Although once only grown as a winter feed for cattle, kale has thankfully undergone some impressive rebranding and has been propelled to the dizzy heights of ‘superfood’ for a while now, popping up in everything from green juices, smoothies, salads . . even puddings! But why all the fuss? What is it that makes kale such a nutritious vegetable?
Well, firstly, just one generous handful of raw kale will give you all of your vitamin A and K for the day (although as these are fat soluble vitamins, try to eat a source of fat alongside the kale, like almonds in your smoothie or an olive oil dressing on your salad, for optimum absorption) (1). These vitamins are vital for the maintenance of healthy skin, eyes and normal blood clotting. This much kale can also provide the vast majority of your daily vitamin C, as well as other important disease-preventing phytonutrients like beta-carotene and lutein (1). Lutein, alongside vitamin A, helps to maintain normal vision, especially in dim light, and may also help reduce the risk of age-related eye problems in the future (2). So it’s not just carrots that help you see in the dark!
Cooking often destroys nutrients in vegetables, but it seems that this is not so much the case with kale. Although blitzing raw kale into a smoothie is delicious, and still packs a nutritional punch, steaming kale actually increases the total levels of beneficial compounds called phenolic acids (which are antioxidants). This is probably because gentle cooking helps to break down the tough tissues and cell walls of the vegetable, allowing us to fully extract the goodness from each and every cell (3).
Although as you will probably know by now, I really don’t believe in counting calories, it is certainly true that filling up on low-energy density foods like kale and other green leafy veg can help you to maintain a healthy weight. This is because their water and fibre content will help to keep you feeling fuller for a long time, and can therefore make it easier to avoid snacking in between meals. It is also near impossible to overindulge on kale. It is an ingredient, like many other vegetables, that you can really enjoy in abundance, so there is no need to feel like you are ever denied a fully satisfying meal.
As ever, a small word of note . . .
Kale and the thyroid. What’s the connection?
There have been some concerns raised recently about whether kale can contribute to problems with the thyroid, so I thought I would try to clarify the facts on this matter.
All cruciferous vegetables (cabbages, spinach, pak choy, kale etc) contain compounds called glucosinolates, which are generally considered to be a good thing, particularly in the prevention of certain types of cancer, including thyroid cancer (4)(5). However, almost 100 years ago, scientists noticed that if you fed animals excessive amounts of cruciferous vegetables, the normally beneficial glucosinolates then reduced the animal’s ability to absorb and incorporate iodine into their thyroid glands. These studies seem to be where the current concerns have stemmed from.
A little more about iodine – the real culprit here . . .
Iodine is crucial for us to make thyroid hormones, but as we cannot make iodine in our bodies, it has to come from our diet. In humans, a long-term, severe deficiency of iodine can result in a goitre. This is a swelling of the thyroid, located in the front of the throat, which increases in size in an effort to try to ‘trap’ enough iodine to keep up its normal function. It is, thankfully, very rarely seen in the UK.
The more subtle effects of a lack of iodine may include low thyroid hormone levels, or hypothyroidism; this is still a rare cause of the condition, and iodine is therefore not routinely measured in the UK when testing for thyroid problems. This is because most people who eat a balanced and varied diet are highly unlikely to have any issue with their iodine levels, as it is easy to get a plentiful supply if you consume fish, dairy products*, iodised salt (not sea salt) or seaweed.
However, iodine concentrations in plant-based foods (other than seaweed) are fairly low, which can mean that some vegetarians, and particularly vegans, are at a higher risk of deficiency. In one study, up to 80% of vegans had low levels (6). This insufficiency of iodine overall is arguably more of an issue with regards to thyroid function, than the potential effects of cruciferous vegetables.
So, should we just eat more seaweed then?
A word of warning about seaweed: brown seaweeds, such as kelp, and some seaweed supplements, are often a very highly concentrated source of iodine, and therefore can give you excessive amounts if eaten more than once a week. As always, too much is as bad as too little, so do read the labels! You should definitely avoid having more than 600 micrograms/day – the recommended daily intake is about 150 micrograms per day – plenty enough to help make all the thyroid hormones that you need! (7)
Iodine is also extremely important for a developing infant, so ensuring that you have adequate amounts in your diet during pregnancy (and ideally beforehand) is a great idea, especially if you are vegan. Pre-natal vitamin supplements often include iodine, so do check the label, and speak to a healthcare professional if you have concerns (7).
Back to the vegetables…
So, although there is a hypothetical link that cruciferous vegetables may block iodine uptake into the thyroid, which may possibly then lead to hypothyroidism, this effect is yet to be well established in humans. The link, however, is likely to be almost eliminated if there is enough iodine in your diet anyway. These possible effects, however, may be accelerated if you consume a very large amount of raw cruciferous vegetables regularly, such as in green smoothies or juices over a prolonged period of time. Cooking reduces glucosinolate action (8). This case study gives an example of the amounts of raw veg we are talking about.
Symptoms of hypothyroidism: tiredness; intolerance of the cold, or always feeling cold; difficulty concentrating, remembering; constipation; very dry skin; reduced appetite, but weight gain. If you are concerned that you may be suffering from this condition, make an appointment to see your GP for a consultation and blood test:
So what is the bottom line?
- Keep eating kale (and all the other cruciferous vegetables for that matter). It has multiple health benefits that far outweigh these small risks for most people, and therefore it is important to keep things in perspective!
- Ideally, try to make sure it is organic as much as possible as kale can have quite high levels of residue from crop spraying (pesticides, herbicides etc.). Eating it in moderation, even if that is a small amount everyday, is absolutely fine. Just avoid kilos of it raw, including in juices or smoothies.. (9)
- Do ensure that you have some good sources of iodine in your diet, especially if you are vegan. However, try not to rely too heavily on iodised salt as your source, as it is still salt after all. Adequate iodine intake offers protection against the possible effects from veggie glucosinolates on your thyroid.
- It is still fine to eat cruciferous vegetables if you are hypothyroid already.
- Remember, as always, too much of a good thing can become a bad thing eventually. Even water is dangerous in high enough volumes! This is just another example.
(See references below)
So, here are my 3 delicious things to do with kale:
Why not try having a go at the recipes below for some new ideas of how to add this super nutritious vegetable into your meals this week? It comes into the best of its season around mid-late winter, so now is the perfect time to enjoy a little more in your life. All hale the kale!
Spiced Chickpea, Kale & Squash (or Pumpkin) Salad
This is a hearty salad, packed with flavour and goodness. It takes a little time to prepare but is a meal in itself. The crunchy parsnip fries on top make it a bit special, but if you’re pushed for time, skip them.
You’ll Need (Serves 3-4)
- Butternut squash or half a pumpkin, roughly 500g, sliced or diced
- Coconut oil
- 1 tin chickpeas, drained
- 1 tsp cumin
- ½ tsp smoked paprika
- ½ chilli powder
- ½ tsp salt flakes
- 1 tsp raw honey
- 150 bag of kale, large stalks removed
- Juice of one lemon
- 1 clove garlic, crushed
- 2-3 tbsp extra virgin olive oil
- 1 large parsnip, spiralised or cut into very thin strips
- Coconut oil for frying
- 2 tbsp tahini
- Juice of one lemon
- 2-3 tbsp water
- Pre heat oven to 200C fan.
- Drizzle the pumpkin with oil and roast in the oven for 25-30 minutes or until browned on the edges and cooked.
- Toss the chickpeas in a bowl with cumin, paprika, chilli powder, salt and honey, a splash of oil. Spread them on a tray and add to the oven for 15 – 20 minutes, shaking occasionally. Leave chickpeas to cool on the tray and they will crisp up.
- Combine the lemon juice, garlic and 2-3 tbsp olive oil and massage into the kale with your hands in a large bowl for 3-4 minutes until it begins to shrink in volume and is glossy all over.
- In a small heavy pan melt enough coconut oil to cover and fry off the parsnip until golden brown, leave to drain on a kitchen towel.
- Mix the tahini and lemon juice, it will thicken up and add enough water to get a smooth just pourable paste.
- Assemble, top with the parsnip fries, and drizzle with the tahini dressing.
Kale & Bean Soup with Pistachio & Lemon Pistou
This is a clean and simple kale soup that holds its own alone but comes alive with a tangy fresh pistachio and lemon pistou stirred in.
You’ll Need (Serves 6)
- 1 tbsp coconut oil
- 1 large onion, diced
- 3 carrots, chopped
- 3 clove garlic, crushed
- 500ml chicken or vegetable stock
- 700ml water
- 1 medium sweet potato, small diced
- 1 cm fresh ginger, peeled and grated (10 grams)
- 4 big sage leaves
- 3 sprigs fresh thyme
- 2 tin cannellini beans, drained
- 1 courgette, cut in large batons
- 150g kale, stalks removed, chopped
For the Pistachio and Lemon Pistou
- 80g raw pistachios
- 2 small clove garlic
- 50g basil or parsley
- 1 lemon, juice and zest
- 2 tbsp olive oil
- 2 -3 tbsp water
- In a large pan, fry the onions and carrots in the coconut oil for 5-6 minutes until softened then add the garlic for 1-2 minutes more.
- Add the stock, sweet potato, ginger, herbs and beans, cover with water and bring to the boil, simmer for 5 minutes then add the courgette and kale and simmer for another 10 – 15 minutes, until cooked. Season to taste.
- Meanwhile in a small blender make the pistou by whizzing up all the ingredients, adding the water at the end, season to taste.
- Serve with a big dollop of pistou on top.
Green Kale and Mushroom Muffins
You’ll Need (Serves 2)
- 120g kale
- 150 chestnut mushrooms, sliced
- 5 tbsp coconut oil
- 3 clove garlic, crushed
- a few sprigs of thyme, leaves picked
- a squeeze of lemon juice
- 1 red onion, diced
- 1-2 tsp red chilli flakes
- 8 eggs
- 2 tbsp coconut milk
- salt and pepper
- extra coconut oil for greasing muffin tray, if not using paper case
- Preheat the oven to 180C/350F fan, and grease a 12 hole muffin tin.
- Heat 1tbsp of the coconut oil in a frying pan and cook the mushrooms on a medium high heat for about 8 minutes until they go golden brown. Lower the heat, add the garlic and thyme and cook for 2 minutes. Add a generous squeeze of lemon juice, toss and remove from the heat as it sizzles, leave to cool in mixing bowl.
- In the same pan, heat the remaining coconut oil and cook the onion and chilli flakes for 4-6 minutes, until softened, leave to cool. In a large pot of boiling water, blanch the kale for 2 minutes and refresh in cold running water. Squeeze out any excess liquid with your hands and roughly chop half the kale, set aside.
- Add the remaining half to a blender, along with the eggs, coconut milk and parsley and blend until it is a smooth green. Mix the liquid with the rest of the ingredients, season generously and divide into 12 muffin tins, use paper cases if you have them as they are easier to take on the move with you.
- Cook for 20-25 minutes or until a skewer comes out clean. Leave to cool for a few minutes in the tin then, run a knife around the edges and turn out to cool on a rack. Delicious warm or cold, keep well in the fridge, and can also be frozen.
(1) USDA (2015) NDL/FNIC food composition database home page. Available at: http://ndb.nal.usda.gov (Accessed: 6 January 2016). (2) Sommerburg, O., Keunen, J. E. E., Bird, A. C. and van Kuijk, F. J. G. M. (1998) ‘Fruits and vegetables that are sources for lutein and zeaxanthin: The macular pigment in human eyes’, British Journal of Ophthalmology, 82(8), pp. 907–910. (3) Murador, D. C., Mercadante, A. Z. and de Rosso, V. V. (2016) ‘Cooking techniques improve the levels of bioactive compounds and antioxidant activity in kale and red cabbage’, Food Chemistry, 196, pp. 1101–1107. (4) Cartea, M. E. and Velasco, P. (2007) ‘Glucosinolates in Brassica foods: Bioavailability in food and significance for human health’, Phytochemistry Reviews, 7. (2), pp. 213–229. (5) Dal Maso, L., Bosetti, C., La Vecchia, C. and Franceschi, S. (2008) ‘Risk factors for thyroid cancer: An epidemiological review focused on nutritional factors’, Cancer Causes & Control, 20. (1), pp. 75–86. (6) Krajcovicová-Kudlácková, M., Bukova, K., Klimes, I. and Seboková, E. (2003) ‘Iodine deficiency in vegetarians and Vegans’, Annals of Nutrition and Metabolism, 47. (5), pp. 183–185. (7) Bath, S. and Dietitian. British Dietetic Association (2014) Food fact sheet. Available at: https://www.bda.uk.com/foodfacts/Iodine.pdf (Accessed: 17 January 2016). (8) Chu, M. and Seltzer, T. F. (2010) ‘Myxedema coma induced by ingestion of raw Bok Choy’, New England Journal of Medicine, 362(20), pp. 1945–1946. (9) Johnson, I. T. (2002) ‘Glucosinolates: Bioavailability and importance to health’, International Journal for Vitamin and Nutrition Research, 72(1), pp. 26–31.
*Interestingly, organic milk has about 40% less iodine than non-organic milk.