Sweet potato
Starch with colour in it. That colour is provitamin A, and in children who were short of it that has simply been measured.
How to use it
As the main source of starch on your plate, in place of white potato or rice. With fat alongside, because the pigment only dissolves in fat.
The best version
The orange kind, and the deeper the orange the more beta-carotene. The white and purple ones are different products with different contents.
How to prepare it
Boiling and mashing gives you the most of the pigment. Roasting makes it sweeter because the starch breaks down, which tastes better and reaches your blood faster.
What it does
In South African schoolchildren it was measured directly. Ninety children ate 125 grams of boiled, mashed orange-fleshed sweet potato on 53 school days, and ninety ate the same amount of the white kind, which has no beta-carotene. Vitamin A stores in the liver improved in the orange group and not in the white one.
Watch out
It is still a starch. Roasted until it caramelises it reaches your blood quickly, and then the difference from an ordinary potato is smaller than the colour suggests.