Many people are familiar with the term “cruciferous vegetables” and can even identify a vegetable like broccoli as belonging to this group. But because research on cruciferous vegetables has skyrocketed over the past three to seven years, many people are not familiar with the latest science on this age-old group of vegetables.
The name “cruciferous vegetables” is itself undergoing change! This group of vegetables was originally named for the four equal-sized petals in its flowers that could be viewed as forming a cross-like or crucifix shape. But many scientists are starting to favor the term “brassica vegetables” over “cruciferous vegetables” and the traditional name of this plant family in Latin, Cruciferae, is now being largely replaced by the Latin name Brassicaceae. (In Latin, the word “brassica” simply translates as “cabbage,” and cabbage is definitely a featured member of this vegetable group.)
You’ll also hear farmers referring to foods in this vegetable group as “cole crops.” The word “cole” (which is easy to spot in the word “coleslaw,” a dish usually made from cabbage but also from cruciferous vegetables like broccoli) once again takes us back to the Latin language; it comes from the word “caulis” that refers to the stalks of plants, especially to the stalk of the cabbage plant. (Interestingly, you can find this Latin root not in the cabbages that so commonly represent the broader family of cruciferous vegetables, but in cauliflower, which is another important member of this vegetable group.) Cruciferous vegetables are also sometimes referred to as the mustard family vegetables, since the widely popular mustard greens — and mustard seeds and mustard oils — also belong to this vegetable group.
The table below contains a comprehensive list of cruciferous vegetables that are commonly consumed as a part of cuisines worldwide:
- Chinese broccoli (Gai-lan)
- Chinese cabbage, Napa cabbage (Suey choy)
- Choy sum
- Collard greens
- Ethiopian mustard
- Field pepperweed
- Garden cress
- Land cress
- Mustard seeds, brown; green; white
- Rapini (Broccoli rabe)
- Rutabaga (Swede)
- Savoy cabbage
- Siberian kale
- Turnip root; greens
- Wild arugula
- Wild broccoli
- Wrapped heart mustard cabbage
The above list makes it clear that we should also be thinking about spices like brown mustard seed, yellow mustard seed, and horseradish as cruciferous vegetables, because they are! Health-supportive molecules like glucosinolates are concentrated in these spices in the same way that they are concentrated in the leaves of the plants (like mustard greens or horseradish greens).
Two especially common scientific groupings of cruciferous vegetables are the Brassica oleracea (broccoli, Brussels sprouts, cabbage, cauliflower, collards, kale, and kohlrabi) and the Brassica rapa (Chinese cabbage and turnips). Brassica campestris is another name for the genus-species grouping called Brassica rapa.
Conventional Nutrients in Cruciferous Vegetables
In terms of conventional nutrients (vitamins, minerals, proteins, carbs, and fats), we cannot find another vegetable group that is as high in vitamin A carotenoids, vitamin C, folic acid, and fiber as the cruciferous vegetables. As a group, the cruciferous vegetables are simply superstars in these conventional nutrient areas.
The vitamin K content of cruciferous vegetables — especially kale and collards — is fascinating to think about in light of intensive research over the past five years on cancer, inflammation, and cruciferous vegetables. Vitamin K is a conventional nutrient that clearly helps regulate our inflammatory response, including chronic, excessive inflammatory responses that can increase our risk of certain cancers. Studies on cruciferous vegetables and cancer prevention have not typically focused on vitamin K per se, but we suspect that the amazing K content of cruciferous vegetables is definitely related to their cancer-preventive properties through mechanisms involving better control of inflammation.
The astonishing concentration of vitamin A carotenoids in cruciferous vegetables and their unusually high content of vitamin C and manganese are clearly key components in their growing reputation as an antioxidant vegetable group. Scientific interest in the antioxidant function of the cruciferous vegetables has been sufficient to trigger funding of isotope studies on cruciferous vegetables that document the uptake of antioxidants in these foods from our digestive tract into our bloodstream. We’ve seen studies on 13C-labeled kale that show impressive bioavailability of beta-carotene, lutein, and retinol from this cruciferous vegetable. Significant increases in the blood levels of these key antioxidant nutrients have been seen very quickly in subjects who consume generous amounts of cruciferous vegetables in research studies. (“Generous” in one such study meant consumption of 3 cups of blanched, chopped broccoli during a meal.) The antioxidant richness of cruciferous vegetables has also been explicitly mentioned in several recent studies as one of the strong contributors to the risk-lowering impact of cruciferous vegetables on numerous forms of cancer.
One hundred calories’ worth of cruciferous vegetables (about 5-6% of a daily diet) provides about 25-40% of your daily fiber requirement! That fact shows what an incredible bargain cruciferous vegetable are when it comes to fiber. We suspect that it’s one of the reasons these vegetables have become increasingly prominent in research studies on diet and digestive support. We may not typically think about cruciferous vegetables when considering digestive disorders or risk of digestive tract cancers, but we should.
Two additional macronutrients — proteins and fats — also deserve special mention with respect to recent research on cruciferous vegetables. We tend to think about legumes, nuts, seeds, meats, dairy, and fish as the diet’s pre-eminent protein sources — as they are. But cruciferous vegetables can contribute a surprising amount of protein to the diet — over 25% of the Daily Value in 3 cups — and at a very low calorie cost. Two hundred calories of steamed broccoli will provide you with 20 grams of protein — not as much as the 30 grams in two hundred calories of roasted chicken breast — but still a very substantial amount. We suspect that the substantial protein content of cruciferous vegetables may contribute to their risk-lowering impact on certain cancers, partially due to their support of detoxification. (Especially during Phase 2 detoxification, certain amino acids found in protein are known to play a critical role.)
We are no more likely to think about cruciferous vegetables as pre-eminent sources of fat in the diet than we are to think about them as pre-eminent sources of protein. In particular, cruciferous vegetables don’t make many popular lists of omega-3 fats and their most important food sources. However, 100 calories’ worth of cruciferous vegetables typically gives us somewhere between one-third and one-half of a gram of omega-3 fat (333-500 milligrams). This omega-3 fat is primarily in the form of ALA (alpha-linolenic acid), which serves as the basic building block for all other forms of omega-3 fats in the body. There is actually far more ALA in 100 calories of cabbage than there is in 100 calories of salmon. While fish like salmon do contain most of their omega-3s in the form of EPA (eicosapentaenoic acid) or DHA (docosahexaenoic acid) rather than ALA, the amount of total omega-3s in 100 calories of cabbage (520 milligrams) is still substantial in comparison to the amount of total omega-3s in 100 calories of salmon (798 milligrams). The past 5 years of greatly expanded research on cruciferous vegetables and inflammation points to the omega-3 content of cruciferous vegetables as a potentially critical component of their unique health benefits.
Cruciferous Vegetable Phytonutrients
As impressive as they are in terms of their conventional nutrient content, cruciferous vegetables are even more renowned for their phytonutrients. During the past five years, cruciferous vegetables have largely taken over the world of research in the area of glucosinolates, phytonutrients that clearly have their headquarters in the cruciferous vegetable group. Thanks to research on cruciferous vegetables, scientists have now identified over 100 different glucosinolates in food, and without cruciferous vegetables in our diet, we simply cannot get optimal intake of the glucosinolates. What’s so special about glucosinolates is their potential for cancer prevention. Once converted into other molecules called isothiocyanates, the glucosinolates have an eye-opening track record in lowering the risk of certain cancers. The list below summarizes key glucosinolates found in cruciferous vegetables:
In our article, “Feeling Great with Cruciferous Vegetables,” we talk in detail about glucosinolates and explain exactly how they accomplish their cancer-preventive effects.
Understanding Differences between Raw and Cooked Cruciferous Vegetables
Recent research shows a definite dietary place for cruciferous vegetables in both raw and cooked form. Studies in this area have expanded in recent years, and scientists understand better than ever about the different paths taken by cruciferous vegetables when prepared in different ways. When consumed in raw form, it appears especially helpful for us to have freshly picked cruciferous vegetables. The greater potential benefits here involve enzymes. When cruciferous vegetables like broccoli are freshly picked (for example, within the previous 48 hours), their enzymes are much more likely to remain active. This better chance of enzyme activity — including activity of the enzyme myrosinase — gives us a better chance of having phytonutrients like glucosinolates converted into uniquely health-supportive molecules (like isothiocyanates). When consumed in fresh, raw, uncooked form, nutrients from the cruciferous vegetables that we eat are also more likely to be absorbed in the upper digestive tract, transported to the liver, and made available to other tissues in the body that might benefit from their presence.
When cruciferous vegetables are consumed in cooked form, and especially if they have not been allowed to sit chopped for several minutes prior to cooking, there is unlikely to be much enzyme activity (including myrosinase activity), and the digestive products of the cruciferous vegetables are more likely to pass through the upper digestive tract unabsorbed and continue down into the lower digestive tract (colon). At that point in the digestive process, the cruciferous vegetable nutrients are very likely to be further metabolized by bacteria. Some of the risk reduction seen for colon cancer following intake of cruciferous vegetables may be related to this passage of cooked cruciferous vegetable nutrient down through the digestive tract all the way to the colon without being absorbed. One way to increase availability of enzyme breakdown products in the upper digestive tract, however, is to chop raw cruciferous vegetables and let them sit in chopped form for several minutes prior to cooking. This process will allow myrosinase enzymes to go to work prior to their deactivation by cooking heats.
Eventually, researchers may be able to tell us the exact advantages and disadvantages for each consumption form of cruciferous vegetables (raw and cooked). In addition, researchers predict that we may one day understand how to match individual genetic tendencies with the best mix of cruciferous vegetables and the best balance of raw-versus-cooked consumption. At present, however, we can only conclude that both raw and cooked forms of cruciferous vegetables are very likely to have a place in optimal nourishment.
If we look exclusively at cooked cruciferous vegetables, however, and compare different cooking methods and their pros and cons, we will definitely find new information in the research that is well worth noting. First is the preference of steaming over microwaving. In a study that compared steaming versus microwaving of raw cabbage, researchers found that it took 7 minutes of steaming to result in the same about of enzyme (myrosinase) destruction that occurred with only 2 minutes of microwaving. In other words, short steaming was much better than microwaving for preserving some myrosinase activity in the cabbage. Researchers in this study also found higher concentrations of one particular isothiocyanate (AITC, or allyl-isothiocyanate) in lightly steamed cabbage, and for this reason they concluded that light steaming of cabbage might provide some unique health benefits. Steaming, of course, cooks foods at 212°F/100°C — a relatively low heat. We’re convinced that this relatively low level of heat was important in providing steamed cabbage with its higher AITC content. Along this same line of thinking, we’ve seen another cruciferous vegetable study showing successful delivery of glucosinolates in broccoli to a group of study participants in the form of broccoli soup. Like steamed cabbage, broccoli soup is likely to expose this cruciferous vegetable to a relatively low cooking temperature and help preserve desirable nutrients for this reason.
We’d like to make one final comment about preparation of foods in this cruciferous vegetable food group. Especially within the average U.S. diet, it’s difficult to find another food group in which as many different parts of the food are consumed. Within the cruciferous vegetable group, we commonly eat the flowers of the plant (for example, the broccoli florets), the leaves (for example, mustard greens, collard greens, turnip greens, and kale), the stems and stalks (for example, broccoli stems and stalks), the roots (for example, turnips or rutabagas or radishes), and the seeds (for example, mustard seeds). The unique benefits of this cruciferous vegetables food group may be partly related to inclusion of so many different plant parts in a cruciferous foods-including diet. Particularly when it comes to phytonutrients, plants distribute nutrients differently in their different anatomical parts. The fact that we commonly include so many different parts of cruciferous plants in our diet may help us broaden the diversity of phytonutrients that we get from this food group. Given this diversity of cruciferous plant parts, it’s also important to remember that different parts may require different cooking times for optimal nutrient retention.
Bitterness of Taste of Cruciferous Vegetables
From a chemistry standpoint, the taste of all foods is complicated. A wide variety of different substances contribute to the taste of any particular food. In addition, our individual biochemistry causes us to perceive taste differently, and the exact same food containing the exact same substances can taste extremely different to different people. In the case of cruciferous vegetables, however, a large percentage of individuals describe a certain bitterness of taste, and in research, this taste has been linked to a wide variety of phytonutrients, including glucosinolates, terpenoids, and flavonoids. Recent research has also linked the bitterness of taste in cruciferous vegetables with calcium content. Turnip greens, for example, which taste far more bitter to many people than cabbage, contain about 4 times more calcium than their fellow cruciferous vegetable. Although the commercial food industry has sometimes attempted to breed out bitter-tasting constituents from cruciferous vegetables (including sinigrin, one of the glucosinolates especially plentiful in cabbage), that practice does not make sense if we want to optimize our nourishment from this vegetable group. A much healthier approach would involve the blending of cruciferous vegetables with differently flavored foods in such a way that the cruciferous vegetables retain some of their natural and noticeable bitterness but within a blended-flavor context that makes the dish delicious!
Unique Nourishment from Cruciferous Vegetables: A Practical Summary
We are not aware of any food group that matches cruciferous vegetables for what we would call integrated nourishment across such a wide variety of nutritional categories. There are important amounts of macronutrients including fiber, protein, and omega-3s in this group. There are showcase amounts of many antioxidant, anti-inflammatory, and detox-related nutrients. Many B-complex vitamins are unusually concentrated in cruciferous vegetables, as are certain minerals. This food group also contains its own unique set of phytonutrients — the glucosinolates — that are simply unavailable to the same extent in any other food group. By commonly consuming all parts of plants from this group, including flowers, leaves, stems, stalks, roots and seeds, we allow this cruciferous vegetable group to integrate together an unusually wide range of nutrients that is broader than any other single food group subdivision in the average U.S. diet. For all of these reasons, and based on the latest research evidence, we cannot say enough about the healthiness of this food group for most every individual diet plan.
Source: World’s Healthiest Foods
Cruciferous Vegetables and Thyroid
Cruciferous Vegetables Thyroid Side Effects
One of the most common questions I get from patients is “does eating cruciferous vegetables cause thyroid problems?”
According to the research, it would take a large amount of cruciferous vegetables to cause hypothyroidism and it appears that there is only a risk if someone also has an iodine deficiency.
One study in humans found that the consumption of 5oz a day of cooked brussels sprouts for four weeks had no adverse effects on thyroid function.
So my advice if you have a thyroid issue is to consume cruciferous vegetables that have been cooked and keep them to about 1-2 servings daily.
Source: Dr. Axe
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Cruciferous vegetables contain glucosinolates and in a different area of the cell, an enzyme called myrosinase. When we blend, chop or chew these vegetables, we break up the plant cells, allowing myrosinase to come into contact with glucosinolates, initiating a chemical reaction that produces isothiocyanates (ITCs) – powerful anti-cancer compounds. ITCs have been shown to detoxify and remove carcinogens, kill cancer cells, and prevent tumors from growing.
Observational studies have shown that eating ITC-rich cruciferous vegetables protects against cancer – here are a few examples:
- Twenty-eight servings of vegetables per week decreased prostate cancer risk by 33%, but just 3 servings of cruciferous vegetables per week decreased prostate cancer risk by 41%.
- One or more servings of cabbage per week reduced risk of pancreatic cancer by 38%.
- One serving per day of cruciferous vegetables reduced the risk of breast cancer by over 50%.
Source: Dr. Fuhrman
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Before You Eat Kale, Cook It
Cruciferous vegetables, also known as brassicas, can include kale, broccoli, cabbage, cauliflower, bok choi, arugula, turnips, and watercress. If you want the health benefits of kale without the aspects that could lead to an enlarged thyroid, simply cooking it can mitigate this risk. The goitrogenic properties of kale (the aspects that contribute to an enlarged thyroid) tend to dissipate when kale or other veggies are cooked.
Making sure to mix up which vegetables you eat will also ensure that you are receiving all those vegetable nutrients without overdoing it. Some other vegetables that are non-goitrogenic are cucumbers, beets, celery, parsley, zucchini, and carrots.
And don’t let all this thyroid talk prevent you from eating your greens. Teresa Fung, an adjunct professor of nutrition at the Harvard School of Public Health and a professor at Simmons College in Boston, told WBUR that “normal, reasonable amounts of eating should not be a problem. A regular person [with no thyroid issues] who eats several servings of cruciferous vegetables a week should not have problems.”
However, Fung does note that it’s all about moderation. “It’s the dose that makes a poison,” she told WBUR. “If people have hypothyroidism or they’re taking thyroid medication, then they should check with their doctor. But even in this case, reasonable amounts shouldn’t be a problem. Now, if people have a tall glass of kale juice every single day, then it gets into the unknown territory.”
Source: Medical Daily
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Iodine and thyroid function
Very high intakes of cruciferous vegetables, such as cabbage and turnips, have been found to cause hypothyroidism (insufficient thyroid hormone) in animals (68). There has been one case report of an 88-year-old woman developing severe hypothyroidism and coma following consumption of an estimated 1.0 to 1.5 kg/day of raw bok choy for several months (69). Two mechanisms have been identified to explain this effect. The hydrolysis of some glucosinolates found in cruciferous vegetables (e.g., progoitrin) may yield a compound known as goitrin, which has been found to interfere with thyroid hormone synthesis. The hydrolysis of another class of glucosinolates, known as indole glucosinolates, results in the release of thiocyanate ions, which can compete with iodine for uptake by the thyroid gland. Increased exposure to thiocyanate ions from cruciferous vegetable consumption or, more commonly, from cigarette smoking, does not appear to increase the risk of hypothyroidism unless accompanied by iodine deficiency. One study in humans found that the consumption of 150 g/day (5 oz/day) of cooked Brussels sprouts for four weeks had no adverse effects on thyroid function (70).
Although many organizations, including the National Cancer Institute, recommend eating a variety of fruit and vegetables daily (serving number depends on age, sex, and activity level), separate recommendations for cruciferous vegetables have not been established. Much remains to be learned regarding cruciferous vegetable consumption and cancer prevention, but the results of some epidemiological studies suggest that adults should aim for at least five weekly servings of cruciferous vegetables.
Source: Oregon State University
Cruciferous Vegetables and Irritable Bowel Syndrome (IBS)
Why do Cruciferous Vegetables produce Gas in those with IBS?
So why do cruciferous vegetables produce so much gas? It all has to do with sulfur. Yes, I’m talking about that chemical compound found on the periodic table that you had to learn back in grade nine science class. Foods high in sulfur get broken down in the large intestine and produce hydrogen sulfide, which is also known as “the rotten egg smell.” Not only do high sulfur foods lead to more gas, but also very smelly gas.
Cruciferous vegetables contain an oligosaccharide (carbohydrate chain composed of 3-9 simple sugar molecules) called raffinose. Humans do not have the enzyme to break down raffinose, so it passes through the stomach and small intestine undigested. One of the primary roles of the large intestine is to absorb the nutrients that are broken down in the stomach and small intestine. So when food enters the large intestine undigested, this is where symptoms can happen.
The large intestine is full of bacteria that don’t normally cause problems. However, when these bacteria are given undigested food, like the above mentioned raffinose component, they ferment (bacteria chemically breakdown substances) them. One of the byproducts of bacterial fermentation is gas, which leads to flatulence and bloating. Those with IBS and other digestive disorders can experience visceral hypersensitivity. Visceral hypersensitivity means that the nerves in the lining of their intestine are extra sensitive. That extra gas production we talked about is enough to cause painful bloating, gas and discomfort in those with IBS.
What To Do?
It’s a good idea to avoid high sulfur vegetables, especially if you have IBS, even for just a short period of time. Then you can add them back in one at a time to see if they cause you digestive symptoms. But what if you’re an avid broccoli fan? Or just absolutely love Brussels sprouts? Here are a few tips and suggestions to avoid the unwanted symptoms of cruciferous vegetables and still include them in your diet.
- Simmer, sauté, bake, or steam! When you cook vegetables they are easier to digest. Make note of whether or not you still experience symptoms and the severity. Cooking these vegetables or having pureed like in a soup may reduce symptoms.
- Start off slowly. Once you’ve eliminated these vegetables, you’ll want to add them back in eventually. Before eating a big portion of a cruciferous vegetable, try a small amount, like ½ a cup. You may be able to tolerate small amounts well but have symptoms with larger amounts. Increase your serving size each time you try it to see what your body can handle.
- Explore new vegetables! It may be time to expand your taste buds… Look for recipes online that look delicious and can help you enjoy low sulfur vegetables such as squash, eggplant, bell peppers, green beans or kale.
Source: Stephanie Clairmont
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Source: Cleveland Clinic