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Rumbling tummy? It doesn't mean you need to eat - it's your gut cleaning itself! A new book reveals the astonishing truth about how the human body digests food
Gut: The Inside Story Of Our Body's Most Underrated Organ is out now
Good Health present an extract from book by microbiologist Giulia Enders
Reveals how raw food is 'cooked' in the stomach before being digested
What happens to food after we've eaten? The ins and outs of digestion are not normally considered suitable for polite conversation.
But we should know more about what goes on according to a new book by 25-year-old microbiologist Giulia Enders. Gut: The Inside Story Of Our Body's Most Underrated Organ, is already a bestseller in her native Germany.
And it makes eye-opening reading, as this extract reveals...
From the minute we take our first bite of food, enzymes in saliva start breaking it down. Tiny openings on our cheek secrete saliva even at the thought of food. It has a host of other purposes, too, which is why other openings under the tongue secrete saliva continuously - up to a litre a day.
Saliva is basically blood without the red cells. It contains calcium to help harden our teeth, hormones including oestrogen and testosterone, and perhaps most surprisingly, a natural painkiller, opiorphin, that is stronger than morphine.
Gut: The Inside Story Of Our Body's Most Underrated Organ makes eye-opening reading
This explains why a sore throat often feels better after a meal. There are even a handful of studies showing that opiorphin has antidepressant properties (a new theory is that this painkiller is partly responsible for the reassuring effects of comfort eating).
Saliva also protects the mouth from too many bad bacteria - it contains proteins known as mucins, which envelop our teeth and gums in a protective net.
We shoot out mucins like Spider-Man shoots webs from his wrists. These microscopic nets can catch bacteria before they have a chance to harm us.
But when we are asleep we produce very little saliva - this is the reason many people have bad breath or a sore throat in the morning.
Eight hours of scarce salivation mean one thing for the microbes in our mouth: party time! Bacteria are no longer kept in check - that's why brushing your teeth before you go to bed at night and after you get up in the morning is such a clever idea.
Brushing at bedtime reduces the number of bacteria in your mouth. Brushing in the morning is like cleaning up after a party the night before.
Munching on our first piece of toast or performing our morning dental-hygiene regimen stimulates salivation, and this washes away the nocturnal microbes or transports them down into our stomach, where our gastric juices finish them off.
Steak stays in your tum for six hours
Once chewed food arrives in the stomach, the muscular walls start throwing it around to break it down.
With one big push, food is lobbed against the stomach wall, bounces off it, and plops back down. When the stomach starts merrily swinging to and fro like this, the rest of the digestive tract is galvanised into moving, too.
This leads the gut to move its contents down the line, making room for the next batch. That's why we often feel the urge for the loo after a large meal.
The stomach churns food like this to grind it into tiny particles, most less than 2mm across, before they then pass into the small intestine. Simple carbohydrates, such as cake and sugar, take about two hours to break down.
Proteins and fats remain in the stomach considerably longer. A steak may easily be churned for six hours. This is why meals rich in carbohydrates may perk us up more quickly, but meaty or fatty meals keep us feeling fuller longer.
Digesting proteins requires a burst of energy to break them down - our preference for cooked food is the body's way of outsourcing this task.
The reason we find steak, scrambled eggs, or fried tofu more appetising than raw meat, slimy eggs or cold bean curd is because we have an intuitive understanding of how digestion works.
If we swallowed a raw egg, it would undergo the same processes in our stomach as it would in the frying pan. The white of the egg turns opaque, the yolk takes on a pastel colour, and both set. If we were to vomit the raw egg back up after the right amount of time, the results would look like almost perfect scrambled eggs - without any cooking! Proteins react to the heat in a hot pan and the stomach acid in the same way.
The appendix ISN'T just a waste of space
Just below where the small intestine meets the large intestine is the appendix — it’s made almost entirely of immune tissue and helps keep us healthy by looking out for and attacking bad bacteria from the food we are digesting. A healthy appendix also acts as a storehouse of helpful bacteria. This can be used to re-populate the large intestine after, say, a bout of diarrhoea has washed away our good bacteria.
Digestive juices work like washing powder
The small intestine is three to six metres long and the hardest working part of our digestive tract.
It wants to offer us as much surface area as possible to absorb nutrients from the food, so it is full of folds - without these tiny folds, it would have to be up to 18m long to do its job.
Our digestive juices contain the same agents as washing powder and washing-up liquid; digestive enzymes and fat solvents. Washing powder is effective at removing stains because it 'digests out' any fatty, protein-rich or sugary substances from your laundry, with a little help from the movement of the washing machine drum. That is more or less what happens in our small intestine.
The digestive juices break down carbohydrate, protein and fat. Protein and carbohydrates are transported to the bloodstream through the gut wall, absorbed by blood vessels, and carried to the liver.
Digestive juices contain the same agents as washing powder; digestive enzymes and fat solvents
Here, any dangerous substances are destroyed before the blood passes into the main circulatory system. The nutrient-rich blood then flows from the liver directly to the heart. There, it receives a powerful push and is pumped to the countless cells of our body. The sugar molecules in food can be linked to form complex chains - when that happens, they no longer taste sweet, and we know them as the carbohydrates we find in bread, pasta and rice.
Our digestive enzymes work like tiny pairs of scissors, cutting the chains back into molecules.
The sugar contained in white toast is digested relatively quickly by our enzymes. With wholegrain bread, everything moves at a more leisurely pace, as it contains particularly complex sugar chains.
After that white toast has undergone the snipping of the enzyme scissors, the final product is the same number of sugar molecules as a couple of spoonfuls of ordinary sugar.
The only difference is household sugar can be absorbed directly into the bloodstream, without all that work to digest it. When we eat too much sugar our bodies simply store it away, relinking the molecules to form long, complex chains of a substance called glycogen, which is then stored in the liver.
The average time for food to go from fork to the loo is one day - faster guts accomplish it in eight hours; slower digesters can take three-and-a-half days
Glycogen stores are soon used up - just about the time during your run when you notice the exercise is suddenly much harder work.
That's why nutritional physiologists say we should do at least an hour's exercise if we want to burn fat because we use the glycogen first.
Unlike other nutrients, fat cannot be absorbed straight into the bloodstream. It is not soluble in water, so would clog the tiny blood capillaries of the gut.
This means fat is absorbed via the lymphatic system, a network of thin, transparent-whitish, fluid-filled vessels which drain away fluid pumped out of our tissue, and transport immune cells throughout the body. All the lymph vessels converge in the small intestine, where the digested fat can gather without the risk of clogging anything.
After a meal, the lymph fluid is full of tiny fat droplets, and, whether it is extra-virgin olive oil or cheap chip fat, it is transported straight to the heart, bypassing the liver.
Detoxification of dangerous, bad fat can only take place after the heart has given it a powerful push to pump it through the system, where it ends up in the liver.
But before that happens, our heart and our blood vessels are at the mercy of the fat that fast food chains and manufacturers have been able to get hold of at the lowest purchase price.
Why eating makes you feel sleepy
One reason we feel tired and sluggish after eating is that certain chemical messengers released by the body when we are full also stimulate the areas of the brain responsible for tiredness.
This tiredness is perhaps inconvenient for our brains when we are at work, but the small intestine welcomes it. It works most effectively when we are pleasantly relaxed. It means the optimum amount of energy is available for digestion rather than needing to be used elsewhere, and our blood is not full of stress hormones.
What a rumbling tum REALLY means
Our stomachs rumble when we're hungry - and do so whenever there is a long-enough break between meals to finally get some cleaning done.
Around an hour after the small intestine has finished digesting, a big, noisy, wave-like muscular contraction sweeps any leftovers from the stomach into the intestines to leave the stomach empty and clean. Snacking will stop this process immediately.
Constant snacking means there is no time for cleaning. This is one reason why some nutritional scientists recommend we leave five hours between meals, although there is no scientific evidence proving that the interval must be precisely this period of time.
And are you sure it's tummy ache you have? The stomach begins just under the left nipple, and ends below the bottom of the ribcage on the right - much higher than many people think. Any pain felt lower down cannot be stomach ache. Often when people say they have stomach problems, the trouble is actually in our intestines.
Often when people say they have stomach problems, the trouble is actually in our intestines
How often should you go to the loo?
The large intestine is where the remainder of food that hasn't been digested by the small intestine, such as indigestible fibre, is processed. It doggedly processes these leftovers for 16 hours or so.
In doing so, it helps the body extract substances that would have been lost if the gut were more hurried, including important minerals such as calcium, which can only be absorbed properly here.
It is these bacteria that help produce the gas we pass as wind. Interestingly, alcohol can multiply the number of gas-producing bacteria by a factor of up to 1,000, which is why a night on the town can lead to a morning chorus of the pungent kind.
The average time for food to go from fork to the loo is one day - faster guts accomplish it in eight hours; slower digesters can take three-and-a-half days.
The large intestine has three sections: the ascending, transverse, and descending colon. When we go to the loo, we usually empty the last section. By the next day, it has filled up again.
For most people, the content of their large intestine is enough for one bowel movement a day.
However, people who provide their large intestine with sufficient bulk may have to go to the loo two or three times a day. Faeces is three-quarters water, to ensure it is soft enough to pass easily. Of the solid matter, an astonishing one third is bacteria that our body doesn't need any more.
Another third is made up of indigestible vegetable fibre, and the remaining third is made up of substances your body wants to get rid of - such as the remains of medicines, food colours or cholesterol.
Stool scale
The following Bristol stool scale classifies the consistency of faeces into seven groups. A healthy digestive system will produce types 3 or 4. The other types are less than ideal. If you suffer from regular loose stools or constipation, or have a change in your bowel habits or type of faeces, you should consult your doctor.
Type 1: Separate hard lumps, like nuts (hard to pass).
Type 2: Sausage-shaped, but lumpy.
Type 3: Like a sausage but with cracks on its surface.
Type 4: Like a sausage or snake, smooth and soft.
Type 5: Soft blobs with clear-cut edges, passed easily.
Type 6: Fluffy pieces with ragged edges, a mushy stool.
Type 7: Entirely liquid.
Source: Daily Mail