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.
Glycemic index
63
Medium
Boiled. Roasting it until it caramelises pushes it higher, and it varies a lot by variety.
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. Let it cool afterwards and eat it cold or a day later, and you get resistant starch with it.
Combine with
Olive oil or avocado oil
The orange colour is provitamin A and it only dissolves in fat. Without fat you are mostly eating the starch.
What it does
Let cooked starch cool and part of it crystallises into resistant starch: it reaches your large intestine undigested and the bacteria there turn it into butyrate, the fuel your colon wall runs on. In a randomised trial in 42 older and 42 mid-age adults, butyrate in the stool rose in the older group, and Bifidobacteria increased in both groups.
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.