Where are you starting from?
The dietary restriction programme is not a weight-reducing approach as such. Its two aims are: health promotion (whether this be prevention of normal / common age-related health problems, or recovery from current ill health); and promotion of life extension. It is clearly quite impossible to guarantee that either of these aims will be achieved, and so anyone who is applying the methods must understand that they alone will able to judge whether or not they are sufficiently impressed by the evidence to become motivated to apply the programme, and ultimately whether they are pleased with the results.

Although the aims are not weight reduction, dietary (calorie) restriction almost always leads to this, and we must be clear that changes in weight are often an important guide to the way you are responding to the programme (and therefore to how efficiently you are applying the methods).

Assuming your age and health status do not bar you from applying the diet, your first step is to establish an important guideline, and this requires that you determine your 'set point' weight level.

How do you find your 'set point'?
If you have remained fairly stable since your 20s or early 30s, note down your average weight during that time. This is your 'set point. If you have steadily gained weight since that period of your life, then note down what your average weight was in your 20s or early 30s. This is your 'set point. If you have experienced a rapid weight gain (or loss) then this should be investigated by a health professional before you adopt any of the methods outlined. There could, for example, be a hormonal or other imbalance which requires attention.

Once you have established your 'set point' weight level you need to keep it in mind as the dietary approach progresses, ensuring that at no time does your weight fall below it by more than 25 per cent. For example, if your 'set point' is 60 kilos (1321b/9.5 stone) you must not let your weight drop below 45 kilos (991b/7 stone). If your 'set point' is 80 kilos (1761b/12.5 stone) your weight should not be allowed to drop below 60 kilos (1321b/9.5 stone). Simple arithmetic, using the 'set point' as your guide, will give you your absolute limit of weight loss below which safety is being risked.

On the other hand, in order to achieve benefits from the diet you should try to ensure that if your 'set point' and your present weight are the same, that after 12 months you have achieved at least a 10 per cent reduction in weight (which is also a 10 per cent reduction from your 'set point'); and if your 'set point' and weight are different (because you have gained weight since your 20s), that within a year you should have achieved at least a 10 per cent reduction in what your weight was at the start of the diet. (This will not, however, be a 10 per cent reduction in weight from your 'set point, which might take much more than a year to reach.)

So if your 'set point' and your weight at the start were the same, at 60 kilos (1321b/9.5 stone) you must try to reach a weight of 54 kilos (1191b/8.5 stone) within a year. If your 'set point' and weight at the start were the same, at 80 kilos (1761b/12.5 stone), you should reach 72 kilos (1581b/11.5 stone) within a year to begin to benefit from dietary restriction. If, however, your 'set point' is 60 kilos (1321b/9.5 stone) and because of weight rise since your 20s your present weight is now 70 kilos (1541b/11 stone), your weight should have reduced to 63 kilos (1391b/10 stone) by the end of the first year. Your 'set point' being 60 kilos determines that for benefits to begin to be gained you need to stabilize your weight loss at under 54 kilos, so this (life extension) target may not be reached for several years. Nevertheless, during this time a host of health benefits should start to be noticed.

Remember that the 'set point never changes, since it is based on what your weight was in the past (unless you are still in your 20s in which case it is your present weight, as long as this is stable). If you have not lost either 10 per cent of your 'set point' weight after 12 months, or 10 per cent of your total weight after 12 months (if your 'set point' and starting weight were different) you should reexamine how efficiently you are applying the rules of dietary restriction.

Your 'set point' is your baseline
Your 'set point' weight is a key number. It gives you a marker from which you can assess whether you are achieving successful modification of metabolic rate through calorie restriction, by keeping a check on weight loss, and it also allows you to monitor the speed with which this is happening. It is important that any weight loss is not fast. The aim is a slow reduction of anything from 1-41b a month (depending on how much body fat you are starting with) from your 'set point' weight (or starting point weight, if these two figures are different).

To recap, the safe long-term (it could take several years) target you are aiming to reach is a reduction to not less than 10 per cent and not more than 25 per cent below your 'set point' weight. At that time the full benefits of dietary restriction will be operating (reduced free radical activity, more thrifty energy processes etc.). Never allow your weight to drop below 75 per cent of your 'set point' weight.

How quickly?
The time it takes you to reach your target weight should be anything from 12 months to several years. The older you are when you start the programme the longer you should take to achieve this target weight. One of the joys of this approach following a 1,800 to 2,000 calorie per day diet) is that it is highly unlikely that you will ever drop below 75 per cent of your 'set point' weight. By the time you have reached the safe weight level your metabolic machinery should have adjusted to the reduced energy intake, becoming ever more efficient, and maintaining you at this optimum weight indefinitely.

Daily protein and fat requirement
Apart from your 'set point' weight you also need to record your present weight, since you will need it as a guide to your ideal protein and fat intake. If you have remained stable in weight since your 20s, then your 'set point' weight will also be your present weight. If you have altered in weight since your 20s you should now record your present weight. You use this figure to calculate how much protein and how much fat you should consume daily as part of your restriction diet. The guidelines for this are: 0.8 to 1.0 grams of protein daily for each kilo of your present body weight, and 0.4 to 0.6 grams of fat daily for each kilo of present body weight.

Protein calculation
It is now time for some simple arithmetic. Multiply your present weight in kilos by 0.8 and by 1.0. Let's say you weigh 60 kilograms:

60 x 0.8 = 48
60 x 1.0 = 60

You need to eat not less than 48 and not more than 60 grams of protein daily, until you start to lose weight, at which time you will need to recalculate your protein intake based on your new body weight. You should do this about once a month, taking your new body weight as your main number and multiplying it by 0.8 and 1.0 for your new daily protein requirement.

Note: If your body weight is different from the example given above (of someone weighing 60 kilos) you need to use your weight in this calculation.

Fat calculation
To discover your fat requirement take your present body weight and multiply this by 0.4 and 0.6. If your present body weight is 60 kilograms:

60 x 0.4 = 24
60 x 0.6 = 36

You need to eat not less than 24 and not more than 36 grams of fat daily, until you start to lose weight, at which time you will need to recalculate your fat intake based on your new body weight. You should do this about once a month (until you reach your target weight at which time it will stabilize at that level), taking your new body weight in kilos as your main number and multiplying it by 0.4 and 0.6 for your new daily fat requirement.

Note: If your body weight is different from the example given above (of someone weighing 60 kilos) you need to use your weight in this calculation.

Guidelines will be given later in this chapter on how this protein and fat content of your diet might be made up.

Reminder: It is essential that you readjust your protein and fat intake as the weight loss progresses, to match your present body weight at all times. Each time fat and protein levels are reduced to match your reduced weight it is also necessary that you then increase your intake of calories from other sources (complex carbohydrates such as whole grains, fruit and vegetables, for example) so that the 1,800 to 2,000 daily intake of calories is maintained. Help is given in the next chapter on how you might best work this out.

1,800 or 2,000 daily?
If you are over 50 years of age it is suggested that you do not allow weight loss to occur too fast (especially if you are overweight) and that you therefore stick to 2,000 calories per day. Younger people (20 to 50) can usually afford to lose weight a little faster and can choose between either 1,800 or 2,000 calories a day. This is not a crash diet. It's aims are not to produce weight loss as an end in itself but quite simply to improve health and to encourage life extension.

An almost automatic by-product of the method will be a loss in weight, which is used as a guide to how efficiently your body is adjusting to caloric restriction, the one and only proven method for achieving life extension to date, with a host of positive health benefits added as a bonus.

Calculating calories
We all know the expression (taken from the title of a famous diet book) that calories 'don't count'. This expression was used to point to the fact that people who tried to slim using calories as their sole guide, and who applied diets of 1,00.0 calories (often less) for lengthy periods, frequently failed to achieve their objectives. This was often because dietary change was too quick ('crash' diets) and restrictions too great. It also had much to do with the thoroughly unbalanced way the limited calorie intake was made up.

The life extension diet does not try to aim at weight loss. It is essentially a slow process and it does not reduce intake of food to ridiculous and unsustainable levels. When weight reduction is too fast, compensating mechanisms are triggered in the body which try desperately to retain weight levels. Life extension diets, because they use only a moderate reduction in food intake, and because they insist on adequate protein, fat and all other nutrients apart from calories, and because the quality of the food eaten is seen to be at least as important as how much is eaten, do not produce this type of defensive reaction and are sustainable for years (indeed, for a lifetime - a long one it is hoped).

Once established, the natural life extension diet is easily maintained, does not produce the sort of social difficulties which extremely limited diets do, and allows a normal life to continue with no feeling of deprivation. The need to count calories in this instance is therefore not the same as in strict crash diets, but rather as a means of giving a pattern to eating which is easy to follow. The way this is done is by means of what has become known as an 'exchange diet' about which I have more to say below.