A powerhouse green leafy vegetable with some of the most concentrated nutrients of any food, kale (Brassica oleracea acephala) is the closest of the Brassica family to the original wild cabbage. Until the end of the Middle Ages, kale was the most widely eaten green vegetable in Europe. There’s evidence that both curly and flat leaf varieties were eaten as far back as the 4th century BCE in Greece. The Brassica family is a large family that includes broccoli, Brussels sprouts, cabbage, cauliflower, collards, kohlrabi, mustard, turnips and rocket, among others.
Nutrients in kale
One cup of kale contains about 40 calories, low oxalates (so mineral absorption is improved) and significantly more nutrients overall than spinach. It contains minerals such as copper, potassium, magnesium, manganese, iron and phosphorus, along with almost 3g of protein, vitamins A, C, E and K, B vitamins and a range of the antioxidant and anti-inflammatory flavonoids.
A delicious food that is also a medicine
Minerals
The high levels of calcium and magnesium in kale support strong bones, skin and hair, being higher per calorie in calcium than cow’s milk. Magnesium assists in calcium metabolism in the bone, thus being protective against both osteoporosis and osteoarthritis.
Vitamins
High in provitamin A and the related carotenoids, lutein and zeaxanthin, kale benefits your skin and is protective against the eyesight condition called macular degeneration. Vitamin A also “moisturises” both the skin and the lung membranes.
Vitamin K is crucial for strong bones as well as correct blood clotting. Vitamin K modifies bone matrix proteins, improves calcium absorption and reduces calcium excretion — and kale has substantial levels of this vitamin.
Antioxidant & anti-inflammatory
Kale contains:
- Sulphoraphane: a major antioxidant with anticancer and antimicrobial properties that stimulates natural detoxifying enzymes in the liver.
- Indole-3-carbinol: this aids in DNA repair and improves liver metabolism of oestrogen, helping protect against the cancers such as breast and prostate cancer.
- Omega-3 fatty acids: a cup of kale per day can give you 10 per cent of the recommended daily allowance. The omega-3 fatty acids are major regulators of inflammation.
- Flavonoids: quercetin and kaempferol are important anti-inflammatory compounds.
Let’s not forget the high fibre
Kale has extraordinary levels of fibre for a green leafy vegetable, so is excellent for digestion and bowel function, along with improved management of blood sugar and cholesterol. The fibre also helps you to feel full after eating, so reducing overeating and proving useful for weight management.
Systems thinking
Respiratory system
Eating kale (a bitter food) regularly eases lung congestion and reduces asthma risk. Research shows that bitter foods reduce asthma attacks. There are bitter receptors in the tissue lining the lungs and the bitter taste triggers a relaxant effect in the lungs (as well as improving digestion).
Cardiovascular system
With its high levels of potassium, kale is protective of the heart.
Endocrine system
Research has shown that abnormal blood sugar symptoms are improved by eating a high-fibre diet. Fibre in food stabilises blood sugar, blood lipids and insulin levels. Kale also contains alpha-lipoic acid, which improves liver function, stabilises blood sugar and increases the sensitivity of insulin.
Immune system
The high chlorophyll component of kale is effective in blocking the carcinogenic effects of the heterocyclic amines produced when grilling, barbecuing or frying foods at high temperatures.
Too much of a good thing?
Raw kale in high doses can be goitrogenic — as are all the brassicas. The glucosinolates produce a compound called goitrin, which can interfere with thyroid hormone synthesis (cigarette smoking can do the same). It’s a dose issue, however, and normal eating (several serves a week) of this amazing vegetable will rarely cause problems.
“Tricks” to reduce the impact of goitrogens
- Cooking breaks down goitrogens and significantly reduces the levels.
- Seaweed or iodine-rich foods, or supplementing with iodine, reduces the problem.
- High selenium foods such as Brazil nuts will normalise iodine (and therefore thyroid hormone) levels.
- Eating a wide variety of vegetables without goitrogens, such as celery, parsley, zucchini, carrots etc is a good nutritional policy as a diet like this supplies the wide variety of nutrients essential for health.
Indigestible raffinose
Brassica vegetables are high in an insoluble carbohydrate that is difficult to digest: raffinose. This can cause bloating and wind and problems in those with irritable bowel conditions. On the positive side, raffinose encourages the growth of beneficial bacteria in the gut. Cooking kale improves its digestibility as it breaks down the tough fibre components. Adding spices when you cook it, such as black pepper, cumin, fennel or fresh ginger root, also makes it more digestible. If you want to eat kale raw, “massage” it. Massaging the leaves helps break down the tough fibres and largely removes the bitterness.
Note: Avoid kale if taking the blood-thinning drug warfarin or other blood-thinning medication.
