How Broccoli Fights Cancer

Ginny Robards
Ginny Robards
10 minute read
October 19, 2022
Image of broccoli, which has been proven to fight cancer.
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Believe it or not, most of us have cancer cells floating around inside of our bodies. Including you.

When researchers performed autopsies of people who died from causes wholly unrelated to cancer, they found that 30% of women in their 40s had microscopic breast tumors, and 40% of men in that age group had precancerous cells in the prostate. And nearly 100% of the bodies had tiny traces of cancer in the thyroid gland, if the examiners looked hard enough. Meanwhile, only a tiny fraction of middle-aged men and women will actually be diagnosed with these cancers.

How is this possible? 

Well, cancer actually takes years, even decades, to develop to the point of being clinically recognizable. Precancerous cells have to accumulate a number of mutations before they are able to grow and invade surrounding tissues.

This enormous lag time is really good news for us. Because during this process, these nascent cancers are extremely vulnerable, giving us a big window of time in which to bolster our natural defense mechanisms. Smart nutrition is one way to do that.

Eating a diet rich in fruits and vegetables, in general, is linked to lower risk of cancer. However, if you zero in on specific types, you will find that some are better than others. 

And the strongest associations tend to be for cruciferous vegetables, such as broccoli. 

The Biochemistry of Broccoli

Broccoli boasts several compounds that are thought to disrupt latent tumor growth. But perhaps the most important one, and the one that I want to focus upon here, is sulforaphane

Broccoli does not technically contain sulforaphane, at least not when it is healthy. It is, however, an excellent source of a chemical called glucoraphanin, which is a precursor to sulforaphane. It also contains an enzyme called myrosinase, which is kept in a separate compartment within the cells of the broccoli plant. Normally, these two do not interact with one another.

But once these plant cells are damaged - like when the vegetable is chopped up or bitten into - the myrosinase and glucoraphanin get mixed together. Myrosinase then gets the opportunity to do its job as an enzyme (catalyze chemical reactions), and transforms the relatively inert glucoraphanin into the bioactive metabolite sulforaphane.

This process evolved as a booby-trap for would-be predators. Whenever insects nibble on broccoli, sulforaphane is manufactured, and the bugs are put off by the flavor. Makes sense.

But, in a happy coincidence, it has quite the opposite effect when we consume it.

The Magic of Sulforaphane

Where does cancer initially come from? This is a mind-bogglingly complex question, but cancer generally starts with mutations in cellular DNA, making that cell behave differently. These mutations often occur in response to certain toxins or oxidative stress.

Fortunately, we have evolved a number of built-in mechanisms to cope with this problem. One such mechanism is known as phase 2 detoxification, which is where enzymes attach molecules to toxins to neutralize them, and make them easier to safely excrete before they can cause trouble. 

This is where sulforaphane really shines. Sulforaphane boosts production of these powerful antioxidant enzymes, helping your body clear out environmental toxins.

Researchers in China recruited 291 people living north of Shanghai and had some of them drink a beverage that contained freeze-dried broccoli sprouts every day, and others had a control beverage without any broccoli. From day one, the group receiving the broccoli sprout drink showed a 61% increase in excretion of the cancer-causing chemical benzene in their urine, and this continued for the 12-week study period. The rate of excretion of acrolein, a hazardous air pollutant, also increased by 23%.

Ramping up detoxification, over time, leads to less DNA damage, and less risk of those troublesome mutations. When healthy young smokers ate steamed broccoli for 10 days, they experienced a 41% drop in oxidized DNA. Another similar study found that DNA strand breaks decreased by 22% in smokers and non-smokers after they ate broccoli for 10 days, compared to when they were assigned a control diet.

The Long-Term Payoff

Like I said earlier, cancer takes years to develop. That means that short-term clinical trials can’t really capture the benefits of nutritional components like sulforaphane.

In order to see how diet affects cancer, you need to follow people for a really long time. And indeed, we do see a major payoff for eating cruciferous vegetables like broccoli in long-term observational research.

Bladder cancer

Researchers at the Harvard School of Public Health followed almost 48,000 men for about ten years, during which time 252 cases of bladder cancer were diagnosed. When they analyzed dietary data, they found that total fruit and vegetable intake was not associated with cancer risk. But after they narrowed it down to cruciferous vegetable intake, they found that higher intake of this class of vegetables was linked to a 51% reduction in risk of developing bladder cancer during the study period. When they drilled down even further to individual vegetables, only the associations for broccoli and cabbage were statistically significant.

Pancreatic cancer

When researchers analyzed and compared data from pancreatic cancer and a control group of people who were otherwise similar but did not have pancreatic cancer, they found that subjects consuming more than 1.5 servings per week of raw cruciferous vegetables had 40% lower odds of having pancreatic cancer, compared to those consuming less than a half serving per week. Notably, the association was strongest for raw veggies, which makes sense since myrosinase is sensitive to heat. 

Breast cancer

Finally, researchers in Shanghai took urine samples from women with breast cancer, and compared them to cancer-free controls of the same age. They analyzed the urine for isothiocyanates, metabolites that come from consumption of cruciferous vegetables (sulforaphane is one). Those with the highest concentrations of isothiocyanates in their urine were only half as likely to have breast cancer, compared to those in the lowest quartile. This is particularly compelling because the researchers relied on objective markers of brassica vegetable intake, rather than the self-reported dietary habits of these subjects.

How to Maximize the Cancer-fighting Power of Broccoli

Keep it as fresh as possible

Storage time, as well as temperature, play a key role. Broccoli stored at normal refrigerator temperature was shown to lose almost half of its glucoraphanin content after just one week! So you want to try to eat it shortly after purchasing it - and ideally soon after it is harvested.

Does this apply to frozen broccoli as well? When researchers purchased both frozen and fresh broccoli and gave them to volunteers, they found that bioavailability of sulforaphane was 10-fold higher from the fresh than the frozen. Usually, frozen veggies are nutritionally equivalent to fresh, but this appears to be a rare exception to that rule.

Don’t overcook it

Myrosinase, the enzyme that activates sulforaphane, is sensitive to heat, so cooking for a long time or at high temperatures will prevent the chemical reaction that generates sulforaphane.

Does that mean that you need to eat broccoli raw in order to reap the benefits?

Maybe not. There is a cofactor in raw broccoli that interferes with production of bioactive sulforaphane, instead causing the plant to generate an inactive metabolite. And this cofactor is deactivated at a lower temperature than myrosinase. This means, in theory, that there is Goldilocks level of heat where we can maintain the activity of myrosinase but prevent that cofactor from sabotaging the process, leading to a net increase in sulforaphane. And indeed, it has been shown that steaming broccoli for 1-3 minutes leads to significantly more sulforaphane.

You definitely don’t want to boil broccoli; you will lose most of the glucoraphanin in the water (Plus boiled cruciferous veggies are pretty gross anyway).

Make sure to mix it up

Finally, remember that these health-promoting food compounds work together synergistically, meaning that it’s smart to eat a wide variety of fruits and vegetables rather than focusing on a single food or a single bioactive compound.

When lab rats were implanted with prostate cancer cells and then fed either tomato, broccoli, or a mixture of broccoli and tomato, all of the diets resulted in varying levels of tumor suppression. But the combination of tomato and broccoli together made the biggest difference, resulting in a 52% decrease in tumor weight at the end of the experiment.

So, definitely eat your broccoli, but don’t forget to add other veggies to your plate.

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