The Ultimate Guide to Glucosinolates: The Real Reason Broccoli and Brussels Sprouts are So Good For You

Glucosinolates are sulfur-containing compounds found in cruciferous vegetables and are responsible for the pungent aroma and flavor of veggies like broccoli and Brussels sprouts.

What are glucosinolates?

Glucosinolates are naturally occurring glucose- and sulfur-containing compounds that are found in plants, especially cruciferous vegetables. Over 100 different glucosinolates are found in plants; however, all share a similar chemical structure, which consists of a β-D-thioglucose group, a sulfonated oxime group, and a side chain that is derived from the amino acids, methionine, phenylalanine, tryptophane, or branched-chain amino acids. Glucosinolates can be broken down into component phytochemicals, which are thought to be responsible for the positive health effects of glucosinolates (1).

How are glucosinolates processed in the body?

An enzyme called myrosinase catalyzes the breakdown of glucosinolates in the presence of water molecules, a process called hydrolysis. In plants, myrosinase is physically separated from glucosinolates and kept in specialized myrosin cells. When the plant is damaged during harvesting, freeze–thaw cycles, food preparation, or chewing, myrosinase is released from the myrosin cells. The myrosin then comes in contact with the glucosinolates and catalyzes the hydrolysis of glucosinolates into their components. In addition, myrosinase activity has been observed in the bacteria that inhabit the colon. This suggests that it is possible glucosinolates can be broken down in the gut during digestion of food (2).

The hydrolysis products of glucosinolates, many with biological activity, include indoles, substituted isothiocyanates, nitriles, thiocyanates, epithionitriles, and oxazolidinethiones (3). The specific products that are created vary depending on the plant species, the side-chain substitution, the cell’s pH level, and the iron concentration within the cell. In the body, one of these breakdown products, isothiocyanates, bind to glutathione with the help of a family of enzymes called glutathione-S-transferases and are further metabolized to become mercapturic acids. The molecules of another product, indole-3-carbonol, combine with each other to form biologically active products within the acidic environment of the stomach. One of these products is 3,3'-diindolylmethane (DIM) (4).

What foods are glucosinolates found in?

Glucosinolates are found in many cruciferous vegetables and pungent plants including broccoli, Brussels sprouts, cabbage, cauliflower, kale, bok choy, mustard, horseradish, collard greens, and radishes, arugula, rutabaga, turnips, watercress, wasabi. The highest concentrations of glucosinolates per gram of food are found in garden cress (3.9mg/g), mustard greens (2.8mg/g), and Brussels sprouts (2.4mg/g) (5).

Bioavailability of Glucosinolates

Chewing raw cruciferous vegetables leads to more contact between the enzyme that breaks down glucosinolates, myrosinase, and the glucosinolates themselves. When glucosinolates are broken down into their component parts, the body can use them in various ways. Another important aspect to keep in mind when trying to increase your consumption of glucosinolates is the method by which they are prepared. Cruciferous vegetables contain relatively high concentrations of glucosinolates; however, the method of cooking can often decrease the bioavailability of the isothiocyanates and other important by-products of glucosinolates. Raw vegetables are thought to confer a greater health benefit compared to cooked vegetables.

Health Benefits of Glucosinolates

The breakdown products of glucosinolates have a wide range of beneficial biological properties. Indole-3-carbinol, an indole, and sulforaphane, an isothiocyanate, are the most studied products of glucosinolates in terms of their cancer preventative effects. Many studies, which have been performed in animals and cells grown in a laboratory, have indicated that the products of glucosinolates can prevent cancer through the following mechanisms: protection from DNA damage, reducing the activity of carcinogens, reducing the effects of viruses and bacteria, reducing inflammation, inducing the death of cancer cells, inhibiting the formation of tumor blood vessels and inhibiting tumor cell migration.

Glusinolate breakdown products, especially indoles and isothiocyanates, have been found to inhibit cancer in several organs in rats and mice, including the bladder, breast, colon, liver, lung, and stomach (6,7). In addition, these compounds are thought to be able to slow the growth of cancer cells and can even lead to the increased death of cancer cells. One study showed that men who increased their intake of cruciferous vegetables from 1 serving to 3 servings per week had a 40% decrease in prostate cancer risk (8). One study in the Netherlands suggested that women who had a higher intake of cruciferous vegetables had a reduced risk of colon cancer (9).

One major product of glucosinolates, isothiocyanates, has been widely studied in regard to their cancer-protective properties. Isothiocyanates can alter the pathways in cells that are important for detoxification by increasing the activity of enzymes involved in the antioxidant and xenobiotic response element. As a result, this product has been shown to have biocidal activity against invading organisms including insects, plants, fungi, and bacteria. Further, colon cancer cells treated with the isothiocyanate, sulforaphane, were arrested in the cell cycle and thus were unable to grow and proliferate and also began the process of programmed cell death, called apoptosis.

Another common breakdown product of glucosinolates is indoles, of which indole-3-carbinol has been the most studied. Treating cancer cells that were grown in a lab with indole-3-carbinol led to the cells being trapped in G1 phase, and thus were unable to grow and proliferate. A few studies have shown that the biologically active components of cruciferous vegetables can positively affect certain biomarkers of cancer. For example, the indole, indole-3-carbinol reduced the growth of abnormal cells on the surface of the cervix (10).

Finally, a few studies have indicated that certain genetic predispositions, such as certain forms of the gene that encoded glutathione s-transferase, which is the enzyme that metabolizes and helps eliminate isothiocyanates from the body, may influence the association between consumption of cruciferous vegetables and lung and colorectal cancer(11-13).

Natural Ways to Boost Glucosinolates

You can increase your consumption of glucosinolates both through dietary changes and supplementation. Increasing your daily intake of cruciferous vegetables such as broccoli, Brussels sprouts, kale and the others listed above can significantly increase glucosinolate content. Furthermore, supplementation could prove to be beneficial. Dietary supplements containing extracts of broccoli sprouts, broccoli, and other cruciferous vegetables are available as well as supplements for the indoles, I3C and DIM. Some products are standardized to contain a minimum amount of glucosinolates and/or sulforaphane. However, the bioavailability of the compounds derived from these supplements is not known currently.

Glucosinolates are naturally occurring compounds that are found in cruciferous vegetables and are broken down into several compounds which studies have shown play important roles in maintaining health and preventing disease.

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