Leafy vegetables are chock-full of nitrate — a molecule that seems to boost the efficiency of energy-producing organelles called mitochondria in muscle cells.

Filip Larsen, Eddie Weitzberg and their group at the Karolinska Institute in Stockholm gave 14 volunteers either doses of nitrate similar to those found in certain foods or a placebo. Mitochondria collected from the muscle cells of those who had been taking nitrate for three days made 19% more energy-dense ATP molecules per oxygen molecule consumed than did those on the placebo.

Mitochondria must maintain an electrochemical gradient across their inner membrane to produce ATP. Levels of a protein that saps these organelles' conductivity were reduced in people taking nitrate, suggesting that their muscle cells were producing energy more economically.

Cell Metab. 13, 149–159 (2011)