The possibilities are many. Dietary restriction could reduce the metabolic rate, slowing down the function of energy consumption, i.e we could 'burn' less. Or it could be that the efficiency with which the organism handles energy improves when dietary restriction is operating. It might also be that there are fewer free radicals generated when dietary restriction is applied, since these rogue molecules are a by-product (amongst other things) of energy production processes involving oxygen; or it might be that the toxic by-products of oxygen are better dealt with during dietary restriction. Or perhaps all of these things happen to the benefit of the organism when calorie (energy) intake is reduced.

How much energy do you use?
A distinction is made between energy production in the mitochondria (a cell's energy source) which takes place in muscle and that which takes place anywhere else in the body (non muscle). From the aging viewpoint it is known that total energy consumption, as well as muscular energy consumption declines with age. Muscular energy use accounts for around a third of the energy used when we are at rest, and upwards of 90 per cent of energy used during heavy activity. The overall decline seen when we (or animals) age is therefore probably because muscle mass also declines with age, by around 3.5 per cent every 10 years. Quite simply less muscle uses less energy. With advanced age, however, energy consumption by non-muscle tissue (organs, brain etc.) increases, and this is thought to relate to the development of diseases affecting these areas (cardiovascular problems, cancers etc.).

At age 30 our non-muscle energy consumption amounts to around 38 per cent of our total energy use on average, but by the age of 80 this will have risen to over 50 per cent of energy use. Dr Totter, whose evolutionary ideas have been already referred to, believes that energy consumption by non-muscular tissues (in reproductive processes as well as organ function) are potentially harmful because this is, as he puts it: 'The main sources of oxygen (free) radicals that maybe the direct cause of aging.' Most muscular energy consumption is not regarded by Totter as producing free radical activity, and Weindruch and Walford remind us that evidence to date in longevity research has shown that active exercise has little or no effect on life span, which supports the idea that muscle metabolism is not much involved in the ageing process.

They have evaluated the research to date on the vital state of mitochondria (the energy producing unit of the cell) and conclude that it may not be possible to point to them as having a direct relation to the aging process, but that since they are continually being replaced as they become inefficient through wear and tear, this 'provides an endless source of active oxygen which can attack other critical parts of the cell'

Free radicals and the ageing process
In Chapter 8 I give a detailed account of the connection between free radicals and ageing, the so-called 'rusting' theory. Free radicals are certainly part of the energy production scene and need to be understood in this context as well as the more general setting of their influence on the rest of the body.

All atoms carry electrical entities, protons (positively charged) and electrons (negatively charged), and these are in orbit around the nucleus of the cell. When atoms combine to form molecules it is through a balanced linking of these various electrical potentials, leaving a neutral (electrically speaking) end product. However, in some instances an unpaired electron remains spinning in orbit around the atom or molecule, ready to latch on to any passing atom or molecule to which it can attach itself. When this happens it will break existing bonds, destroying the electrical links of previously balanced molecules or atoms, a process which happens when oils or fats go rancid or oxidize in the presence of the oxygen in air. Energy is released in the process, and a chain reaction of more combustion or damage continues as the newly formed, damaged, molecules continue the process of grabbing electrons wherever they can. So a free radical is an unbalanced (electrochemically speaking) unpaired atom, or particle of a molecule (itself a combination of atoms), which is desperately seeking an electron with which it can link via its 'free' attachment site.