The spinach-eating cartoon character Popeye has much to teach us, new research from the Swedish medical university Karolinska Institutet shows. The muscles'cellular power plants - the mitochondria - are boosted by nitrate, a substance found in abundance in vegetables such as lettuce, spinach and beetroot. "The mitochondria play a key role in cellular metabolism,"says Professor Eddie Weitzberg, who is heading the study with Professor Jon Lundberg. "Improved mitochondrial function probably has many positive effects on the body, and could explain some of the health benefits of vegetables.