Free radicals are chemicals that possess unpaired electrons. This makes them chemically very reactive. Free radicals can react with other chemicals, and in the process electrons are transferred to the radical, causing the other reactants to become destabilised to a radical. This process then continues in a free radical chain reaction. If such a chain reaction occurs in human tissue, significant damage can be done, particularly to lipid soluble cell membranes. Such free radical damage leads to oxidative stress, and this is now thought to be a major contributory factor in the development of disease. Plants are an excellent source of antioxidants, because they synthesise phytochemical antioxidants for their own protection. When we eat plants we absorb the antioxidants, and they confer health benefits. It is often assumed that antioxidants must be absorbed to the circulation and accumulate in our tissues in order to have health benefits. However, antioxidants may offer health benefits even if they are not absorbed.
Recent evidence suggests that antioxidants may confer health benefits through their effects on food. Cooking foods exposes sensitive chemicals such as polyunsaturated fatty acids to reactions with other molecules including oxygen. This can damage the molecules and form a range of toxins including lipid peroxides. When ingested lipid peroxides may cause oxidative stress and lead to disease. Cooking foods with antioxidants may limit the damage to polyunsaturated fatty acids because the antioxidants are able to protect the sensitive double bonds on the fats through increased reducing power that inhibits or reverses oxidative reactions. In this regard spices, red wine, fruit and vegetables can all provide protection to fats during cooking. Recent evidence for example suggests that some of the protective effects of red wine may come from this ability to prevent lipid peroxidation before the food components are absorbed. Adding herbs and spices to food may be beneficial to the health irrespective of the subsequent absorption rates.