structural:summarization, linguistic:paraphrasing
Phytochemicals

Kale is a source of the carotenoids, lutein and zeaxanthin. As with broccoli and other cruciferous vegetables, kale contains glucosinolate compounds, such as glucoraphanin, which contributes to the formation of sulforaphane, a compound under preliminary research for its potential to affect human health beneficially.

Boiling kale decreases the level of glucosinate compounds, whereas steaming, microwaving, or stir frying does not cause significant loss. Kale is high in oxalic acid, the levels of which can be reduced by cooking.

Kale contains high levels of polyphenols, such as ferulic acid, with levels varying due to environmental and genetic factors.