What Food Has Indoles? Exploring Healthful Plant Compounds

December 14, 2025 •

3 min read

Indoles are a family of organic phytonutrients primarily found in cruciferous vegetables like broccoli, cabbage, and kale. Research suggests that diets rich in these compounds may support various aspects of health, particularly hormone balance and cellular health.

Quick Summary

This article details the specific foods that contain indoles, explaining the formation process from glucosinolates and identifying the best dietary sources. It also covers preparation methods to retain these beneficial compounds.

Key Points

Cruciferous Vegetables are Key: Broccoli, Brussels sprouts, cabbage, and kale are the top dietary sources of indoles.
Formation Requires Chewing: Indoles are not present in vegetables until they are chopped or chewed, which releases the myrosinase enzyme.
Acids Convert I3C: The indole-3-carbinol (I3C) formed in vegetables converts into the more potent compound DIM (3,3'-diindolylmethane) in the stomach's acidic environment.
Consider Cooking Methods: Excessive heat, like boiling, can destroy the enzyme needed for indole formation, while chopping and waiting before cooking preserves it.
Benefits for Hormone Health: Indoles are studied for their potential to support hormone balance, particularly related to estrogen metabolism, and for cancer prevention.
Other Sources Exist: While less potent, some indoles can also be produced by gut bacteria breaking down tryptophan.
Prioritize Diverse Intake: A varied diet featuring different cruciferous vegetables is the best way to ensure a consistent intake of indoles and other phytonutrients.

The Primary Indole Source: Cruciferous Vegetables

Indoles are a class of phytochemicals known as glucosinolates, which are abundant in the cruciferous vegetable family (also known as Brassica plants). These plants are widely recognized for their health-promoting properties, with much of the credit going to their unique sulfur-containing compounds. When these vegetables are chopped, chewed, or cooked, the myrosinase enzyme is released, which breaks down glucosinolates into various indole derivatives, including indole-3-carbinol (I3C).

Some of the most indole-rich cruciferous vegetables include:

Broccoli: A well-known source, with higher indole-glucosinolate content in mature plants compared to sprouts.
Brussels Sprouts: These mini-cabbages contain significant levels of glucobrassicin, the precursor to I3C.
Cabbage: Found in green, red, and Savoy varieties, cabbage is a staple source of indole compounds and their benefits are found in both raw and fermented forms, such as sauerkraut.
Cauliflower: Contains substantial amounts of glucosinolates that convert to I3C when prepared.
Kale: This popular leafy green is another excellent source, especially green kale.
Collard Greens: A nutritional powerhouse with a high concentration of beneficial indoles.
Kohlrabi: This bulbous vegetable has been shown to have a high concentration of indole compared to other Brassica oleracea varieties.
Mustard Greens and Turnips: These less common options also contribute a healthy dose of indoles to your diet.

Indole-3-Carbinol (I3C) and its Active Metabolites

Within the group of indoles, indole-3-carbinol (I3C) is one of the most studied derivatives. The key to activating this compound is the presence of myrosinase, an enzyme that is released when plant cells are damaged through cutting or chewing. Once consumed, the acidic environment of the stomach further processes I3C into other bioactive compounds, most notably 3,3'-diindolylmethane (DIM). This conversion is crucial, as DIM is considered to be more potent and stable than I3C, and it is responsible for many of the observed health effects.

Beyond Cruciferous: Other Indole Sources

While cruciferous vegetables are the main dietary source, other foods can contribute smaller amounts of indoles or related compounds. These include:

Leafy Greens: Some non-cruciferous leafy greens may contain trace amounts of indoles.
Gut Microbiota: The amino acid tryptophan, found in high-protein foods like turkey and chicken, can be converted into indole by certain bacteria in the human gut.
Fermented Foods: Fermentation processes, especially with certain vegetables, can influence the production of beneficial compounds, though the indole content will vary.

Optimal Preparation to Maximize Indole Content

The method of preparing cruciferous vegetables significantly impacts the quantity of indoles available for absorption. The initial chopping or chewing is essential for the myrosinase enzyme to act on glucosinolates. However, excessive heat, such as boiling, can denature the myrosinase enzyme, reducing indole formation.

Chew thoroughly: Simply chewing your vegetables well helps begin the enzymatic process.
Chop and wait: After chopping or crushing cruciferous vegetables, let them sit for 10-15 minutes before cooking. This allows the myrosinase to start working before heat denatures it.
Steam lightly: Steaming for a short period is a good method for cooking cruciferous vegetables. It softens the vegetables without degrading the enzyme as much as boiling.
Avoid overcooking: Cook vegetables until just tender. Overcooked, mushy vegetables have lost more of their beneficial compounds.

Comparison of Preparation Methods on Indole Retention

This table illustrates how different cooking methods can influence the retention of indoles and their precursors in cruciferous vegetables.


Preparation Method	Effect on Myrosinase Enzyme	Potential Indole Conversion	Overall Impact on Indole Bioavailability
Raw (chopped/chewed)	Active and efficient	High, immediately upon chewing	Excellent
Lightly Steamed	Moderately active	Good, after initial chopping period	Good to Excellent
Stir-fried	Moderately active	Good, if not overcooked	Good
Blanched/Boiled	Largely denatured (inactivated)	Low, especially without initial chopping	Poor
Frozen (processed)	Denatured (blanched before freezing)	Low, depends on intestinal bacteria	Variable, generally lower

Conclusion

For those wondering what food has indoles, the answer lies primarily within the cruciferous family of vegetables. By incorporating a variety of these foods into your diet and being mindful of how you prepare them, you can maximize your intake of these valuable compounds. While research into the full scope of indoles' benefits is ongoing, the evidence for their positive impact on hormone metabolism and cellular health is robust. Opt for raw or lightly cooked preparation methods to get the most out of these powerful phytonutrients and support your overall well-being. A diet rich in foods like broccoli, kale, and cabbage is a simple and effective strategy to boost your indole consumption.

Frequently Asked Questions

Indoles are a class of plant-based compounds, or phytonutrients, derived from the breakdown of glucosinolates found in cruciferous vegetables. They are important because of their potential health benefits, which include supporting hormone balance and cellular health.

Yes. Indoles is the general term for the class of compounds. Indole-3-carbinol (I3C) is a specific type of indole compound produced from glucosinolates in cruciferous vegetables when they are prepared. When consumed, I3C is further metabolized into other active forms like DIM in the stomach.

To maximize your indole intake, you should chew your cruciferous vegetables thoroughly to release the myrosinase enzyme. You can also chop or crush the vegetables and let them sit for 10-15 minutes before cooking, which activates the enzymes before heat can denature them.

High-heat cooking methods like boiling can denature the myrosinase enzyme responsible for producing indoles. Lighter cooking methods such as steaming or quick stir-frying are better for preserving these beneficial compounds. Frozen vegetables often contain fewer active indoles because they are blanched (boiled briefly) before freezing.

While cruciferous vegetables are the primary source, some indoles can also be produced in the gut. Bacteria in the intestines can convert the amino acid tryptophan, found in high-protein foods, into indole, which then has a role in gut health.

Healthcare providers generally recommend obtaining indoles from whole food sources rather than supplements. The synergistic effect of indoles with other compounds in the plant is beneficial, and high-dose supplements can have mixed effects or potential risks that require further research.

Other foods like some leafy greens, dark chocolate, certain berries, and legumes are sometimes mentioned in relation to indole-like compounds, although the concentrations are typically much lower than in cruciferous vegetables.