Radicchio is a slightly bitter leafy vegetable, an Italian chicory. In the United States, the better-known variety is the Verona, resembling a tiny head of purple cabbage, but farmers’ markets and greengrocers often carry the Chioggia variety that looks like lettuce, and the Treviso that with its long, scarlet leaves looks something like a reddish version of Belgian endive. In the late summer the root of the Treviso variety sprouts single leaves. In Italy and in Italian markets in the United States the late-season raddichios are sold as tardivo.
Nutritionally, radicchio is more important for what it does than for what it contains. Radicchio and other chicories contain a special class of carbohydrates known as fructans, a group containing inulin (not to be confused with insulin) and oligofructoses. These carbohydrates feed the symbiotic bacteria living in the intestine rather than the human body itself. They allow the healthy bacteria in the colon to produce short chain fatty acids that help prevent colon cancer, but they do not serve as a food source of pathogenic bacteria.
The bacterial fermentation of fructans in the intestine changes its chemistry so that the human body absorbs calcium and magnesium much more readily from other foods, so much so that consuming radicchio and similar vegetables demonstrably builds stronger bones. Moreover, even cooked radicchio retains its naturally high concentration of vitamins and antioxidants.
Except for tardivo, the older the radicchio, the more bitter its taste. You can keep radicchio in the vegetable crisper of your refrigerator for up to a week. To prevent spoilage, don’t wash radicchio until just before use. If you slice up radicchio and find it too bitter to your taste for use in a salad, don’t throw it away. Radicchio and other chicories make an interesting contrast in bland dishes such as white beans or risotto. Or use radicchio as one of the toppings for your next pizza. It especially complements the flavors of Gorgonzola cheese.