Romaine
The lettuce with a firm heart and more taste than a butterhead. A bowl of leaves you build a meal around.
Glycemic index
None. There are hardly any carbohydrates in this, and the index measures what carbohydrates do to your blood sugar.
How to use it
Raw as the base of a salad, or the hearts halved over the grill. The stiff rib holds a dressing where soft lettuce collapses.
The best version
A head with a closed heart and firm, snapping ribs. Loose leaves in a bag have already been washed, and that costs shelf life and taste.
How to prepare it
Wash leaf by leaf and spin dry. Cutting with a knife browns the edges faster than tearing by hand.
Combine with
A dressing with oil
Lettuce without fat gives up almost none of its pigments. With fat alongside, lutein from a salad reached the blood at five times the level.
What it does
Leafy greens supply nitrate, and nitrate becomes nitric oxide in your body, which relaxes your blood vessels. That mechanism was measured with beetroot juice: seven trials, 218 people with high blood pressure, systolic pressure down by 4.95 mmHg.
Watch out
Romaine itself has not been tested that way. What you certainly get is volume and fibre; the rest is the mechanism and not this lettuce.