Nobody welcomes the physical deterioration that accompanies the later stages of ageing - and finding a way to retard or prevent this process has long been a dream of medicine. Certainly a healthy lifestyle incorporating aerobic and load-bearing exercises and appropriate diet can help to counteract the inevitable physical deterioration. Dr William Reville writes
That apart, little progress has been made otherwise in slowing down or halting this basic background deterioration. However, a promising approach has now been identified and is described by Mark Lane, Donald Ingram and Mark Roth, Scientific American (August 2002).
The new approach is based on a fascinating observation that scientists have known about for 60 years. It was observed that laboratory rats fed a low-calorie (LC) diet not only lived longer on average than free-feeding rats, but were significantly less prone to develop conditions that become increasingly common in old age. Perhaps the most exciting observation was that some of the rats on LC diets lived longer than the oldest rats on the free-feeding diet.
A free-feeding rat has a maximum life span of slightly more than three years. An LC diet can increase this by 50 percent. In order to achieve this the daily calorie intake must be reduced by about 30 percent. The LC effect has been noted not only in rats, but in many other species including yeast, worms, fish, spiders, mice and hamsters.
To date the LC effect has mainly been investigated in short-lived species that are genetically distant from humans. However, recent studies on monkeys indicate that humans would react to an LC diet in much the same way as all the other species studied.
The detailed effects of LC diets compared to free-feeding controls that have been catalogued in rodents and monkeys include the following: lowered body temperature; later sexual maturation; lower weight; less abdominal fat; lower fasting levels of insulin and glucose; lower cholesterol levels; later onset of age-related diseases (including cancer); longer average life span; longer maximum life span.
SO if we want to live longer and healthier why don't we all go on LC diets? The problem is that such a diet would represent quite a harsh regime. A daily calorie intake reduction of 30 percent would make you feel hungry and cold and with little energy for exercise. Very few people would have the will power to endure such conditions for long. The ideal solution would be to trick the body into thinking it is on an LC diet while maintaining normal levels of food intake. Finding ways to do this is now the focus of much research.
Most of the energy (calories) we derive from a normal diet comes from glucose. All cells in our bodies chemically break down glucose in a long sequence of steps (metabolism) and tap off chemical energy in the form of a chemical called ATP.
Unfortunately, this process generates byproduct chemicals called free radicals. Free radicals cause damage in the cell and their action can be likened to a scissors randomly snipping at its surroundings. The cell has mechanisms to repair this damage, but over time the effects gradually accumulate. This is one credible theory of why cells deteriorate during ageing - the gradual failure of cell maintenance to keep pace with this attrition.
The authors accept this ageing hypothesis and use it to explain the LC diet effect. Considerably less glucose is metabolised by someone on an LC diet and correspondingly, considerably fewer free radicals are generated. The cell is spared a significant amount of damage. They reasoned that the same effect could be produced by slowing down the rate of metabolism of the glucose content of a normal diet.
Lane and his co-workers investigated the effect of adding 2-deoxy-glucose (2DG) to the diet of free-feeding laboratory rats. 2DG is a close chemical relative of glucose and is taken up and metabolised by the cells. Its net effect is to slow down the metabolism of ordinary glucose so that less ATP is made and fewer free radicals are produced - the same results as produced by an LC diet. Studies have also shown that 2DG also mimics other effects of an LC diet including lower body temperature, lower weight and later onset of age-related diseases.
Unfortunately it has also been noted that higher levels of 2DG administration, or prolonged administration at lower doses is toxic to rats. Therefore, 2DG could never be approved for human use. However, there is good reason to suppose a safe alternative chemical will become available and several options are presently being tested.
We are genetically programmed to have a maximum human life span of about 110 years. The average life span at present is about 75 years. This may slowly inch upwards in future, but I feel it will be a long time before the average approaches the maximum and much longer again before humans will be able to set a higher maximum.
In the meantime, eat moderately across the four food groups, take regular aerobic exercise. Don't smoke, drink alcohol in moderation, help others when you can, relax, and develop a philosophy of life. And don't spend too much time along the way plotting and planning to live forever.
William Reville is Associate Professor of Biochemistry and Director of Microscopy at UCC