Public health officials and nutrition experts love to sing the praises of the virtuous cruciferous vegetable family. We are told that these pungent plants can fight off cancer, strengthen our immune system, and leap tall buildings in a single bound. But could crucifers have a dark side?
The cruciferous veggies (the Brassica family) dominate the produce aisle; many people may not realize how many familiar vegetables belong to this family.
List of Cruciferous Vegetables
- Bok choy
- Brussels sprouts
- Chinese Broccoli
- Chinese cabbage
- Choy sum
- Collard greens
- Mustard Greens
- Mustard Seeds
These mustard family members are notorious for giving off a strong odor that sends children ducking for cover underneath the dinner table. That lovely aroma is due to the presence of sulfur-containing chemicals called “thiocyanates.” These are natural plant defense compounds, designed to protect the plant from potential invaders.
Plants are cunning. If they need us to help them disperse their seeds, they will package the seeds in a colorful, appealing fruit and fill it with the sweet sugars we love to eat. However, they do not want us to eat their stalks, roots, stems, and leaves—the vital body parts that keep the plant alive, so they tend to make those parts bitter. Plants do not want to be eaten any more than animals do, but since they can’t run, growl, bite, or claw at creatures that want to feast upon them, they have evolved, over hundreds of millions of years, some very sophistical chemical weapons to ward off hungry passers-by.
Let’s use broccoli as our signature crucifer, as it is the best-studied. Like all cruciferous veggies, broccoli uses isothiocyanates to protect itself. The one it happens to use is called sulforaphane, which is made this way:
Glucosinolate + Myrosinase (enzyme) = SULFORAPHANE
When broccoli is sitting peacefully in a field (cue the flute solo), it does not contain any sulforaphane. This pungent molecule is so toxic to living cells (including broccoli’s own cells) that the two harmless ingredients needed to make it are stored in separate compartments within broccoli cells. However, if the cells’ defenses are breached—if the vegetable is cut or bruised or if an insect or small animal comes along and bites into its flesh (cue the ominous organ music)—the individual compartments break open, the two ingredients mix together, and POOF! Sulforaphane—a chemical weapon with the power to kill things like insects, bacteria, and worms.
How does sulforaphane kill tiny living creatures, and why should you care?
You should care because sulforaphane can do the very same things to your cells that it does to the cells of the little guys:
- Poisons mitochondria (cell energy generators)
- Inhibits microsomal enzymes in the endoplasmic reticulum (cellular manufacturing and detoxifying centers)
- Generates reactive oxygen species (these are damaging “pro-oxidants”)
- Interferes with thyroid iodine absorption
- Disrupts epithelial barriers (can poke holes in sheets of cells)
- Depletes glutathione levels (the most important antioxidant inside our cells)
All of the above mechanisms explain how sulforaphane can kill small living creatures. In research studies it has also been demonstrated that sulforaphane can kill healthy human cells and can cause cancerous changes in human cells.
It may come as a surprise to you to learn that this sulforaphane is the very same broccoli ingredient that we are told is responsible for the health benefits of broccoli. The reason for these health claims lies in the other things that sulforaphane does in research studies:
- Induces cancer cell apoptosis (causes cancer cells to commit suicide)
- Inhibits angiogenesis (slows new blood vessel formation, which is how cancers grow)
- Induces “phase II enzymes” (fires up human immune system antioxidants)
- Kills bacteria (natural antibiotic)
So, as you can see, sulforaphane is a double-edged sword, capable of killing bacteria and cancer cells, as well as killing healthy cells and even causing cancer. Just like any form of chemotherapy, this compound does not do a very good job of distinguishing between cancerous cells and healthy cells, so collateral damage (friendly fire) may occur.
Why do we only hear about broccoli’s superhero side, and not its villainous dark side? As a psychiatrist and someone who has read far too many nutrition articles, I can confidently say this: when it comes to food and health, believing is seeing. If we believe something is good for us, we only see evidence to support that belief and are almost incapable of seeing evidence to the contrary. The belief that vegetables are good for us comes entirely from epidemiological studies, which are only capable of generating untested theories about food and health. Scientific experiments are then conducted to try to support those beliefs, and the truth is that these experiments yield very mixed results about how broccoli affects us.
Scientists who are aware of the dark side of crucifers defend them as superfoods by invoking the concept of hormesis. The hormesis theory essentially says that small amounts of toxic compounds can actually be good for you—this is the “what does not kill you makes you stronger” argument. However, when it comes to crucifers and health, this is just a hypothesis. What’s more, even if it were true, then the best advice about crucifers would be to eat them in small amounts to ensure tiny doses of isothiocyanates. Instead, the prevailing wisdom about crucifers is: the more, the merrier.
- Sprouts contain 20 to 100 times more glucosinolate than mature vegetables (to protect the baby plant).
- Freezing crucifers or boiling them for 10 minutes reduces glucosinolate concentrations by about 50%.
- Steaming reduces glucosinolate concentrations by about 2/3.
- Heat completely destroys myrosinase. However, the bacteria in our gastrointestinal tract contain enzymes that mimic myrosinase, so sulforaphane will still be generated in the process of digestion.
- About 75% of all sulforaphane in the digestive tract is absorbed into the bloodstream and taken up by cells throughout the body. Blood levels peak about 2 hours after eating crucifers.
- Once inside cells, our own natural cellular antioxidant, glutathione, rapidly binds to sulforaphane and escorts it out of cells to be eliminated within 3 hours.
Some scientists have postulated that our cells get rid of sulforaphane as quickly as possible precisely because it is an unwanted guest–an irritant, rather than a helpful tool in our cancer-fighting arsenal.
So, is broccoli good for you?
We really don’t know. I was unable to find any convincing clinical evidence to support the health benefits of crucifers, but I did find enough interesting scientific evidence to at least call their health benefits into question. Most humans and their ancestors have been eating vegetables for tens if not hundreds of thousands of years. Therefore, even if broccoli may be potentially harmful to us, we have likely evolved ways to minimize any damage it may cause. Case in point: although we do absorb significant amounts of sulforaphane, our cells rapidly evict it. However, individuals with chemical sensitivities, weakened immune systems, liver disease, and /or gastrointestinal problems may be more likely to experience symptoms related to the natural chemicals in certain vegetables, which are usually not suspected as potential culprits. People with hypothyroidism (under-active thyroid) may also want to consider removing cruciferous vegetables due to their potential to interfere with normal thyroid activity.
Are children who hate broccoli onto something? Out of the mouths of babes…
For information about how cruciferous vegetables can aggravate IBS in some people, click HERE to read my blog post about constipation.
To watch a 20-minute video of my vegetable presentation entitled Little Shop of Horrors, the Risks and Benefits of Eating Vegetables, given at the 2012 Ancestral Health Symposium, click HERE.
To read more about vegetables in general, click HERE to be taken to my vegetables page.
Assayed M and Abd El-Aty AM. Cruciferous plants: phytochemical toxicity versus cancer chemoprotection. Mini-rev Medic Chem 2009: 1470-1478.
Cavell BE et al. Anti-angiogenic effects of dietary isothiocyanates: Mechanisms of action and implications for human health. Biochemical Pharmacology 81 (2011) 327–336.
Hayes DP. Nutritional hormesis. European Journal of Clinical Nutrition 2007; 61, 147–159.
Herr A et al. Dietary constituents of broccoli and other cruciferous vegetables: implications for prevention and therapy of cancer. Cancer Treatment Reviews 2010; 36: 377–383.
Latte KP et al. Health benefits and possible risks of broccoli–an overview. Food and Chemical Toxicology 2011;49: 3287-3309.
Nakamura Y and Miyoshi N. Electrophiles in foods: the current status of isothiocyanates and their chemical biology. Biosci Biotechnol Biochem 2010; 74(2): 242-255.
Rungapamestry V et al. Effect of cooking brassica vegetables on the subsequent hydrolysis and metabolic fate of glucosinolates. Proceedings of the Nutrition Society 2007; 66: 69–81.
Yanaka A et al. Dietary sulforaphane-rich broccoli sprouts reduce colonization and attenuate gastritis in Helicobacter pylori-infected mice and humans. Cancer Prev Res 2009; 2:353-360.
Zhang Y and Callaway EC. High cellular accumulation of sulphoraphane, a dietary anticarcinogen, isfollowed by rapid transporter-mediated export as a glutathione conjugate. Biochem J 2002; 364(Pt 1): 301-7.