Cruciferous vegetables – what are they and are they good for me?

Did you know that rocket (arugula) is in the same vegetable family as cabbages or turnips? These veggies are part of the Brassicaceae family which in turn is part of the Cruciferous genus.

Cruciferous vegetables are one of the dominant food crops worldwide and include broccoli, brussel-sprouts, cabbages, turnips, watercress, collard greens, mizuna, radishes and wasabi (any many more).

Cruciferous flowers are shaped like little crosses. Photograph source: http://www.themicrogardener.com/wp-content/uploads/2011/07/Rocket-flowers.jpg

The flowers of the Cruciferous family(CF) resemble little crosses – that’s why they are called Cruciferous.

All Cruciferous vegetables contain loads of vitamins, minerals and phytochemicals and are really good for us.

Why are the phytochemicals in Cruciferous vegetables so good for me?

Even plants don’t like being attacked, so all plants have defence mechanisms to protect them from being eaten by pests or getting diseases. These include direct methods using spines or thorns or indirect methods like phytochemicals.

The sulphur-based phytochemicals within Cruciferous vegetables are called glucosinolates (of which there are many different types – at least 120).

Glucosinolates are responsible for the bitter taste of most Cruciferous vegetables and the more bitter the taste – the higher the levels of glucosinolates.

This is where it gets a bit complicated – these plants use the chemical reaction between Glucosinolate and an enzyme (Myrosinase) (which co-exist but are segregated) to discourage anyone/thing who wants to eat them – it makes them taste really bitter and may discourage pests. who want to eat it. This in turn, provides many health benefits for us.

As soon as plant/leaf is chewed or cut by us, it causes the Myrosinase enzyme to convert Glucosinate to the biologically active compounds called isothiocyanates.

Bugs or other animals eat the plant raw however we tend to cook these vegetables prior to eating. Myrosinase is inactivated by heat and stomach acid so it may not be able do its complete conversion job.

Radishes are great – we eat them raw and get their full nutritional benefits

What are these biologically active compounds and how do they work?

We have all heard that a diet high in fruit and especially vegetables helps to protect our bodies from disease and improve our overall health.

Research has suggested that isothiocyanates may help protect cells and reduce the risk of developing cancer. This may be due to the role isothiocyanates play during metabolism of toxins within the liver.

The liver uses two phases convert toxic compounds to less harmful water soluble metabolites that are able to be excreted.

  • Phase I breaks down substances like toxins, pharmaceutical drugs and hormones into intermediate metabolites (may include reactive oxygen species (ROS)).
  • Reactive products of phase I (e.g ROS) may damage cells if they are not converted by phase II enzymes like glutathione to less harmful metabolites that are water soluble and able to be excreted.
  • Cruciferous vegetables help support phase II by providing the nutrients required for the synthesis of glutathione, which is one of the more important antioxidants in the body.

Please have a look at reference (1) for more information about the protective affects of Cruciferous vegetables.

So what can we do to ensure we get the health benefits from these vegetables?

Please note that some of the unconverted Glucosinolates that reach the intestine may be converted by gut bacteria, however not as much via the enzyme activation via chewing. Gut conversion may differ due to variations in gut bacteria.

My tips are:

  • Raw vegetables like coleslaw, watercress, radish are ok because they are not cooked and will be activated while chewing.
  • If I am going to cook my vegetables, I try to cut them up ahead of time to allow the enzyme to well and truly do its job, say 5-10 minutes. I cut into smallish pieces to expose more cut surfaces.
  • I lightly steam my vegetables and leave a little bit of crunch. This may mean that less of the Myrosinase is destroyed.
  • Using the whole vegetable in a smoothie or juice is a great way to get the most out of these vegetables. Try to use a juicer that allows some of the pulp to remain in the liquid.
  • We will still get some benefit after cooking, however the bioactive compounds will be reduced and are dependant on gut bacteria conversion.

There are some cautions to consider when consuming Cruciferous vegetables.

  • High levels of soluble fibre may cause abdominal discomfort due to fermentation in the large intestine (increased levels of gas).
  • Consumption of high levels of Cruciferous vegetables may lead to thyroid issues due to the goitrogenic effects. May be more of a problem for iodine deficient individuals. Goitrogens = substances that disrupt the production of thyroid hormones by interfering with iodine uptake in the thyroid gland.
  • Some people might find the bitter taste of some Cruciferous vegetables unpleasant.
  • The benefits of Cruciferous vegetable are different for everyone and also the nutrients in these vegetables are dependant on soil quality, how long ago they were harvested and the method of cooking.
  • Cruciferous vegetables (like many leafy green vegetables) are high in vitamin K. Those people taking anticoagulant medications like Warfarin should discuss intake with their doctors.

References

  1. Talalay, P & Fahey JW 2001, Phytochemicals from cruciferous plants protect against cancer by modulating carcinogen metabolism, https://www.ncbi.nlm.nih.gov/pubmed/11694642
  2. Gregor, M, How to Cook Broccoli 2016, https://nutritionfacts.org/2016/02/09/how-to-cook-broccoli/

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