by Dr Rupy Aujla16 Mar 2023
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Broccoli and other cruciferous vegetables were identified as important contributors to a health-supporting diet.
It’s hard to say: Studies do not always define what corresponds to a higher intake and consumption levels vary across studies. Two studies found positive results for 400 g per week. (Armah et al. 2015)
Our advice: Get your daily dose by adding at least one portion of cruciferous veg to your plate each day. One 80g portion of broccoli is roughly 8 florets. Diversify between all the types available!
Contradictory results remain and observational studies are limited by many factors. We need more research to really understand the benefits of cruciferous vegetables on human health.
Our take on the data: This is the best data currently available. When we look at the overall evidence, including laboratory studies, potential mechanisms and studies about eating patterns and vegetables in general, we can strongly suggest that cruciferous vegetables in our diets are likely to be supporting our health.
What makes cruciferous vegetables so special anyway?
Some of these potential benefits can be attributed to the myriad of nutrients and plant compounds in purple-sprouting broccoli.
Purple broccoli contributes to our dietary fibres, vitamins, especially C, K and B9 and minerals, especially iron and calcium.
As a cruciferous veggie, broccoli is known for its glucosinolates. They’re a unique group of compounds that get converted to isothiocyanates, after being chopped or chewed. You also find them in kale, cabbages, brussel sprout, bok choy and more. Although more than 130 glucosinolates have been identified in plants, glucoraphanin, sinigrin and glucobrassicin are the main glucosinolates in commonly consumed brassica vegetables. They are broken down into various phytochemicals with biological activities, such as sulforaphane, phenethyl isothiocyanate (PEITC), indole-3-carbinol (I3C) and 3,3′-Diindolylmethane (DIM). Check out their chemical structures:
Chemical structures of the breakdown products sulforaphane, PEITC, I3C and DIM. (Melim et al. 2022)
Bitterness from cruciferous veggies may not be the same for everyone. Humans have 25 different types of bitter taste receptors, compared to just one sweet receptor, allowing us to detect a wide range of bitter compounds. But genetic differences in a gene encoding these receptors, called TAS2R38, can impact their function and our perception of bitter tastes. (Zhao et al. 2022)
Quick genetics: We all inherit two versions, or alleles, of the TAS2R38 gene, encoding a bitter taste receptor. Depending on the gene variants we inherit, our sensitivity to bitter taste from certain compounds varies.
(1) Bitter-insensitive: Those with two copies of the nonfunctional variant called AVI aren’t sensitive to bitter tastes from certain compounds (genotype AVI/AVI).
(2) Bitter-sensitive: Those with one copy of the AVI variant and one copy of the functional variant called PAV perceive the bitter taste of these chemicals (genotype AVI/PAV).
(3) Super-tasters: Those with two copies of the PAV variant taste bitter elements intensely (genotype PAV/PAV).
Knowing why you may taste some vegetables extra bitter can motivate you to find ways to make them tastier by stimulating other taste receptors with spices or food pairings.
The physiological benefits of cruciferous vegetables are not only dependent on the amount and frequency of consumption, but also on the activity of a hydrolyzing enzyme, called myrosinase. It breaks down glucosinolates into isothiocyanates, which are highly bioactive compounds.
There are substantial interindividual variations in the extent of conversion of glucosinolates to isothiocyanates and their resulting absorption and bioactivity. This variability is sufficiently large that it most frequently disrupts the ability of clinical trials utilising diverse populations to determine the significance of any effects.
We’re often told that cooking may alter the benefits we get from certain plants. But it’s not that simple – some compounds may increase after cooking, others may decrease and the cooking method also matters. Comparing the benefits of raw and cooked vegetables is complicated and many mysteries remain. More than that, our inner ecosystem can play a role.
The cruciferous family of vegetables are unique in their prevalence of glucosinolates. These compounds are inert and need to be broken down in order to be useful to our bodies. That’s where myrosinase comes in. It’s found in the tissue of cruciferous plants and helps to break down glucosinolates into bioactive compounds, such as isothiocyanate and indoles.
When we eat cruciferous vegetables raw, myrosinase is released as we chop, chew, or cut them and gets to work, breaking down glucosinolates as they go through the upper digestive tract.
Cooking tends to damage myrosinase, hampering its ability to break down glucosinolates. How much is lost depends on how we cook the vegetables, at what temperature and for how long. But we cook food for flavour, texture and ease. Thankfully, that’s not the end of the story…
Gut microbes have our back: The conversion of glucosinolates to their bioactive products can also occur from gut microbes. When myrosinase is inactivated, glucosinolates from cruciferous veggies transit intact to the colon, and are broken down by the gut microbiota. They form isothiocyanates and other bioactive compounds that can be absorbed and used by the body.
So, the human microbiome can have a significant impact on increasing the bioavailability of glucosinolate derivatives. This partnership between plant compounds and gut microbes explains why some people may derive different health benefits from the same diet.
Reminder: A healthy gut microbiome is a gut ecosystem that is well balanced, with higher microbial diversity. Eating lots of plant fibres from vegetables, fruits, nuts and legumes is an important contributor to nurturing our gut microbiome.
If this still sounds like gibberish, here’s a figure to help you make sense of the role of gut microbes in activating glucosinolates 👇
Eating more vegetables and diversifying is the core priority, aiming for 3 portions in every meal. Alternating between raw and cooked could be a good way to get more bioactive compounds, but only if you enjoy it.
What happens next? How can these compounds act in the body?
The cruciferous family of vegetables, which includes broccoli, brussels sprouts, cabbage, and kale, are unique in their near-ubiquitous prevalence of glucosinolates.
We talk about the beneficial effects of cruciferous vegetables on health and preventing chronic diseases. But how does it actually work? How could eating a green veggie influence how we feel in the short and long term?
These are big questions that are being researched by scientists all over the world. Laboratory studies on animal and cell models suggest several potential ways through which cruciferous vegetables like broccoli and kale may act in the body. Let’s look at some of them.
Apoptosis is the primary mechanism that plays an essential role in balancing cell growth and cell division to prevent cancer. Bioactive compounds in cruciferous vegetables, such as flavonoids and isothiocyanates, have been found to trigger apoptosis in various ways.
(1) Sulforaphane can inhibit the activity of histone deacetylases, which increases the expression of pro-apoptotic factors, such as Bax, Bad, and p21, and subsequently apoptosis.
(2) Another way could be by blocking the PI3K-Akt signalling pathway, leading to the inhibition of cell proliferation and the induction of apoptosis in tumour cells. (Bayat Mokhtari et al. 2018; Melim et al. 2022)
Bioactive compounds from cruciferous vegetables are suggested to decrease chronic inflammation. For example, sulforaphane may prevent the activation of receptors involved in inflammatory responses, like toll-like receptors. In turn, it prevents the activation of inflammatory signalling pathways like NF-κB and prevents the expression of inflammatory-related genes, such as TNF-alpha and interleukins.
Isothiocyanates from cruciferous vegetables may induce NRF2 signalling, which regulates the expression of antioxidative proteins.
How: They can interact with a protein called Cul3, which allows Nrf2 to be released and travel to the nucleus of the cell to activate various genes, including those coding for antioxidant proteins. These antioxidant proteins act to reduce reactive oxygen species levels, protecting cells.
Evidence: Many animal and cell-based studies have reported that purified isothiocyanates or brassica diets increase Nrf2-dependent antioxidant gene expression.
But that’s not all: Nrf2 pathways also regulate genes involved in cytoprotection, chemoprevention, and inhibiting the overproduction of proinflammatory cytokines.
The activation of Nrf2 pathways by isothiocyanates may also activate various phase 2 detoxifying genes. These include NAD(P)H quinone reductase 1, glutathione transferases, and heme oxygenase 1. They enhance the detoxification of environmental carcinogens.
Through an indirect preventive manner, the ingestion of cruciferous vegetables may improve the flora composition of the gut microbiota. Maintaining the intestinal microbiome’s homeostasis is vital to prevent chronic inflammation, dysbiosis and carcinogenesis.
How: By acting as prebiotics used as substrates by gut microbes to form beneficial compounds, such as short-chain fatty acids and phytochemicals with bioactivity.
Their chemical structure allows them to bind to specific proteins in the body and activate or inhibit them, which can trigger some of the various biological responses we talked about. For example, computer modelling predicts that sulforaphane is a good fit for the active site of targets like histone deacetylases. (Bayat Mokhtari et al. 2018)
Cancer prevention: Colon Tse et al. Nutr Cancer. 2014; Breast Liu X et al. The Breast. 2013; Ovarian Han et al. Diagn Pathol. 2014; Gastric Wu et al. Cancer science. 2013; Pancreatic Li et al. World J Surg Onc. 2015; Lung Zhang et al. Molecular nutrition & food research. 2018; Bladder Yao et al. Cancer Causes Control. 2014
Mental Health: LaChance & Ramsey, 2018