What is it?
A leafy green veg from the same family (Brassica oleracea) as cabbage and broccoli.
The health claims?
- Kale is a ‘super’ green that’s packed with vitamins (K, A and C), minerals (iron and manganese), antioxidants and fibre
- It’s the most nutritious green vegetable
- It can help prevent cancer
The scientific facts?
- When eaten raw, kale is indeed a nutritional powerhouse. It’s high in vitamin K (for good blood clotting), A and C (1 cup of kale boasts more vitamin C than an orange and 10 times more than a cup of spinach), and a good source of manganese (for connective tissue formation), copper and calcium.
- It’s not as high in iron as commonly believed, providing 1.5mg of iron per 100g bag of kale; spinach is a better source of iron at 2.7mg per 100g.
- It’s high in antioxidants like beta carotene, vitamin C, flavonoids and polyphenols, but as this study demonstrates cooking kale dramatically reduces its nutritional value.
- According to the US’s Aggregate Nutrient Density Index (a scoring system for the nutritional density of foods) kale is the most nutrient dense food, with a score of 1000 out of 1000 – strong evidence that it is deserving of its ‘most nutritious vegetable’ title. FYI: cola comes out as the least nutrient dense food with a score of 0.6!
- Health claims that kale can help prevent (not cure) cancer are scientifically founded. Studies, like this one have found a positive correlation between eating cruciferous veg like kale, broccoli and cabbage and reduced cancer risk. But the reason why is still unclear.
Nutritional facts – Spinach versus kale
Spinach is kale’s better known rival in the superfood stakes. Here’s how 100g of each compares:
- Kcals (per 100g): Kale 49 v Spinach 23
- Vitamins: Kale is higher in vitamin A, C, K and all B vitamins
- Minerals: Kale is lower in iron, potassium and magnesium than spinach, but higher in calcium.
- Fibre: Spinach is slightly higher in fibre than kale.
- Antioxidants: Both are high in carotenoids, flavonoids and vitamin C, but kale has more than spinach.
Winner: Kale – it’s higher in almost all of the nutrients that spinach is renowned for.
Worth the hype?
Yes – when eaten raw (that means those kale chips that have been baked are not worth the money or hype). An added bonus is that kale is cheaper to buy than spinach and other leafy veg, at around £1 per 200g bag.
The biggest downside of kale, however, is that it doesn’t taste all that great raw, and can cause trapped wind and constipation when introduced into the diet because it’s high in insoluble fibre. But it’s worth persevering as this kind of fibre is known to help reduce the risk of bowel conditions including cancer.