WHY LOW-CARB DIETS MUST BE HIGH-FAT, NOT HIGH-

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WHY LOW-CARB DIETS MUST BE HIGH-FAT, NOT HIGH-PROTEIN

WHY LOW-CARB DIETS MUST BE HIGH-FAT, NOT HIGH-PROTEIN

Fat is the most valuable food known to Man

PROFESSOR JOHN YUDKIN

Introduction

We now know that we should eat a diet that is low in carbohydrates. But a

plethora of books published in the last decade have been low-carb,

high-protein,

or low-carb, high-fat, or low-carb, high-‘good’-fats, or all sorts of other

mixtures. In other words, the real confusion lies in what we should replace

the carbohydrates with: for example, should it be protein or fats? And if

fats, what sort of fats? This article, I hope, will answer the question and

put

any doubts out of your mind. In a nutshell, carbs should be replaced with

fats, and those fats should be mainly from animal sources.

Our bodies use carbs for only one purpose: to provide energy. When we cut

down on carbs, the energy our bodies need has to come from somewhere else.

There are only two choices: Protein or fat.

ATP: our bodies’ fuel

The fuel that our body cells use for energy is actually neither glucose nor

fat, it is a chemical called adenosine triphosphate (ATP). A typical human

cell

may contain nearly one billion molecules of ATP at any one moment, and those

may be used and re-supplied every three minutes. This huge demand for

ATP,

and our evolutionary history, has resulted in our bodies’ developing several

different pathways for its manufacture.

Oxygen and mitochondria

Living organisms have two means to produce the energy they need to live. The

first is fermentation, a primitive process that doesn’t require the presence

of oxygen. This is the way that anaerobic (meaning ‘without oxygen’)

bacteria break down glucose to produce energy. Our body cells can use this

method.

The second – aerobic (meaning ‘using oxygen’) – method began after the Earth

began to cool down and its atmosphere became rich in oxygen. After this

event,

a new type of cell – a eukaryotic cell – evolved to use it. Today all

organisms more complex than bacteria use this property and all animal life

requires

oxygen to function. When we breathe in, our lungs are used to extract the

oxygen in air and pass it to the bloodstream for transport through the body.

And in our bodies, it is our body cells’ mitochondria – little power plants

that produce most of the energy our bodies need – that use this oxygen. The

process is called ‘respiration’. This process takes the basic fuel source

and oxidises it to produce ATP. The numbers of mitochondria in each cell

varies,

but as much as half of the total cell volume can be mitochondria. The

important point to note is that mitochondria are primarily designed to use

fats.

Which source of base material is best?

The question now, in this era of dietary plenty, is: Which source is

healthiest? There are three possible choices:

glucose, which comes mainly from carbohydrates, although protein can also be

utilised as a glucose source by the body if necessary;

Fats, both from the diet and from stored body fats;

Ketones which are derived from the metabolism of fats

Not all cells in our bodies use the same fuel.

Cells that can employ fatty acids are those that contain many mitochondria:

heart muscle cells, for example. These cells can make energy from fatty

acids,

glucose, and ketones, but given a choice, they much prefer to use fats.

Cells that cannot use fats must use glucose and/or ketones, and will shift

to preferentially use ketones. These cells also contain mitochondria.

But we also have some cells that contain few or no mitochondria. Examples of

cells with few mitochndria are white blood cells, testes and inner parts of

the kidneys; and cells which contain no mitochondria are red blood cells,

and the retina, lens and cornea in the eyes. These are entirely dependent on

glucose and must still be sustained by glucose.

This means that when we limit carb intake, the same energy sources must be

used, but a greater amount of energy must be derived from fatty acids and

the

ketones derived from fatty acids, and less energy from glucose.

Sources of glucose

To understand how a low carb diet works, we need to look at how we eat. This

process is one of eating, digestion, hunger and eating again. During our

evolution,

we also must have experienced long periods when food was in short supply and

we starved. This is a pattern our bodies are adapted to. And they have

developed

mechanisms to cope with a wide range of circumstances. Firstly, the human

body must contain adequate levels of energy to sustain the essential body

parts

that rely on glucose. The brain and central nervous system may be a

particular case as, although the brain represents only a small percentage of

body weight,

it uses between twenty and fifty percent of all the resting energy used by

the body.[ii] Fortunately the brain can also use ketone bodies derived from

fats. During fasting in humans, and when we are short of food, blood glucose

levels are maintained by the breakdown of glycogen in liver and muscle and

by the production of glucose primarily from the breakdown of muscle proteins

in a process called gluconeogenesis, which literally means ‘glucose new

birth’.[iii]

But we don’t want to use lean muscle tissue in this way: it weakens us. We

want to get the glucose our bodies need from what we eat. Some of that will

come

from carbs, the rest from dietary proteins. Our bodies need a constant

supply of protein to sustain a healthy structure. This requires a fairly

minimal

amount of protein: about 1 to 1.5 grams per kilogram of lean body weight per

day is all that is necessary to preserve muscle mass.[iv] Any protein over

and above this amount can be used as a source of glucose.

Dietary proteins are converted to glucose at about fifty-eight percent

efficiency, so approximately 100g of protein can produce 58g of glucose via

gluconeogenesis.[v]

During prolonged fasting, glycerol released from the breakdown of

triglycerides in body fat may account for nearly twenty percent of

gluconeogenesis.[vi]

Body fats are stored as triglycerides, molecules that contain three fatty

acids combined with glycerol. The fatty acids are used directly as a fuel,

with

the glycerol stripped off. This is not wasted. As the glycerol is nearly ten

percent of triglyceride by weight and two molecules of glycerol combine to

form one molecule of glucose, this also supplies a source of glucose.

The case for getting energy from fat and ketones

When most people think of eating a low-carb diet, they tend to think of it

as being a protein-based one. This is false. All traditional carnivorous

diets,

whether eaten by animals or humans, are more fat than protein with a ratio

of about eighty percent of calories from fat and twenty percent of calories

from protein. Similarly, the main fuel produced by a modern low-carb diet

should also be fatty acids derived from dietary fat and body fat. We find in

practice that free fatty acids are higher in the bloodstream on a low-carb

diet compared with a conventional diet.[vii] [viii]

But fats also produce an important secondary fuel: ‘ketone bodies’. Ketones

were first discovered in the urine of diabetic patients in the mid-19th

century;

for almost fifty years thereafter, they were thought to be abnormal and

undesirable by-products of incomplete fat oxidation. In the early 20th

century,

however, they were recognised as normal circulating metabolites produced by

liver and readily utilised by body tissues. Ketones are an important

substitute

for glucose. During prolonged periods of starvation, fatty acids are made

from the breakdown of stored triglycerides in body fat.[ix] On a low-carb

diet,

the fatty acids are derived from dietary fat, or body fat if the diet does

not supply enough. Free fatty acids are converted to ketones by the liver.

They

then provide energy to all cells with mitochondria. Within a cell, ketones

are used to generate ATP. And where glucose needs the intervention of

bacteria,

ketones can be used directly. Reduction of carbohydrate intake stimulates

the synthesis of ketones from body fat.[x] This is one reason why reducing

carbs

is important. Another is that reducing carbohydrate and protein intake also

leads to a lower insulin level in the blood. This, in turn, reduces the

risks

associated with insulin resistance and the Metabolic Syndrome.

Ketone formation and a shift to using more fatty acids also reduces the body’s

overall need for glucose. Even during high-energy demand from exercise, a

low-carb diet has what are called ‘glucoprotective’ effects. What this all

means is that ketosis arising from a low-carb diet is capable of

accommodating

a wide range of metabolic demands to sustain body functions and health while

not using, and thus sparing, protein from lean muscle tissue. Ketones are

also the preferred energy source for highly active tissues such as heart and

muscle.[xi]

All this means that more glucose is available to the brain and other

essential glucose-dependent tissues.

The case against getting energy from protein

We know, then, that dietary fats can produce all the energy the body needs,

either directly as fatty acids or as ketone bodies. But, as there is still

some

debate about the health implications of using fats, why not play safe and

eat more protein?

There is one simple reason: While the body can use protein as an energy

source in an emergency, it is not at all healthy to use this method in the

long

term. All carbs are made up of just three elements: carbon, hydrogen and.

oxygen. All fats are also made of the same three elements. Proteins,

however,

also contain nitrogen and other elements. When proteins are used to provide

energy, these must be got rid of in some way. This is not only wasteful, it

can put a strain on the body, particularly on the liver and kidneys.

Excess intake of nitrogen leads in a short space of time to hyperammonaemia,

which is a build up of ammonia in the bloodstream. This is toxic to the

brain.

Many human cultures survive on a purely animal product diet, but only if it

is high in fat.[xii] [xiii] A lean meat diet, on the other hand cannot be

tolerated;

it leads to nausea in as little as three days, symptoms of starvation and

ketosis in a week to ten days, severe debilitation in twelve days and

possibly

death in just a few weeks. A high-fat diet, however, is completely healthy

for a lifetime.

Perhaps one of the best documented studies is that of the Arctic explorer,

Vilhjalmur Stefansson and a colleague.[xiv] They ate an animal meat diet for

more than a year to see whether such a diet could be healthy. Everything was

fine until they were asked to eat only lean meat. Dr McClelland, the lead

scientist, wrote:

Block quote start

‘At our request he began eating lean meat only, although he had previously

noted, in the North, that very lean meat sometimes produced digestive

disturbances.

On the third day nausea and diarrhea developed. When fat meat was added to

the diet, a full recovery was made in two days.’

Block quote end

This was a clinical study, but Stefansson had already lived for nearly

twenty years on an all-meat diet with the Canadian Inuit. He and his team

suffered

no ill effects whatsoever.

Low-carb, high-fat diet and weight loss

There is just one other consideration: If you want to lose weight, the

actual material you want to rid your body of is fat. But to do that you have

to change

your body from using glucose as a fuel to using fat – including your own

body fat. This is another reason not to use protein as a substitute for

carbs,

as protein is also converted to glucose.

If you think about it, Nature stores excess energy in our bodies as fat, not

as protein. It makes much more sense, therefore, to use what we are designed

by Nature to use. And that is fat.

So what levels of carbs, fats and proteins are required?

Clinical experience and studies into low-carb diets over the last century

suggest that everybody has a threshold level of dietary carbohydrate intake

where

the changeover from glucose-burning to fat and ketone burning takes place.

This varies between about sixty-five and 180 grams of carbs per day.[xv] If

your carb intake is below this threshold, then your body fat will be broken

down to generate ketones to supply your brain and other cells that would

normally

use glucose. In the early trials for the treatment of obesity, carb levels

were very much reduced to supply only about ten percent of calories. This

works

out at around fifty or sixty grams of carb for a 2,000 calorie daily intake.

For diabetics, the level may need to be lower to counteract insulin

resistance. Typical levels of carb intake for a type-2 diabetic are around

fifty grams

per day; the level should be lower still at about thirty grams a day for a

type-1 diabetic.

A Polish doctor, Jan Kwasniewski, who has used a low-carb diet to treat

patients with a wide range of medical conditions for over thirty years,

recommends

a ratio of one part carb to two parts protein to between three and four

parts fat, by weight. I see no reason to disagree with this. What it means

in practice

is that on a 2,000 calorie per day diet, we should get:

Block quote start

Ten to fifteen percent of calories from carbs

Twenty to thirty percent of calories from protein and

Sixty to seventy percent of calories from fats.

Block quote end

Or put another way, as it is difficult to work out percentages in this way,

fifty to seventy-five grams of carb and the rest from meat, fish, eggs,

cheese,

and their natural fats.

Potential for other diseases

The traditional Inuit (Eskimo) diet is a no-carb diet. It is notable that

the Inuit diet described by Drs Vilhjalmur Stefansson and Hugh Sinclair in

the

1950s is very similar in regard to percentages of fat/protein/carb intake to

the experimental low-carb diets used in recent obesity studies.[xvi] The

Inuit

diet was comprised of seal, whale, salmon, and a very limited amount of

berries and the partially digested contents of animals’ stomachs. On this

diet,

blood cholesterol levels were very high as were free fatty acids, but – and

this in much more important – triglycerides were low.[xvii] [xviii] It is

interesting

to note that the Inuit were of great interest to research scientists because

they had practically none of the diseases we suffer, including obesity,

coronary

heart disease and diabetes mellitus.[xix] [xx]

References

. Alberts B. Molecular Biology of the Cell, edn 4. New York: Garland

Science; 2002: p 93.

[ii]. Cahill GF. Survival in starvation. Am J Clin Nutr 1998; 68:1–2.

[iii]. Exton JH. Gluconeogenesis. Metabolism 1972; 21:945–990.

[iv]. Volek JS, Sharman MJ, Love DM, et al. Body composition and hormonal

responses to a carbohydrate-restricted diet. Metabolism 2002; 51:864–870

[v]. Krebs HA. The metabolic fate of amino acids. In Mammalian Protein

Metabolism, vol 1, Munro HN, JB, eds. New York: Academic Press,

1964:164

[vi]. Vazquez JA, Kazi U. Lipolysis and gluconeogenesis from glycerol during

weight reduction with very low calorie diets. Metabolism 1994; 43:1293–1299.

[vii]. Phinney SD, Bistrian BR, Wolfe RR, Blackburn GL. The human metabolic

response to chronic ketosis without caloric restriction: physical and

biochemical

adaptation. Metabolism 1983; 32:757–768.

[viii]. Bisshop PH, Arias AM, Ackermans MT, et al. The effects of

carbohydrate variation in isocaloric diets on glycogenolysis and

gluconeogenesis in healthy

men. J Clin Endocrinol Metab 2000; 85:1963–1967.

[ix]. Cahill GF Jr. Starvation in man. N Engl J Med 1970; 19:668–675.

[x]. Klein S, Wolfe RR. Carbohydrate restriction regulates the adaptive

response to fasting. Am J Physiol 1992; 262:E631–E636.

[xi]. Neely JR, HE. Relationship between carbohydrate and lipid

metabolism and the energy balance of heart muscle. Annu Rev Physiol 1974;

36:413–459.

[xii]. Speth, D. and A. Spielmann 1982 Energy source, protein

metabolism, and hunter-gatherer subsistence strategies. Journal of

Anthropological

Archaeology 2:1-31.

[xiii]. Noli & Avery. Protein poisoning and Coastal Subsistence. J Archaeol

Sci. 1988; 15:395-401

[xiv]. McClelland, et al. Clinical Calorimetry: XLV, XLVI, XLVII. Prolonged

Meat Diets...... J Biol Chem 1930-31; 87:651, 87:669, 93:419

[xv]. Klein S, Wolfe RR. Op cit.

[xvi]. Stefansson V. The Fat of the Land. Macmillan Press, New York, 1957.;

Sinclair HM: The diet of Canadian Indians and Eskimos. Proc Nutr Soc 1952,

12:69–82.

[xvii]. Bang HO, Dyerberg J, Nielsen AB: Plasma lipid and lipoprotein

pattern in Greenlandic West-Coast Eskimos. Lancet 1971; I:1143–1146.

[xviii]. Feldman SA, Ho KJ, LA, et al. Lipid and cholesterol

metabolism in Alaskan arctic Eskimos. Arch Pathol 1972; 94:42–58.

[xix]. Bjerregaard P, Dyerberg J: Mortality from ischaemic heart disease and

cerebrovascular disease in Greenland. Int J Epidem 1988, 17:514–519.

[xx]. Sagild U, Littauer J, Jespersen CS, Andersen S: Epidemiological

studies in Greenland 1962–1964. I. Diabetes mellitus in Eskimos. Acta Med

Scand 1966,

179:29–39.

Last updated 11 June 2005

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