By Harold McGee
There’s a useful guideline for estimating the relative healthfulness of vegetables and fruits: the deeper its color, the more healthful the food is likely to be. The more light a leaf gets, the more pigments and antioxidants it needs to handle the energy input, and so the darker the coloration of the leaf. For example, the light-colored inner leaves of lettuce and cabbage varieties that form tight heads contain a fraction of the carotene found in the darker outer leaves and in the leaves of more open varieties. Similarly, the dark leaves of open romaine lettuce contain nearly 10 times the eye-protecting lutein and zeaxanthin of the pale, tight heads of iceberg lettuce. Other deeply colored fruits and vegetables also contain more beneficial carotenoids and phenolic compounds than their pale counterparts. Their skins are especially rich sources. Among the fruits highest in antioxidant content are cherries, red grapes, blueberries, and strawberries; among vegetables, garlic, red and yellow onions, asparagus, green beans, and beets.