Scientists have evidence that Popeye was right: Spinach makes you stronger. But it’s the high nitrate content in the leafy greens — not the iron — that creates the effect. Building on a growing body of work that suggests dietary nitrate improves muscle performance in many elite athletes, researchers at Washington University School of Medicine in St. Louis found that drinking concentrated beet juice — also high in nitrates — increases muscle power in patients with heart failure.“It’s a small study, but we see robust changes in muscle power about two hours after patients drink the beet juice,” said senior author Linda R. Peterson, MD, associate professor of medicine. “A lot of the activities of daily living are power-based — getting out of a chair, lifting groceries, climbing stairs. And they have a major impact on quality of life. We want to help make people more powerful because power is such an important predictor of how well people do, whether they have heart failure, cancer or other conditions. In general, physically more powerful people live longer.”