Atoms 'hold' on to each other, or link, just as hydrogen and oxygen atoms combine to form water, for example. When water is formed, two hydrogen atoms are joined electrically to one oxygen atom, giving us the formula H2O for the fairly stable water molecule. When two hydrogen atoms link, however, to two oxygen atoms, an unstable molecule of H2O2 - hydrogen peroxide - is formed, and everyone knows what bleach can do to hair when its rampant free radicals touch it.

The processes of linking and breaking of molecules are constant features of all of life's activities, with enzymes acting as catalysts to allow the joining and unjoining of atoms and molecules to occur smoothly. When something burns or rusts it is because of the activity of unlinked atoms or molecules which have a tendency to latch onto other molecules, damaging in the process by removing one of their electrons. This is what happens when metal rusts, rubber perishes, a sliced apple turns brown when exposed to air, fats go rancid or hair is bleached . . . and so on.

Protection from antioxidants
We live in an oxygen-rich environment, in which there are abundant opportunities for exposure to oxidative stress, and this is particularly true of body cells where oxygen is part of the energy production cycle. Damage to cell membranes (or their fat content) and other key parts of the cell, including the genetic material (DNA, RNA) itself is possible, unless a variety of valuable protective molecules (such as enzymes, and vitamins A, C and E) act to contain and control free radicals by use of their antioxidant abilities. This is why lemon juice (vitamin C) squeezed onto a sliced apple prevents browning from taking and why vitamin E prevents fats and oils from oxidizing. Some people are better endowed with antioxidant protectors than others (a lot to do with their diets) and some people produce free radicals far more freely than do others.

How much antioxidant (protective) potential is present and how great a need there is for it, are the key elements which decide how much free radical damage will result, and the extent of disease and dysfunction that will follow. Many major chronic diseases, often associated with ageing, are now thought to be largely the result of free radical activity, including arterial disease (atherosclerosis) and cancer.

Are you a 'burner' or are you 'thrifty'?
Weindruch and Walford have dubbed some people (and animals) 'burners' and others 'thrifty' since they believe, and give ample evidence to support the idea, that the efficiency with which mitochondria produce the substance ATP (adenosine triphosphate, from which the body derives its energy) varies greatly from person to person, and from animal to animal. Although the degree of efficiency is probably genetically determined, it is seen to improve somewhat with dietary restriction (and with antioxidant nutrition).

Those people (and animals) who are somewhat 'sloppy' and inefficient in their energy production activity, and who release an undue amount of heat and possibly free radicals in the process, are termed 'burners'. While those who efficiently transfer raw materials (food) into ATP, with little wastage in terms of heat or free radical activity, are called 'thrifty'.

It is important to remember that the more efficient the energy production, and the fewer free radicals emerging from the process, the greater the tendency for a longer life span. And since dietary restriction seems to encourage a 'thriftier' level of energy production, there seems little doubt that life extension is at least partly the result of improved energy production efficiency and lower free radical activity.