The orthodox Golden Rule for treating overweight is: calories in minus calories out equals weight change. As you will see later, although this hypothesis looks plausible on the surface and has what looks like umpteen good, solid, rigorous, clinical studies appearing to support it, it is actually quite wrong.

However, if we assume it is correct, that brings up the first big problem: How do we answer the apparently simple question: How many calories are there in an item of food?

Despite supermarkets' desire for uniformity, natural food products can vary widely from item to item. An early season fruit, for example, may be much lower in sugar than one from the peak of the season; a green banana is mostly starch, while an overripe one is mostly sugar.

And that is only the first problem. The second is even harder to answer: How much energy do you use when you do something? If you walk a mile you will use less energy than someone else who walks the same distance, but weighs more. If you do it quicker your energy usage will differ from someone doing it slowly.

Studies have shown that when people change to a low-fat diet in a metabolic ward experiment they lose some weight. However, a few weeks later, when these people have returned home, the regulatory systems in their bodies ensures that the weight they lost was replaced. Therefore, it doesn't work. The problem with this approach is that you cannot know how much energy to take in. Neither can you know how much you are using.

When is a calorie not a calorie?

The second Golden Rule of orthodoxy is: 'A calorie is a calorie is a calorie' ? no matter where it comes from. This means that if you eat X number of calories more than you use up, you will put on Y amount of weight, wherever those calories come from. However, as has been demonstrated over and over again from many studies looking at diets with equal calorie content, but different constituents, this is far from true. Dieters on fat-based diets consistently lost much more weight than dieters on carb-based diets, even though both diets had exactly the same number of calories.

Therefore, 'a calorie is a calorie is a calorie' is not so meaningful after all: a carbohydrate calorie is obviously much more fattening than a fat calorie. So obviously some calories don't count as much as others.

There is an emerging scientific consensus that weight control is a highly complex topic and the old ideas that overweight people are lazy gluttons are now realised to be as absurd and insulting as the overweight have always thought they were.

So what went wrong?[1]

With all the evidence that it is carbs and not fats that are the cause of obesity, why is it that those in nutritional authority can't see it? The answer seems to lie in their implicit belief in the First Law of Thermodynamics which states that energy cannot be created or destroyed, merely changed.

Around the end of the nineteenth century, doctors devised a simple concept based on the First Law of Thermodynamics. They likened the body to a tank, into one end of which energy is poured in the form of food. This, they said, was then either used up or stored. If you used up more than you poured in, you got thinner and if you poured in more than you used, you got fatter. The theory was easy to understand, made sense, obeyed the laws of physics, and for a while it seemed satisfactory. Dieticians could now say, apparently with scientific backing, that fat people must either be eating too much or working too little.

By the start of the 1914-18 war, however, doubts were creeping in. For instance, diabetes is a defect of carbohydrate metabolism and the treatment for diabetics at that time involved completely depriving them of carbohydrate. In this case, scientists found that the energy input/energy output sums simply did not add up.

By the early 1920s, interest in the theory was renewed. It was found to be impossible to measure the total amount of water in a person at any one time. Therefore, water retention or loss was said to account for any discrepancy in the balance between energy input/output and excess weight. It was decades before this convenient theory was disproved.

In the 1950s, isotope techniques were developed which allowed more accurate measurement of body fat turnover. In addition, it was demonstrated that different foods could alter the amounts of body fat; and that body fat could also be affected by certain responsive glands - the adrenal, thyroid and pituitary glands - even when energy intake was constant.

The flaws exposed

The fact that high-energy diets are more effective for reducing weight has proved very difficult for dieticians and doctors to accept, because of what looks like a challenge to the laws of thermodynamics. But there are flaws in this theory. To grasp them, we need to go over some basic facts.

The calorie is a unit of heat. The way the energy content of a food is determined is by burning it in a device called a 'bomb calorimeter' and measuring the amount of heat it gives off.

One gram of carbohydrate, burnt in this way gives an energy value of 4.2 calories, or more correctly kilocalories (kcals). A gram of protein gives 5.25 kcals. This time, however, one calorie is deducted because a gram of protein does not oxidise readily, it gives rise to urea and other products which must be subtracted. That gives a final figure for protein of 4.25 kcals. Burning a gram of fat in the bomb calorimeter gives 9.2 kcals.

These figures are then rounded to the nearest whole number - 4, 4 and 9 respectively - and are used in calorie charts to indicate the energy values of foodstuffs and, thus, to allow dieters to measure their food intake.

But there are two basic flaws in using these figures to determine the amounts of food we should eat:

1. The more obvious flaw in the argument is that our bodies do not burn foods in the same way that they are burned in a bomb calorimeter. If they did, we would glow in the dark. Our digestive process is quite inefficient. The chemical process whereby blood sugar is oxidised to provide energy produces carbon dioxide. About half is exhaled as carbon dioxide, the other half is excreted in sweat, urine and faeces as energy-containing molecules, the energy values of which must be deducted from the original food intake. All of these vary. For example, eating a lot of fat forms ketones, which can be found in urine. The value of a gram of ketones derived from fat is roughly four calories. So, in this case, nearly half the energy from the fat is lost.

2. The second and more important flaw in the argument is that the body does not use all its food to provide energy. The primary function of dietary proteins, for example, is body cell manufacture and repair: making skin, blood, hair and finger- and toe-nails, etc. The amount of protein needed for this purpose is generally accepted to be about one gram per kilogram of lean body weight. As meats contain approximately 23 grams of protein per 100 grams, a person weighing, say, 70 kg (11 stone) needs to eat about 300 g (11 oz) of meat, or its equivalent, every day just to supply his basic protein needs. Even eating this volume of lean chicken would provide some 465 calories. These calories are not used to supply energy, they contribute nothing to the body's calorie needs and so must be deducted if you are counting calories.

Much of the fat we eat is also used to provide materials used by the body in processes other than the production of energy: the manufacture of bile acids and hormones, the essential fatty acids for the brain and nervous system, and so on. All these must be deducted as well. Thus trying to determine, from food intake and energy expenditure alone, how much excess energy your body will store as fat will give a completely wrong answer. However, these other factors cannot be measured. Therefore, calorie-counting, which is the foundation of practically every modern slimming diet, is a complete waste of time.

And there is one more flaw: We are told by the 'experts' that 'a calorie is a calorie'. What they mean is that it is impossible for two diets containing exactly the same number of calories to lead to different weight losses. Yet, over the last century a spate of dietary studies has shown that, calorie for calorie, low-carbohydrate diets are much better at reducing weight than the traditional low-fat diets. 'Experts' have heavily criticised these studies saying that the data could not be right because that would violate the laws of thermodynamics. But they don't. It is important to realise that there is more than one law of thermodynamics. The narrow view that 'a calorie is a calorie' might comply with the First Law, but it violates the Second Law of Thermodynamics.

The point is that there is no doubt that low-carb, high-fat diets do have a metabolic advantage when it comes to weight loss, whatever the 'experts' say.[2] And this metabolic advantage complies fully with the second Law of Thermodynamics - and, incidentally, the First Law as well.

The First Law, as mentioned above, is a conservation law. The Second Law is a dissipation law; it is this Second Law which governs the chemical reactions in our bodies.

Let me use an analogy. The energy in the petrol that fuels your car makes the car go along, but it also produces heat through friction and noise, which we really don't need. The Second Law is all about efficiency - how much of the energy we put in does useful work and how much is wasted. Thus, although all of the energy in the petrol is accounted for and complies with the First Law, the actual moving of the car, if the waste products (heat and noise) are removed from the equation, does not. The Second Law was developed in this context. And it applies equally when we look at the efficiency of our bodies and how different foods affect our bodies. The Second Law says that no machine is completely efficient: Some of the available energy is lost as heat or in the internal rearrangement of chemical compounds and other changes. And as different foods use different metabolic pathways, with different levels of efficiency, variations in efficiency must be expected. For this reason, the dogma that a 'calorie is a calorie' violates the second law of thermodynamics as a matter of principle.

It is the differences in chemical changes within our bodies that make low-carb diets better than low-fat, calorie-controlled ones easier to lose weight on. What the diet dictocrats fail to take into consideration when considering the laws of thermodynamics are the energy losses incurred in the different chemical changes within our bodies. When these are taken into consideration, neither law of thermodynamics is violated.

And, if you eat the right foods, you can forget all about counting calories.

1. Kekwick A. The metabolism of fat. J R Coll Gen Pract. 1967; 13 (Suppl 7): 95.
2. Feinman RD, Fine EJ. Thermodynamics and Metabolic Advantage of Weight Loss Diets. Metabolic Syndrome and Related Disorders 2003; 1: 209-219.