Andrew Millard wrote:
>
> But both these studies are on diets of average to low calories compared to
> recommended adult intakes.  What's the difference in weight gain between
> people on, say, 4000-calorie and 1000-calorie diets?  It's not surprising
> that at constant calories the composition of the diet can make a
> difference, but reducing calories has an effect too.  It seems incredible
> to me that adults on a 1000-calorie diet could gain weight, as their
> metabolic expenditure ought to exceed this with even a modest amount of
> activity, and if the energy is not coming from burning of body reserves,
> then our fundamental understanding of where biological systems get their
> energy from is in doubt.
>
> Did these studies control for the activity levels and energy expenditure
> of the patients?

I hope you will bear with me as the following is rather long.

That high-energy diets work better for weight loss has often been puzzling,
and it has proved very difficult for dieticians and doctors to accept them
because, on the face of it, they appear to challenge the laws of physics.
But there are several reasons why they do not.

All carbohydrate -- sugars and starches -- contains energy to the value of
four calories per gram and that fat has nine calories per gram.

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.

If we take a gram of carbohydrate and burn it in this way, we get an energy
value of 4.2 calories, or more correctly kilocalories (kcals). If we do the
same with protein, we get a figure of 5.25 kcals. But we must deduct one
calorie because we know that a gram of protein does not oxidise readily and
gives rise to urea and other products to this value which are excreted and
which must be subtracted. That gives a final figure for protein of 4.25
kcals. And if we burn a gram of fat in the bomb calorimeter we get 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 slimmers to measure the amounts that they
may eat. But there are two basic flaws in using these figures to determine
the amounts of food we should eat.

THE FIRST FLAW
The more obvious flaw in the argument is that our bodies do not burn these
foods in the same way that they are burned in a bomb calorimeter. If they
did, we would glow in the dark. In fact the digestive process is quite
inefficient so that all we eat is not even absorbed by the body, let alone
used by it.
 The chemical process, whereby the blood sugar, glucose, is oxidised in the
body to provide energy, gives rise to carbon dioxide that leaves the body
via the lungs as we breathe. Clinicians measure energy use by getting their
subjects to exercise on a treadmill or an exercise bike and measuring the
amount of oxygen breathed in and the amount of carbon dioxide breathed out.
But if you are going to equate energy intake with energy expenditure, you
can only do it if all the carbon leaves the body in this way. But it doesn'
t. In fact, only about half is exhaled as carbon dioxide, the other half is
excreted in sweat, urine and faeces as energy-containing molecules: urea,
lactates and pyruvates, the energy values of which must be deducted from the
original food intake.
All of these can vary from time to time and they also vary with the types of
food eaten. We know, for example, that if a lot of fat is eaten, it puts
ketones into the urine. And we know that the value of a gram of ketones
derived from fat is roughly four calories. So, in this case, nearly half the
energy from fat goes, not into providing the body with energy, but down the
toilet.

THE SECOND FLAW
Nutritionists frequently liken eating food to putting petrol in a car --
simply treating food as fuel. But this concept is quite wrong. Unlike the
car, your body has the ability to repair and renew itself, for which it uses
proteins, fats and other nutrients found in food. The second and more
important flaw in the argument, therefore, is that your body does not use
all the food it has available merely to provide energy.

All edible carbohydrates have but one purpose: to supply calories that your
body can use for energy. Counting them might have some point, as they do
nothing else. But while the body can use proteins and fats to provide
energy, they do very much more -- in ways that do not involve the production
of energy.

Body cells are in a constant state of death and rebirth. No matter how many
birthdays you have had, very little of you is more than eight years old. The
primary function of dietary proteins is used in this process: for the
manufacture and repair of skin, blood and other body cells; to make hair and
finger- and toe-nails. 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 stones) needs to eat about 300 g (11 oz) of meat,
or its equivalent, every day just to supply his basic protein needs. Even
eating lean chicken this would contain 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, how much
excess energy your body will store as fat will give a completely wrong
answer unless these other factors are known and allowed for. But how do you
measure these? The simple answer is: you can't. There is no point,
therefore, in trying. And calorie counting, which is the foundation of
practically every modern slimming diet is a complete waste of time.

Andrew wrote:
>
> Overweight lions will fail to catch food even if it is abundant, and then
> they will become thinner lions.  One might equally ask how many fat koalas
> does one see? None and they are vegetarian, move slowly and have an
> abundant food supply.  Just because another species is not seen to be
> over-weight does not make it a good analogue for humans.  What evidence is
> their that humans are carnivores rather than omnivores?
>

You are quite right that I could have looked at another species, because ALL
animals in their natural habitat are a normal weight. But, then, all of them
consume a diet that is natural to them without anyone having to tell them
what, when and how much to eat.

The evidence for our being carnivores is contained within us: our
gastrointestinal tract. As biochemistry textbooks are not the easiest books
to read, see Walter Voegtlin's book, "The Stone Age Diet", published in
1976, for a masterful treatise on the subject.

Barry Groves
http://www.second-opinions.co.uk