Research on eggplant has focused on an anthocyanin flavonoid found in eggplant skin called nasunin. A potent antioxidant and free-radical scavenger, nasunin has been shown to protect cell membranes from damage. In animal studies, nasunin has been found to protect the lipids (fats) in brain cell membranes. Cell membranes are almost entirely composed of lipids and are responsible for protecting the cell from free radicals, letting nutrients in and wastes out, and receiving instructions from messenger molecules that tell the cell which activities it should perform. Nasunin is not only a potent free-radical scavenger, but it also helps move excess iron out of the body. Although iron is an essential nutrient and is necessary for oxygen transport, normal immune function, and collagen synthesis, too much iron is not a good thing. Excess iron increases free-radical production and is associated with an increased risk of heart disease and cancer. Menstruating women, who lose iron every month in their menstrual flow, are unlikely to be at risk, but in postmenopausal women and men, iron, which is not easily excreted, can accumulate. By helping to bind excess iron, nasunin lessens free-radical formation with numerous beneficial results, including protecting blood cholesterol (which is also a type of lipid or fat) from becoming a highly reactive toxic form; preventing cellular damage that can promote cancer; and lessening free radical damage in joints, which is a primary factor in arthritis.
Eggplant may also help to lower cholesterol levels. When rabbits with high cholesterol were given eggplant juice, their blood cholesterol, the cholesterol in their artery walls, and the cholesterol in their aortas (the aorta is the artery that returns blood to the heart) was significantly reduced, while the walls of their blood vessels.