John_Yudkin_-_Pure_White_and_Deadly_revised_1986_OCR

Pure, White and Deadly
protein foods; human beings will soon be able to feed themselves
entirely with synthetic protein and other nutrients. And this at a
time when new facts are discovered almost daily about such supposedly
well-understood phenomena as obesity, or about the effects of
different dietary carbohydrates. The safest position is somewhere
between arrogance based on unrecognized ignorance, and arrogance
based on unwarranted certainty.
But how do we find this position? What sorts of principles do we
adopt in order to decide whether this or that food is 'good for you'?
What indeed should the ideal diet be?
I am going to devote the rest of this chapter to trying to answer
these questions, slowly and carefully, because I believe that an
understanding of the biology of the diet provides the clues to what
the western diet should be; what is wrong with it today; and why it
has gone wrong.
We begin by reminding ourselves that all animals require two
sorts of materials for their growth and survival. One is material that
can be burned (oxidized) to yield the energy needed for the processes
of living - growth and movement and breathing, and all the other
activities that distinguish a living animal from a dead one. These
materials for energy production are mainly carbohydrates and fats,
although protein can also be used in this way. The second sort of
material consists of those thousands of different compounds that go
to make up the very complex chemical composition of the cells of
the different tissues that, organized together, constitute the whole
living animal. The vast majority of these compounds can be made
by the body itself, from a very much smaller number of raw
materials. But these are all materials that must, each one of them,
be supplied to the body. Without them, a young organism cannot
grow, and an adult organism will gradually waste away because it is
unable to make good the general wear and tear of its cells and tissues.
So we can say at this point that the body has to be given materials
both to supply energy and to provide the 'raw materials for growth
and repair. The source of these essential materials is our food and
drink. These have to supply about 50 different items. They fall
into several classes - the carbohydrates, the fats, the proteins, the
vitamins, the mineral elements - and of course water.
As far as we know, every single species of animal needs the same
components for life and sustenance. And almost every single species
has to get all of these out of food. The exceptions are interesting,
and include ruminants like cows which can get many vitamins from
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I eat it because I like it
microbes living in their complicated stomachs. But in general, as I
said, most animals have to get all of their vitamins, protein and so
on from their food, and these nutrients are needed in roughly the
same proportions by all animal species.
You could therefore argue that all species of animals should eat
the same foods. But in fact it is well known that different species
. eat very different diets indeed. Some, like the lion and the tiger, are
largely carnivorous - meat-eating. Others, like rabbits and giraffes
and deer, are largely herbivorous - plant-eating or vegetarian.
Others again, like ourselves and rats and pigs, eat diets that come
from both animal and plant sources; these animals are omnivorous.
By contrast some animals eat only a very limited range of foods; the
giraffe eats little except leaves from acacia trees. The koala bear eats
little except eucalyptus leaves, and then only from a few of the 400
or so existing species.
So there is an apparent contradiction. First, all species of animals
require the same in the way of nutrients, which - with a few exceptions
- they must get from their food. But secondly, different species
of animals get these same nutrients from very different sorts of diet.
Great biological advantages flow from this, because it prevents the
various species competing with each other for the same foods. Each
species establishes its own 'ecological niche' in regard to its food
supply. Its anatomy and physiology are well adapted to find,
acquire, eat, chew and digest the foods that it chooses.
But the fact remains that one species will often not even attempt
to eat foods that are highly sought after by another species. So what
makes one animal choose one sort of diet, and a different animal
choose a completely different sort? Clearly, it cannot be that they
are choosing these different foods for the nutrients they contain,
since their nutrient needs are so similar. It must therefore be some
other properties of foods that make one range of foods look specially
attractive to one species, and another range especially attractive to
another. These qualities are shape and size, colour and smell, taste
and texture - features that I'd like to lump together, perhaps too
loosely, under the heading of palatability.
Foods thus possess two different properties - palatability and
nutritional value. The palatability of foods, and so the foods chosen
to make up the total diet, varies from species to species; however,
the nutritional needs that have tp be satisfied by these various species
are virtually the same for all species. Thus, animals choose diets that
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