分节阅读 Table of contents

• 1.What We Really Eat

  • The most important phase of our digestion takes place in the small intestine, where the maximum surface area works on the maximum reduction of our food down to the tiniest pieces. This is where the decisions are made. Can we tolerate lactose? Is this food good for our health? Which food causes allergic reactions? Here, in this final stage of breakdown, our digestive enzymes work like tiny pairs of scissors. They snip away at our food until it shares a lowest common denominator with our cells. Canny as ever, Mother Nature here makes use of the fact that all living things are made out of the same basic ingredients: sugar molecules, amino acids, and fats. Everything we eat comes from living things— at this biological level, there is no difference between an apple, a tree, and a cow.  
    
    Sugar is an important raw material for our body. It is used as fuel for our cells— like heat-giving firewood— or to build sugar structures for use in our body, such as the antler-like glycocalyxes attached to our gut cells. Sugar can be turned into energy extremely quickly, and our brain rewards us for this rush of rapid energy by making us feel good. However, there is one problem: never before, in the history of humankind, have we been faced with such a huge abundance of readily available sugar. Some 80 percent of the processed foods found on the shelves of modern-day American supermarkets contain added sugar. It partly explains the serious obesity issue happening in the U.S. today.
    
    Many studies have been carried out on the effects of olive oil, and results show that it can protect against arteriosclerosis, cellular stress, Alzheimer’s, and eye diseases such as macular degeneration. It also appears to have beneficial effects on inflammatory diseases such as rheumatoid arthritis. It may help in protecting against certain kinds of cancer. However, when families consume olive oil everyday, they use it in the wrong way. Merrily drizzling your olive oil into the pan for frying is not such a good idea as heat can cause a lot of damage. Hot plates are great for frying up steaks or eggs, but they are not good for oily fatty acids, which can be chemically altered by heat. Cooking oil or solid fats such as butter or hydrogenated coconut oil should be used for frying. Fine oils are not only sensitive to heat, they also tend to capture free radicals from the air. Free radicals do a lot of damage to our bodies, that’s why you should always close the bottle or container of olive oil carefully after use and keep it in the fridge. 
    
    The animal fats found in meat, milk, and eggs contain far more arachidonic acid than vegetable fats. Arachidonic acid is converted in our body into neurotransmitters involved in the sensation of pain. Large amounts are simply too much for the body to deal with. It’s comparable to smearing too much moisturizer on your face. Nutritional physiologists recommend we get between 25 and a maximum of 30 percent of our daily energy requirement from fat. That works out at an average of 2 to 2 ½ ounces (55 to 66 grams) of fat a day. This means if you eat just one Big Mac, you will have already satisfied half your daily requirement of fat.
    
    However, maintaining a healthy meat-free diet that does not lead to nutritional deficiencies is more difficult than most people think. Plants construct different proteins than animals, and they often use so little of a given amino acid that the proteins they produce are incomplete. Beans lack the amino acid methionine; rice and wheat lack lysine; and sweet corn is, in fact, deficient in two amino acids: lysine and tryptophan. But this does not spell the final triumph of the meat eaters over the meat avoiders. Vegetarians and vegans simply have to be smarter when combining their foods. 
    
    For centuries in many countries around the world, people have intuitively eaten meals made up of foodstuffs that complement each other: rice and beans, pasta with cheese, pita bread and hummus, or peanut butter on toast. In theory, combining does not even have to take place within one meal. It is enough to eat the right combination over the course of a day. There are plants that do contain all the necessary amino acids in the necessary quantities. Two of these are soy and quinoa, but others include amaranth, spirulina, buckwheat, and chia seeds. Tofu has a well-deserved reputation as an alternative to meat— with the caveat that increasing numbers of people are developing allergic reactions to it.

• 2.Magical Saliva

  • From the minute we take our first bite of food, the enzymes in saliva start breaking it down. Tiny openings in 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 liter a day.
    
    Saliva is basically blood without the red cells. It contains calcium to help harden our teeth, hormones including estrogen and testosterone, and perhaps most surprisingly, a natural painkiller, opiorphin, that is stronger than morphine. 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. Saliva also protects the mouth from harmful 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 so important. 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. Luckily, our salivary glands wake up at the same time we do in the morning and start production straight away.

• 3.Cooking eggs in stomach?

  • 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 galvanized into moving too.
    
    This leads the gut to move its contents down the line, making room for the next batch. The stomach churns food like this to grind it into tiny particles, most less than 2mm across, before they 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 appetizing 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 and the yolk takes on a pastel color. 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 our stomach acid in the same way.

• 4.Digestive Juices Work Like Laundry Detergent

  • The small intestine is three to six meters 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 laundry detergent and dish soap: digestive enzymes and fat solvents. Laundry detergent is effective at removing stains because it breaks down 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 carbohydrates, proteins and fat. Proteins and carbohydrates are transported to the bloodstream through the gut wall, absorbed by blood vessels, and carried to the liver. 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 in comparison with whole grain bread that makes everything move more slowly, as it contains particularly complex sugar chains. After the 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 that household sugar can be absorbed directly into the bloodstream, without all the 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. 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 and therefore clogs up 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 transports 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.

• 5.What a Rumbling Tum Really Means

  • The small intestine is a stickler for cleanliness. It is like someone who cleans up the kitchen right after a meal. An hour after the small intestine has digested something, it begins the clean-up process. The scientific name for this process is “migrating motor complex.” When it kicks in, the stomach doorman is kind enough to open the gates again to allow these leftovers to be herded into the small intestine. It then moves them along with a wave powerful enough to sweep everything along with it. When observed with a camera, this looks so cute that even sober-minded scientists can’t help but nickname the migrating motor complex the little “housekeeper.” 
     
    Everyone has heard the little housekeeper at work. It is the rumbling belly, which, contrary to popular belief, does not come mainly from the stomach, but from the small intestine. We don’t necessarily always hear the housekeeper at work. It depends on how much air has found its way into the stomach and the small intestine. If we eat something before the cleanup is finished, the housekeeper immediately stops working and returns to waiting mode. Snacking will stop this process immediately. Constant snacking means there is no time for cleaning. This is part of the reason some nutritional scientists recommend we leave five hours between meals, but at the same time there is no scientific evidence proving that the interval must be precisely five hours. 
     
    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 a stomach ache. Often when people say they have stomach problems they don’t realize that the trouble is actually in our intestines.

• 6.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 fiber, is processed. It slowly 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 in a hurry, 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. Human waste 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 fiber, and the remaining third is made up of substances your body wants to get rid of - such as the remains of medicines, food colors or cholesterol.
    
    A lot of people are reluctant to talk about their bowel movements, which is perfectly natural but Giulia suggests that you should pay attention to the color, shape and consistency of waste, and talk with your doctor regularly to ensure a healthy digestive system.

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