Broccoli vs Cancer — A New Analysis
This Week’s Research Highlight
Background
Vegetable consumption has long been shown to be protective against cancer. This association is connected to chemical properties found in edible plants. Plants have evolved thousands of chemical compounds to shield themselves against oxidative stress and DNA damage. When we eat plant foods that contain these chemicals, we benefit, to a degree, from these protective effects as well.
Now, eating more vegetables in general appears to show this impact, when researchers collect dietary data and follow people for long enough to see cancers emerge. However, when researchers zero in on specific types, they usually find that some are better than others. And the strongest link seems to be for cruciferous vegetables.
One major standout is broccoli. Broccoli is notable because it is a rich source of a compound that can ramp up production of enzymes that help cells resist toxins — including carcinogens.
A number of observational studies have been conducted to figure out whether and to what extent broccoli can influence cancer development. Yet findings in this area have been conflicting (more on that later).
To try to clear things up, researchers in Spain recently performed the most comprehensive review and meta-analysis to date on this subject.
Study Design
Spanish researchers searched databases to identify all published epidemiological studies that examined the association between broccoli consumption and cancer. These studies fell into two main subcategories of observational research, each of which look at the link between diet and cancer from a different angle.
First, they examined 23 case–control studies (12,929 cases and 18,363 controls; total of 31,292 individuals). A case-control study is where researchers compare the dietary habits of patients with cancer to otherwise similar individuals who did not have cancer. This is a common research design for studying rare diseases, like many cancers, but it does come with some significant limitations. Most notably, these studies are retrospective, meaning that they rely on participants to recall what their diets looked like years ago, before the start of the study. So, in such a study, researchers might be asking cancer patients and healthy controls to report how much broccoli they habitually ate six years ago, or something like that.
Then, the researchers analyzed 12 cohort studies (total = 699,482 individuals). Cohort studies are prospective — they follow people over time and determine how various factors that were measured at the start of the study are associated with incidence of a disease later on. So, for example, a researcher might recruit 50,000 individuals who do not have cancer at baseline, ask them about their diets, and then follow them for 15 years and see whether the people who ate more broccoli were more or less likely to wind up being diagnosed with cancer.
The meta-analysis, in total, included 35 observational studies with data from more than 730,000 participants.
Results
The analysis of the case-control studies found that high intake of broccoli (meaning anywhere from once a week to daily) was linked to 36% lower odds of cancer. When the researchers narrowed their focus to specific types of cancer, they found that broccoli consumption was linked to lower odds of bladder cancer, reproductive cancers, pancreatic cancer, gastric cancer, and cancers of the lung or respiratory tract.
Meanwhile, the analysis of the cohort studies showed that higher broccoli consumption was associated with 11% reduced risk of going on to develop cancer.
(High consumption, in this context, would mean anywhere from weekly to daily intake of broccoli, while low consumption would range from a few times a month to never)
Underlying Mechanisms
Broccoli has a lot going for it nutritionally, with multiple compounds that may have anti-carcinogenic properties. However, there is one in particular that seems especially potent. Broccoli contains a chemical called glucoraphanin, which is stored in compartments inside their tissues next to an enzyme known as myrosinase. When the plant is injured (like when it is bitten into, or cut with a knife), these compartments are ruptured, and myrosinase is mixed together with glucoraphanin. Then, as they are combined, myrosinase converts glucoraphanin into sulforaphane, an active form that serves as a defense for the plant.
Sulforaphane has emerged as one of the more powerful cancer-fighting compounds found in common foods, increasing production of enzymes that detoxify cancer-causing chemicals that you eat or encounter in the environment. Human experiments have shown that having people consume broccoli sprouts increases excretion of carcinogenic pollutants, which in turn means less DNA damage and less risk of dangerous mutations.
Taking a closer look at some of the epidemiological studies in this area also lends support to this mechanism. Notably, one observational study found that individuals with higher concentrations of these types of metabolites in their urine were half as likely to have cancer, which certainly suggests that these bioactive compounds might be responsible for the observed association. Furthermore, some of these studies have found that raw cruciferous vegetables are much more strongly linked to reduced cancer risk than cooked. This is pertinent here because exposure to high temperatures has been shown to degrade myrosinase, the enzyme that converts glucoraphanin into sulforaphane. Without that enzyme activity, you won’t see the same benefits.
And that brings me back to the question of why some studies show reduced cancer risk from consuming broccoli but others have failed to do so. Differences in preparation methods between participants could make a big difference here. Think about it: if someone is boiling or roasting broccoli into oblivion (which is probably all too common), they might report eating the vegetable daily (and thus count as a high consumer), but not exhibit the expected benefits. We need to keep this in mind when interpreting this research.
This also means, of course, that if you personally are trying to get the most out of cruciferous vegetables like broccoli, you will want to cook them as little as possible. If you can’t handle brassica vegetables raw, steaming is probably your best bet. Or, you can eat sprouts (see below for more info on that).
Random Trivia & Weird News
🐌 A desert snail was glued to a specimen card for display at a museum. Four years later, museum staff realized that the creature was actually still alive.
Snails are perhaps best-known for their lack of urgency in all aspects of life. In fact, they are so committed to saving energy that they have evolved the ability to enter phases of suspended animation when confronted with hostile environmental conditions (such as excessive coldness or dryness). During this time, they curl up inside their shell and basically go into a deep sleep, requiring neither food nor water, until conditions become more favorable.
One of the most extreme examples of this phenomenon occurred back in 1846, when a desert snail from Egypt, presumed dead, was glued to an index card and put on display at the British Museum. In 1850, observers noted that the card appeared to be slightly damp. Intrigued, the museum staff applied some water around the shell, and the snail subsequently emerged, alive and well!
The museum specimen was immediately transferred to a glass jar, where he purportedly thrived for another two years, and even posed for the drawing shown below.
Image credit: From A Manual of the Mollusca (1851), by Samuel Pickworth Woodward
Random Trivia & Weird News
- Charles Serhan: Using specialized pro-resolving mediators to resolve inflammation. Via STEM-Talk.
- Euan Ashley: Exercise may be the single most potent medical intervention ever known. Via Ground Truths.
Products We Like
Seed sprouting kit
Decades ago, in a lab at Johns Hopkins, biochemist Jed Fahey analyzed different varieties of crucifers to determine which contained the highest concentrations of sulforaphane.
During this screening process, he discovered that broccoli is the best source of sulforaphane — specifically when it is only a few days old. Young broccoli sprouts contain an order of magnitude more sulforaphane than mature plants, and are by far the best source of the cancer-fighting compound in the natural world.
Nowadays, you can find broccoli sprouts pretty easily at grocery stores, but they’re expensive, especially on a per-serving basis. Fortunately, it’s ridiculously easy to sprout your own, using a kit like this one. Basically, you just pour some seeds into an inverted Mason jar, rinse them and drain them twice a day, and before the week is done you will have fresh sulforaphane-rich broccoli sprouts ready to go. You can check YouTube for more detailed breakdowns on how to do this successfully.
PS: If you’re looking for some good broccoli seeds, I’ve sprouted these successfully many times.
humanOS Catalog Feature of the Week
Fasting by Jeff Rothschild
This week, we’d like to highlight our Fasting course, developed by Jeff Rothschild. One of the biggest recent trends in nutrition has been intermittent fasting. And of course, there are new studies coming out all the time pointing to intriguing benefits for health, performance, and lifespan. But there are a few different styles of fasting - how do you determine which is best, in general and for you specifically?
In this course, Jeff explains different fasting protocols, and how to implement them in a way that works for your own life. We also suggest looking at our How-to Guide to Fasting if you’re seeking a quick reference sheet on the matter.
Wishing you the best,
