormonal balancing effects. 
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.
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