Should we eat Brussel sprouts all year round?
Christmas is over for another year, and it might be with a sigh of relief, or regret, that you bid farewell to the infamous Brussel sprout...
Love them or loathe them, we all have our own opinion on that festive staple, but there's more to this humble little vegetable than meets the eye. While many of us are repulsed by their slightly bitter flavour; a taste which is in fact an act of chemical warfare against your taste-buds designed to deter all of you would-be diners, these tiny veggies actually pack a considerable health-punch.
Brussel sprouts, like broccoli, cress and cauliflower, are a type of cruciferous vegetable. Studies have shown a diet rich in cruciferous vegetables to be important in maintaining human health. To start with, they are highly nutritious and a rich source of fibre, minerals and vitamin C. However, some of the most exciting health benefits associated with these vegetables are from what are known as secondary metabolites: these are compounds found in the plant not actually needed for growth, nutrition or even keeping us alive. Brassica (the family of plants to which sprouts belong) are particularly rich in one type of these secondary metabolites known as glucosinolates.
Eat your greens
The astounding health benefits associated with a high-brassica diet are almost entirely attributed to one glucosinolate in particular - glucoraphanin. Glucoraphanin has been shown to act upon the life-sustaining chemical reactions that allow our cells to grow, reproduce, and respond to their environments. This is the web of organised chaos broadly termed 'cell metabolism'.
When you chew sprouts, you break up their cellular structure, releasing the glucosinolates packaged inside. The glucosinolates can then come into contact with plant enzymes known as myrosinases which were previously stored separately inside the cell. The plant myrosinase acts to break down the glucoraphanin into a compound called sulforaphane; this is what makes the magic happen.
The sulforaphane travels down your throat, through your stomach, and then to your intestine where it is absorbed into the body. Once absorbed, sulforaphane acts initially to cause a small amount of oxidative stress. Oxidative stress occurs when the levels of highly reactive, oxygen-containing compounds (known as free radicals) are higher than the body's ability to destroy them or counteract their harmful effects. This causes no lasting damage to healthy cells which are capable of recovery, but can kill cancerous cells which are already too damaged to self- repair, making sprouts and their cruciferous cousins very interesting to cancer research groups, although human studies have shown mixed results. The initial bout of oxidative stress also stimulates healthy cells' detoxifying enzymes which act to deactivate reactive oxygen species which would otherwise cause damage to DNA and proteins.These health benefits come, for some, at a bitter, smelly cost.
The good, the bad and the pungent
Glucosinolates are not only responsible for the outstanding health benefits of brassica, but also for their distinctive taste. Even by the standards of brassica, Brussel sprouts possess a particularly strong flavour - this is attributable specifically to another glucosinolate known as sinigrin. The more sinigrin present within the vegetable, the more bitter they taste, and consequently the stronger our aversion.
In response to our repugnance, food companies have used classical plant breeding techniques to reduce the amount of sinigrin produced in our sprouts, making them taste more palatable. They have done this by selectively breeding plants lacking GS-ALK, the enzyme which produces the compound from its tasteless precursor. This genetic selection has had a secondary effects unbeknown to the producers of the time; this effect is now, through advancements is scientific techniques, being understood to have the potential to improve human health. GS-ALK is also responsible for the conversion of glucoraphanin to gluconapin. By eliminating the activity of this enzyme, plant breeders have accidentally caused an increased accumulation of glucoraphanin. Consequently, Brussel sprouts are not only becoming milder, but also potentially healthier.
Could we engineer 'super sprouts'?
A few years ago a 'super broccoli' with three times higher levels of glucoraphanin was released on sale in the UK, reported to help prevent certain cancers. So could we see the same thing happen with sprouts?
Professor Richard Mithen of the Institute of Food Research is a no stranger to the development of functional foods. As developer of high-glucosinolate broccoli and self-confessed brassica fanatic, Richard knows a thing or two about what makes food 'super'.
"Brussel sprouts are really unique amongst brassica because of their wide range of genetic diversity. This makes it genetically selecting for a high-glucoraphanin cultivar potentially easier." Says Professor Mithen. "This is something you don't get with broccoli so we had to look hard for it."
I don't like Brussel sprouts. Can't I just take a sulphoraphane pill?
In theory, taking the bioactive in pill form would be an easy way to deliver a standardised sulforaphane dose to those who still can't stand the sulphurous taste of sprouts. However, as is the case with many bioactive compounds, we are far from being able to simply pop a functional pill. It's key to remember that glucosinolates aside, brassica vegetables contain many other healthy compounds such as dietary folate and fibre, all of which could never be substituted in any cocktail of capsules. Pharmacological logistics aside, demand for the vegetable remains high with the UK alone consuming 9875 tonnes of sprouts over the festive period each year. Any empty spaces at a table once full are always a saddening sight - perhaps we are not yet ready to say goodbye to our forlorn festal friend? So, in the spirit of the season, let's look forward to another merry Christmas full of good-cheer and glucosinolates.
Does it make a difference how I cook my sprouts?
Given the recent good press surrounding glucosinolates, it's becoming easier and easier to view sprouts as a satiating snack than the soggy side-dish of Christmas past. Often, sprouts are over-boiled leaving them feeling mushy with an unappealing pallor - rather like grandma after a little too much sherry. The way cruciferous vegetables are cooked can severely affect their glucosinolate content. When sprouts are boiled, up to 90% of the glucosinolates within them leach out into the cooking water and are wasted. Studies have shown that steaming them, microwaving them, or even stir-frying them can preserve the glucosinolates, making a snack so delicious you'd barely know it was good for you.
Can you recommend any recipes to help me incorporate more sprouts into my diet?
Sprout Slaw - yes they're delicious (and healthy) raw!
Prep time: 25 minutes
o 1 tablespoon grainy mustard
o 3 tablespoons white-wine vinegar
o 2 teaspoons honey
o 2 tablespoons olive oil
o Salt and pepper
o 1 pound brussels sprouts, trimmed and shredded
o 1 small head radicchio, cored and thinly sliced
o 1/2 cup chopped fresh chives
o 1/4 cup toasted sunflower seeds
In a large bowl, whisk together mustard, vinegar, honey, and oil. Season with salt and pepper. Add Brussel sprouts, radicchio, chives, and sunflower seeds and toss to combine.
Spicy Sprout Stir-fry
Prep time: 20 minutes
o 500g Brussels sprouts, trimmed and halved
o 1 tbsp sunflower oil
o 1 chilli, sliced into rings
o 2 garlic cloves, finely chopped
o large piece of fresh root ginger, cut into fine matchsticks
o 1 tbsp soy sauce
Steam the sprouts for 6 mins. Heat the oil in a wok, then stir-fry the chilli, garlic and ginger for 1 min. Add the sprouts, cook for 2 mins, then drizzle with the soy sauce. Give everything a final toss before serving.
Are you totally sold on the benefits of brassica? Of course you are. However, even the most devoted missionary for metabolic health must enjoy cruciferous vegetables as part of a balanced diet, incorporating all five major food groups and the occasional festive treat!