How Glucosinolates and Isothiocyanates Promote Health

In this interview, Jed Fahey, Sc.D., a nutritional biochemist, assistant professor at Johns Hopkins Medical School,1 and director of the Cullman Chemoprotection Center,2 reveals why cruciferous vegetables are such nutritional gems.

Fahey has spent the past four decades of his life researching plant compounds and the medicinal benefits of vegetables. His extensive training includes plant physiology, human nutrition, phytochemistry and nutritional biochemistry.

In the early '90s, he began working with Paul Talalay, a renowned pharmacologist and cancer prevention scientist at Johns Hopkins. Talalay died in March 2019 at the age of 95.3

"Prevention was a fairly radical theory back then, 25 years ago," Fahey says, "but I was delighted to join forces with professor Talalay. Over the last 25 years, that's pretty much what we've done.

We've tried to, as we'd like to say, put teeth in the recommendations that you should eat more plants … We've tried to understand and bring to the public ideas about how and why the phytochemicals in plants … can enhance one's health span and allow one to live a longer life in full vigor."

Toxic to Insects but Beneficial for You

One plant chemical with well-established health benefits is sulforaphane, found primarily in the cruciferous vegetable broccoli. Sulforaphane is produced from a glucosinolate called glucoraphanin, which is found in greatest abundance in broccoli sprouts and seeds.

Glucoraphanin, which is essentially inert in and of itself, is converted into a bioactive isothiocyanate called sulforaphane, through an enzyme called myrosinase.

"Isothiocyanates are biologically active and act as feeding deterrents," Fahey explains. "They act as toxins to insects. Many of them are bactericidal to varying degrees."

As such, they act (within the plant) as natural pest repellants. Evolutionarily, that's what they were designed to do. When consumed, those compounds trigger protective enzymes in your cells, thereby ratcheting up your endogenous defense mechanisms, one of which is the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway.

"That's the primary one that was discovered by folks here at Johns Hopkins … the Nrf2 pathway [is] highly responsive to isothiocyanates and upregulates a whole host of antioxidant and other protective enzymes," Fahey says.

Interestingly, sulforaphane and moringin (from the plant Moringa oleifera) and other isothiocyanates also tamp down the proinflammatory nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) response in humans.

They may actually have an effect on the heat-shock response, which has to do with protein folding and rescue of proteins from damage. There is a rather daunting list of beneficial biological activities that these isothiocyanates have. But the Nrf2 pathway is certainly the key pathway that we started looking at and that is certainly a primary defensive mechanism that's upregulated."

Why Nrf2 Pathway Is so Important for Health

As explained by Fahey, the Nrf2 pathway is vitally important for human health. Nrf2 is a nuclear transcription factor found in the cytoplasm of the cell, where it's tethered by a chaperone protein called Keap1.

When molecules like sulforaphane cross the membrane and enter the cell, it binds to Keap1, which then releases Nrf2 from its molecular tether, allowing it to migrate to the nucleus where it binds with an antioxidant response element.

That in turn allows the transcription of a whole suite of antioxidant and chemoprotective genes, which trigger the formation of proteins, many of which are chemoprotective enzymes.

"In our scientific ratings, we frequently talk about compounds like sulforaphane being an indirect antioxidant. It's an important concept, because when you upregulate these antioxidant enzymes, you allow for protection against oxidative stress in those cells in which these enzymes are upregulated," Fahey explains.

"These enzymes are rather long-lasting. In other words, they hang around in the cell and the tissue for a matter of certainly hours, in most cases, days …

We refer, for example, to sulforaphane and isothiocyanates as indirect and as long-lasting antioxidants because they crank up the activities of these antioxidant enzymes. In and of themselves, though, these molecules, like sulforaphane, are not direct antioxidants like, for example, vitamin C.

Many of the other antioxidants that folks are probably familiar with … protect against reactive oxygen species, reactive nitrogen species, and then they're gone. They have to be replaced or replenished."

Benefits of Indirect Antioxidants Such as Sulforaphane

Importantly, direct antioxidants indiscriminately suppress free radicals — including beneficial free radicals — which is likely why many studies looking at antioxidant supplementation have concluded it doesn't appear to increase longevity or health span.

Sulforaphane and other indirect antioxidants, on the other hand, stimulate the activation of the antioxidant response elements only when it's needed. What's more, the activation of Nrf2 is generally believed to be hormetically controlled, meaning that while a small amount is beneficial, a large amount may have the opposite effect.

"We don't know enough about the dose yet," Fahey admits. "We've been working on that … But we can approximate a dose based on what people who eat a lot of broccoli [or Moringa], for example, would eat …

Based on our knowledge of the chemistry, we can measure the amount of glucosinolates in these plants … But yes, one can have too much and one can have too little."

Fahey believes dosing with sulforaphane may be done as infrequently as every third day, because it basically increases the production and activity of enzymes that stay in the body for a period of time before going away.

Upregulation of Heat-Shock Proteins Is a Major Benefit

Sulforaphane also upregulates heat-shock proteins, which play a crucial role in protein folding, allowing misfolded proteins to be properly refolded. Most people are completely unaware of the need for refolding proteins.

Remarkably, about one-third of the proteins your body makes are misfolded, which means they don't work properly. Many of these then go on to form nonfunctional aggregates. Heat-shock proteins refold them back to a functional shape, and if they are too misfolded to be repaired, they mark them for destruction and recycling. This is one of the major benefits that isothiocyanates provide. Fahey further explains:

"The heat-shock pathway or the heat-shock response is extremely important and these protein chaperones are certainly biologically very important …

I'm not the expert on heat-shock … The interesting story I want to tell, though, is that, yes, the sulforaphane, the moringin from Moringa and other isothiocyanates do appear to upregulate the heat-shock response.

About 10 years ago, Dr. Andrew Zimmerman, who at the time was at Harvard and Mass General, came to Talalay … [Zimmerman] is an expert in autism.

He said, 'Interestingly, some kids who have autism and get a fever, their symptoms resolve. They get much better. When the fever goes away, their symptoms come back … Your group and others have shown that sulforaphane upregulates the heat-shock response. Wouldn't it be cool if these two things were connected and if sulforaphane might have an effect on autism?'"

Sulforaphane May Benefit Children With Autism

While this sounded farfetched, Talalay's team, which included Fahey, conducted a small clinical study4 with Zimmerman in 2007, which was published in 2014. Forty-four autistic boys and young men (aged 13 through 27) were given a daily dose of oral sulforaphane for 18 weeks.

"Quite remarkably … there was a dramatic and significant, substantial reduction in symptoms of autism [in] … more than half of the children," Fahey says. However, once they stopped taking the sulforaphane, the symptoms returned to baseline.

A follow-up study, which checked back on the participants three years later, found almost all of the caregivers had put their children on a commercial sulforaphane supplement, and many reported a lessening of symptoms in that time. In all, there are now five follow-up studies on the use of sulforaphane for autism.

"It all stems from the idea that maybe this is a heat-shock response that is involved," Fahey explains. "We are looking for biochemical molecular markers of the heat-shock response in at least some of the follow-up studies."

On Supplement Timing

Sulforaphane also facilitates detoxification by upregulating liver and cytochrome enzymes that aid in the removal of toxic molecules. Normal human metabolism can be roughly divided into two phases:

  1. Autophagy — the breakdown phase
  2. Catabolism — the rebuilding phase

Activating detox enzymes is best done during autophagy, which occurs during periods of fasting. And, while no studies have specifically looked at the timing of sulforaphane supplementation, Fahey agrees with this general theory.

What this means is that you may reap the greatest benefits if you take it after your last meal for the day, and then avoid eating for 16 hours thereafter. That said, Fahey argues there might be benefits to taking it first thing in the morning on an empty stomach as well:

"I think one could make the argument that if one gives it in the morning on an empty stomach as one is starting to go about one's daily business and being exposed, for example, to air pollution …

One might argue that if the work that sulforaphane does in the body — the upregulation or protective enzymes — happens rapidly (and it does), that maybe it's better to give it first thing in the morning to protect against the insults of the day."

The counter-argument could be that toxic exposures are generally stored in fat cells, and are eliminated during the detox phase. From yet another perspective, if the upregulation of enzymes does continue for up to three days (which it appears to do), then timing may actually be somewhat irrelevant.

The good news is research conducted at Johns Hopkins shows that daily dosing for three months does not fatigue the Nrf2 pathway response, meaning your body does not appear to develop a resistance to it. In other words, continuous and prolonged dosing does not inhibit or "wear out" your detoxification system.5

Glutathione Upregulation Is Likely a Key Benefit

Speaking of detoxification; as mentioned, isothiocyanates are plant toxins — chemicals that are toxic to pests, bacteria, fungi and so on — yet they end up being beneficial when ingested by humans. While Fahey did not have a clear-cut answer as to why that is, he offers the following theory:

"We do know — from work that my colleague, Yuesheng Zhang, did 20 years ago — that when your body's cells sees sulforaphane, they take it up. It's rapidly taken up. It's concentrated in the cell to a couple of hundred times concentration [seen] in the blood and the interstitial tissue.

It's rapidly conjugated with glutathione and then it's dumped back out of the cell, unceremoniously and quickly. In the process, in the cell, the Nrf2 pathway and all these other pathways are upregulated. But it is viewed as a toxin. It is detoxified.

And perhaps it's that detoxification mechanism, that cranking up of glutathione, which is the body's most prevalent antioxidant, that's doing the good things. That's the direct antioxidant, which it's upregulating. And then those molecules have a chance to stay around long after sulforaphane is gone."

Many clinicians recommend supplemental glutathione to boost detoxification, which I believe is a mistake. Not only is it poorly absorbed and expensive, but it's also far better to have your body make it than to take it exogenously. Using sulforaphane to upregulate glutathione appears to be a far better alternative, and you don't need a supplement to do that — just eat isothiocyanate-rich foods, such as:

  • Moringa, which contains a powerful isothiocyanate called 4-(α-L-rhamnopyranosyloxy)-benzyl glucosinolate, better known as moringin, that is just as potent as sulforaphane, and in some assays actually more potent
  • Broccoli and broccoli sprouts, which contain sulforaphane
  • Arugula, which contains the chemoprotective isothiocyanate erucin,6 is also the richest plant source of dietary nitrates that are converted into beneficial nitric oxide
  • Mustard seed, which in addition to allyl isothiocyanate7 also contains high amounts of myrosinase enzyme, required for the conversion of glucoraphanins into bioactive isothiocyanates. One way to significantly boost the bioavailability of sulforaphane in broccoli, for example, is to eat it with a bit of mustard seed, daikon, kale, wasabi or horseradish, all of which contain myrosinase

Cooking Guidelines

As noted by Fahey, "We're killing ourselves with processed food." Indeed, Fahey's work demonstrates just how important real food is — you won't find any of the plant components discussed here in your average processed meal. And, without them, you're missing out on many valuable self-healing mechanisms.

Proper preparation and cooking is important, though. When you eat the plant, myrosinase in the plant is released, which is needed for the conversion of inactive glucoraphanins into bioactive isothiocyanates. Certain gut bacteria also aid in the conversion by producing myrosinase.

"There's some production of isothiocyanates in a time-dependent and person-dependent manner," Fahey says. "When we study bioavailability, it's all over the map. It's hard to predict who's going to do what. Your gut is full of microbes … and those microbes have myrosinase activity. They will do the conversion."

To optimize the health benefits from broccoli, it's important to cook it just right. Eating raw cruciferous vegetables or moringa gives you active myrosinase. The degree to which you cook the food will, to some extent, inactivate the myrosinase. "Moderate or very light cooking or steaming is fine, but I wouldn't argue that it spares all the myrosinase necessarily," Fahey says.

Supplements and Teas

If you don't like cruciferous vegetables, then taking a glucoraphanin supplement is a reasonable thing to do, Fahey says. He believes that even if you're not getting myrosinase with it (although there are supplements that also include myrosinase, which would be preferable), your intestinal bacteria should still be able to achieve the needed conversion, although you may end up needing higher dosages if your conversion is low.

"It is hard to tell how much conversion there will be, unless you do a urine test and a chemical test," he warns. If you buy a supplement with myrosinase in it, it would probably be wise to refrigerate it, as myrosinase is an enzyme that can degrade over time.

Another drawback with supplements is the quality. "There are some supplements on the market now — some of them good, some of them useless," Fahey says. Another alternative is Moringa leaf tea, the health effects of which Fahey has investigated and written a paper on.8

"I have two to three cups of Moringa leaf tea every day as I'm working. I'd rather drink that than coffee, if I don't feel like I have to have caffeine. There are various ways to deliver it. Those who read scientific papers, keep your eyes peeled for a paper on Moringa tea."

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