Never Mind the Bullocks, Here's the Science (19 page)

If you really want high efficiency in converting food to body mass, ignore cattle with their pathetic 10% conversion efficiency. Eat cockroaches, which convert 44% of their food to body mass. Or you might prefer chickens, which are pretty good at food-to-body mass conversion as well.

Meat Rots Before Elimination?

Here’s the claim: ‘It is a known fact that eating flesh of dead animals is hard to digest and some of it rots in the gut before elimination can take place and this putrefying residue is absorbed into the bloodstream and it poisons the entire system.’ In human beings this ‘poison’ is supposed to cause ‘…premature ageing, fatigue, toxicity and worms feasting on this waste. The cells of the
body must be supplied with the proper nourishment to efficiently eliminate this waste and when something blocks this process, the cells and organs deteriorate and die. By the time meat eaters reach the age of 50 years they will have accumulated a lot of undigested meat rotting in their gut.’

There is a particularly American version of this on the wonderful Urban Myths home page (snopes.com). It says: ‘By the way, when they did an autopsy on John Wayne (Mr Macho himself) 40 pounds [18.14 kg] of impacted fecal matter was removed from his death-inducing cancerous colon. That’s because Humans are not evolved for Animal eating.’

This is a complete fabrication, as Snopes points out furhter in their article. At the time of his death in 1979, the actor John Wayne
was an American icon. He had already undergone several surgical operations for his cancer, which eventually killed him. It was obvious from his clinical course that the cancer killed him, so there was no medical or forensic reason for an autopsy. In fact, his family was so intent on keeping the fans and the media at bay that they had his body secretly transferred to a mortuary at 5.45 am for a quick funeral service, and then buried him immediately, without an identifying headstone. There was no autopsy and, hence, no ‘40 pounds of impacted fecal matter’ to be found.

Evolved to Eat Meat

One variation of this Rotting Meat myth includes the assertion that the average American stores (presumably until they die) several kilograms of ‘undigested, putrefying meat’ in their intestines. The supposed reason for this is that human beings were not designed to eat meat.

But we have evolved to eat meat. Here’s some proof.

First, the teeth in the human skull include both cutting incisors (as found in carnivores) and grinding molars (as found in herbivores). This combination makes us flexible omnivores. The incisors can generate an effective ‘squash’ of 2-3 kg, while the molars can generate about 90 kg.

In addition, the human gut has all the enzymes needed to digest meat.

Human beings have quite a long, and sophisticated, gut. Our stomachs probably evolved about 500 million years ago. Before then creatures had no jaws, so they would slowly digest all that they could swallow. However, with the development of the jaw, prehistoric fishes needed somewhere to store the stuff they had eaten and so developed a gut.

Enzyme and Surface

An enzyme is a chemical that makes a chemical reaction happen more quickly. Breaking down carbohydrates, fats and proteins into their constituent molecules happens through chemical reactions. So, of course, enzymes are involved.

Now here’s a very fundamental truth of biochemistry.

Enzymes work only on a surface.

Enzymes can act
only
on chemicals that they can get close to, i.e. chemicals on a surface of something. So if you just swallow your food without chewing it, the enzymes in your gut can break down the carbohydrates, fats and proteins on the surface of the ball of food. They cannot break down any carbohydrates, fats and proteins deep inside the ball of food – because they cannot get to them.

So part of the process of digestion is breaking down your food into smaller balls which, in total, have a bigger surface area. Chewing your food thoroughly can help digestion.

We Have Evolved to Eat Meat

The teeth in our skulls include both cutting incisors (as found in carnivores) and grinding molars (as found in herbivores).

This combination makes us flexible omnivores.

The incisors can generate an effective ‘squash’ of 2-3 kilograms, while the molars can generate about 90 kilograms.

Digestion

The human gut is approximately 10 m long. The food enters at the mouth where you chew it, and where your saliva adds a few digestive enzymes. Then, after transit via the oesophagus, this food ends up in the stomach.

In the stomach, the enzyme called ‘pepsin’ attacks the proteins in meat. Pepsin has two main pathways of activity. First, it attacks collagen that makes up the main bulk of the connective tissue that joins the cells of the meat together. This allows the pepsin to get into the cells of the meat. Second, once it gets inside these cells,
pepsin starts breaking down the long chains of amino acids into smaller chains.

Typically, some of the food will leave the stomach almost immediately. (We know that some carbohydrate foods leave the stomach almost immediately, because the blood glucose levels are already higher than fasting levels within 5-10 minutes of eating.) Overall, food will stay in the stomach for up to two and a half hours, before moving on to the next section, the small intestine. But the pepsin acting in the stomach digests only about 15% of the protein.

The small intestine does most of the digestion and absorption of what we eat. It takes about 2-6 hours to do so.

The pancreas is an organ that squirts various enzymes into the small intestine. These enzymes are very powerful, able to digest fats and carbohydrates, as well as proteins. With proteins, they break down the small chains of amino acids into even smaller chains. These enzymes are ‘activated’ only after they have been squirted out into the hollow tube of the small intestine—because they are so powerful that they can digest even the pancreas itself.

Bring on the Surface Area

The small intestine can absorb only via its internal surface. So it has lots of ‘tricks’ to increase its internal surface area.

First, it is not just a simple tube with a constant diameter. It has visible internal folds or pockets, called ‘valvulae conniventes’ (or the ‘Folds of Kerckring’), which protrude as much as 8 mm into the internal ‘lumen’ (the hollow part of the tube). These folds increase the surface area by a factor of three.

Second, there are literally millions of small fingers, called villi, covering the surface of the small intestine. About 1 mm high, they increase the surface area by another factor of ten.

Third, the villi in turn are covered by microvilli, as many as 1,000 to each cell lining the gut. These microscopic fingers are about 1 micrometre long (one-millionth of a metre) and 0.1 micrometres thick. They increase the internal surface area a further 20 times.

So the total internal surface area of the small intestine is increased by a factor of about 1,000, to about 250 m
²
, roughly equal to the area of a tennis court.

Meat My Stomach

THE STOMACH

In the stomach, the enzyme called ‘pepsin’ attacks the proteins in meat. Pepsin has two main pathways of activity. First, it attacks collagen that makes up the main bulk of the connective tissue joining the cells of the meat together. This allows the pepsin to get into the cells of the meat. Second, once it gets inside the cells of which meat is made, pepsin starts breaking down the long chains of amino acids into smaller chains.

Water and Digestion

Water is probably the only chemical for which practically everybody knows the formula – H
₂
O. (And perhaps the now infamous greenhouse gas, C0
₂
, is also in the process of becoming as well known.)

The reaction to make, and break, water can run in either direction, depending on where energy is applied.

This same reaction is essential for breaking down all three major foods – carbohydrates, fats and proteins.

Carbohydrates are made of repeating single sugars stuck together. The breakdown reaction involves taking an ‘H’ from one sugar, and an ‘OH’ from the next sugar, and so on. The ‘H’ and the ‘OH’ combine to make water, H
₂
O. So breaking down carbohydrates generates water.

Breaking down fats also makes water. (This is how camels survive – their hump is full of fat, not water.) A fat usually has three fatty acid molecules combined with a glycerol molecule. When they are split, three molecules of water are released.

Proteins are different – they need the addition of water to break them down. (Ever felt thirsty after a high-protein meal?) Proteins are strings of amino acids stuck together. To separate them, an ‘H’ is added to one amino acid, an ‘OH’ is added to the next, and so on.

The small intestine has a big job. Each day, it has to digest some 7-8 litres of liquid.

This liquid consists of about 1,000 ml of saliva from the mouth, 1,500 ml from the stomach, 1,000 ml from the pancreas, 1,000 ml of bile from the gall bladder, 1,800 ml from the small intestine itself and 200 ml from Bruner’s Gland (located in the first few centimetres of the duodenum). Each day, your small intestine will absorb ‘several hundred grams of carbohydrates, about 100 g of fat, 50-100 g of amino acids, 50-100 g of ions and 7-8 litres of water’.

Running at maximum capacity, each day it can absorb several kilograms of carbohydrates, 500 g of fat, about 600 g of protein and over 20 litres of water!

Break Down

The cells lining the gut have microscopic fingers on them called microvilli.

Enzymes are anchored or embedded in the actual walls of the microvilli. These enzymes start inside the body of the microvilli, and protrude through the wall of the microvilli into the hollow tube of the gut.

When you eat food, these enzymes break down the chains of amino acids (in the meat) into tiny chains of three and two amino acids and, sometimes, even single amino acids. These are carried into the cells lining the gut and broken down (if necessary) into single amino acids. Then they are passed right through the cell out to the other side, and then into a vein that carries the individual amino acids to the Big Organ, the liver, for further processing.

The gut contents are then moved from the small intestine into the large intestine where water and some electrolytes are removed. The time taken for this transit is much greater, ranging from 14 to 80 hours.

The various transit times are affected by many factors, including genetics, quantity of fibre in the diet, size of meals, age, gender, smoking, exercise, and so on.

So yes, our human gut actually has all the mechanisms needed for digesting the proteins of meat.