The connection between stool and diabetes may not be immediately obvious to everyone. But, in fact, it is not as absurd as it seems. It is not just defensive bacteria that are transplanted with the stool, but an entire microbial organ that plays an important part in regulating the body’s metabolism and immune system. We are still completely ignorant of more than 60 percent of these gut bacteria. Looking for species that may have probiotic effects is time-consuming and difficult, just as the search for medicinal plants was in the past. Only this time, the search is going on inside us. Every day we live and every meal we eat influence the great microbial organ inside us—for better or for worse.
Prebiotics
THE CENTRAL IDEA surrounding the use of prebiotics is to support our good bacteria by eating certain foods. Prebiotics are much more suitable for daily use than probiotics. To gain the benefits they offer, just one condition must be met: good bacteria must already be present in the gut. These can then be encouraged by eating prebiotic food, which gives the good bacteria more power over any bad bacteria that may also be present.
Since bacteria are so much smaller than we are, they view food from a very different perspective from our own. Every little grain becomes a major event, a comet of deliciousness. Food we cannot digest in the small intestine is called dietary fiber or roughage. But, despite the name, it is not rough on the bacteria of the large intestine. Quite the opposite, in fact: they love it! Not all kinds, but some, anyway. Some bacteria love undigested asparagus fibers, while others prefer undigested meat fibers.
Some doctors who recommend their patients eat more dietary fiber do not even really know the reason, which is that they are prescribing a hearty meal for your bacteria that will benefit you, too. Finally your gut microbes get enough to eat, so they can produce vitamins and healthy fatty acids or put the immune system through a good training session. However, there are always some pathogens among the bacteria in our gut. They can use certain foodstuffs to produce substances like indole, phenols, or ammonia. Those are the substances you find in the chemistry cupboard with a warning symbol on the bottle.
This is exactly how prebiotics can help: they are roughage that can only be eaten by nice bacteria. If such a food were available in the human world, the lunch room at work would be quite an eye-opener! Household sugar is not a prebiotic, for example, because it is also a favorite of tooth-decay bacteria. Bad bacteria cannot process prebiotics at all, or hardly, and so they cannot use prebiotics to produce their evil chemicals. At the same time, good bacteria fed with prebiotics grow constantly in power and can gain the upper hand in the gut.
And it is not even very hard to do yourself and your best microbes a favor with prebiotics. Most people already have a favorite prebiotic dish that they would not mind eating more often. My granny always has some potato salad in her fridge, my dad’s specialty is a great endive salad with mandarin segments (here’s a tip: rinse endive leaves briefly under warm water—this leaves them crispy but removes some of the bitterness), and my sister can’t resist asparagus or black salsify in a creamy sauce.
Artichoke, asparagus, endive, green bananas, Jerusalem artichoke, garlic, onion, parsnips, black salsify, wheat (wholegrain), rye, oats, leek.
Those are just a few dishes that Bifidobacteria and Lactobacilli love to eat. We now know that they prefer vegetables from the lily family (Liliaceae), which includes leeks and asparagus, onions, and garlic. They also like Compositae plants, which are those from the sunflower family, including endives, salsify, artichokes, and Jerusalem artichokes. Resistant starches are also on their list of favorites.
Resistant starches form, for example, when potatoes or rice are boiled and then left to cool. This allows the starches to crystalize, making them more resistant to digestion. This means that more of your potato salad or cold sushi rice reaches your microbes untouched. If you don’t already have a favorite prebiotic dish, give them a try. Eating these dishes regularly has an interesting side effect—it causes regular cravings for just such foods.
People who eat mainly low-fiber foods like pasta, white bread, or pizza should not suddenly switch to eating large portions of high-fiber foods. That will only overwhelm their underfed bacterial community. The sudden change will freak the bacteria out, and they will metabolize everything they can in a fit of euphoria. The result is a never-ending trumpet concerto from down below. So, the best strategy is to gradually increase the amount of dietary fiber and not to feed your bacteria with massive, unmanageable amounts. After all, the food we eat is still first and foremost for us, and only secondarily for the inhabitants of our large intestine.
Overproduction of gas is not a pleasant thing—it bloats the gut, making us feel uncomfortable—but passing a bit of wind is not only necessary, it is healthy, too. We are living creatures with a miniature world living inside us, working away and producing many things. Just as we release exhaust fumes into the Earth’s atmosphere, so must our microbes, too. It may make a funny sound and it may smell a bit, but not necessarily. Bifidobacteria and Lactobacilli, for instance, do not produce any unpleasant odors. People who never need to break wind are starving their gut bacteria and are not good hosts for their microbe guests.
Pure prebiotics can be bought at the pharmacy or drugstore. These include the prebiotic inulin, which is extracted from endives, and GOS (galacto-oligosaccharides), which are isolated from milk. These substances have been tested for their health-giving effects and are pretty efficient at feeding only certain Bifidobacteria and Lactobacilli.
Prebiotics are nowhere near as well researched as probiotics, although there are already some sound results pertaining to how they work. Prebiotics promote good bacteria, resulting in a reduction in the amount of toxins produced in the gut. People with liver problems, especially, are unable to detoxify these substances well, and that can cause serious problems. Bacterial toxins have various effects on the body, including anything from fatigue and tremors to comas. When such patients are treated in hospital, they are often given highly concentrated prebiotics, which usually leads to a disappearance of their symptoms.
But bacterial toxins also influence Joe Blow with his fully functioning liver. Toxins can develop, for example, if Joe eats too little dietary fiber and the fiber is all used up at the beginning of his large intestine. The bacteria at the end of his gut will then pounce on any undigested proteins. Bacteria and meat can be a bad combination—we know it’s never a good idea to eat rotten meat. Too many meat toxins can damage the large intestine and, in a worst-case scenario, can even cause cancer. The end of the gut is more prone to cancers on average than the rest of the organ. That’s why researchers are so keen to test how well prebiotics can protect against cancer. Early results are promising.
Prebiotics like GOS are interesting because they are also produced by our own bodies. Ninety percent of the roughage in human breast milk is GOS, and the remaining 10 percent is made up of other indigestible fiber. In cow’s milk, GOS accounts for only 10 percent of the fiber content. So it appears there is something about GOS that is important for human babies. If bottle-fed babies are given formula milk that contains a little GOS powder, their gut bacteria looks similar to that of breastfed babies. Some studies indicate that they are less prone to allergies and neurodermatitis in later life than other bottle-fed babies. GOS has been approved as an additive to infant milk formula for a few years, but it is not obligatory.
Since then, interest in GOS has increased, and another of its effects has now been demonstrated in the laboratory. GOS docks onto gut cells directly—preferably at locations otherwise favored by pathogens. That means these prebiotics act as microscopic shields. Bad bacteria cannot get a good hold and are more likely to slip and fall away. These results have prompted new studies into GOS as a way of preventing traveler’s diarrhea.
More research has been carried out into inulin than GOS. Inulin is sometimes used as a sugar or fat substitute in the food industry because it is a little bit sweet and has a gel-like consistency. M
ost prebiotics are sugars that are linked into chains. When we speak of sugar, we often mean a particular molecule extracted from sugar beet or sugar cane, but there are more than a hundred different kinds of sugar. If, historically, we had developed a sugar industry based on endive sugar, our sweets would not cause tooth decay. Sweetness is not in itself unhealthy, we simply eat only the most unhealthy kind of sweetness.
We are often skeptical about products that are labeled sugar-free or low fat. Sweeteners like aspartame appear to be carcinogenic, and other substances used in typical diet products are also used in factory farming to fatten pigs. So our skepticism is justified. But a product that contains inulin as a sugar or fat substitute may well be healthier than one with a full dose of animal fat or sugar. It is worth reading the label on diet products closely because we can consume some of them with a clean conscience and our gut microbes will thank us for it, too.
Inulin cannot bind with our cells as well as GOS. A large and well-run study in the United Kingdom showed it did not offer any protection against traveler’s diarrhea, although the test subjects did report a general improvement in well-being after taking inulin. This pleasant effect was not reported by members of the control group, who were given a placebo. Inulin can be produced with different chain lengths, which is great for attaining a beneficial distribution of good bacteria. Short inulin chains are eaten by the bacteria at the start of the large intestine and longer chains are consumed closer to the end.
The so-called ITFMIX containing chains of differing lengths has good results, where more surface area equals better results, for example in the absorption of calcium, which requires bacteria to pass it through the gut wall. In one experiment, ITFMIX was seen to improve calcium absorption in young girls by up to 20 percent. That is good for the bones and can help protect against osteoporosis in old age.
Calcium is such a good example because it shows the limits of what can be achieved with prebiotics. Firstly, you have to ingest enough calcium for an effect to kick in, and secondly, prebiotics can do nothing if the problem lies with other organs. When many women go through menopause, their bones get weaker. This is due to a mid-life crisis in the ovaries. They have to say goodbye to their life of producing hormones and learn how to enjoy their retirement. But the bones miss those hormones! No prebiotic in the world can help with this kind of osteoporosis.
Nevertheless, we should not underestimate the power of prebiotics. Almost nothing influences our gut bacteria as much as the food we eat. Prebiotics are the most powerful tool at our disposal if we want to support our good bacteria—that is, those that are already there and are there to stay. Prebiotic creatures of habit, like my potato salad–addicted granny, are doing the best part of their microbial organ a favor without even knowing it. Incidentally, her second favorite vegetable is leeks. Whenever everyone else was ill, she would be there with a big smile and some soup, merrily playing us a few songs on the piano. I don’t know if her defenses had anything to do her microbes, but it’s not an illogical conclusion.
So, we should remember: good bacteria do us good. We should feed them well so they can populate as much of our large intestine as possible. Pasta and bread made of white flour on factory production lines are not enough. We need to include real roughage, made of real dietary fiber in vegetables and fruit. This roughage can also satisfy a sweet tooth and taste delicious. It can be fresh asparagus, sushi rice, or pure, isolated prebiotics from the pharmacy. Our bacteria will like it, and they will thank us with their good services.
SEEN UNDER THE microscope, bacteria look like nothing but little, bright spots against a dark background. But taken together, their sum is much greater than their parts. Each one of us hosts an entire population. Most sit in our mucus membrane, diligently training our immune system, soothing our villi, eating what we don’t need, and producing vitamins for us. Others keep close to the cells of the gut, needling them or producing toxins. If the good and the bad are in equilibrium, the bad ones can make us stronger and the good ones can take care of us and keep us healthy.
(PART FOUR)
UPDATE ON
THE BRAIN-GUT
CONNECTION
WHEN I FIRST sat down in 2013 to write about the brain-gut axis, I spent an entire month staring at a blank screen. At that time, the brain-gut axis was still an extremely new field of research—nearly all the studies carried out until then had been on animals, and so the area was more one of speculation and hypotheses than hard facts. I was determined to include information about the experiments and theories that existed; but, at the same time, I was anxious to avoid raising false hopes or spreading half-truths by jumping the academic gun, so to speak. As I sat sniffling at my sister’s kitchen table one gray Thursday, moaning that I wouldn’t be able to come up with a text that was both accurate and clear enough, she eventually told me, almost as a command, “Put your head down and just write up what you understand of it, and if there’s more or better information in a few years’ time, I’m sure you can add it then.” And that’s exactly what I’ve done.
New Discoveries
DOING ACADEMIC RESEARCH is like walking through unfamiliar territory in the fog. There are few people who would wish to do that every day, happily snapping photos of the new bushes or buildings that emerge from the mist. Sometimes, you can follow a thread for ages, only to find that it is your own sweater that is unraveling. And when that happens, coming home and telling your loved ones what discoveries you’ve made is not quite so cool.
A couple of years ago, we knew that some depressed mice could be cheered up by certain bacteria, and we knew of rats whose character changed completely when other rats’ gut bacteria were transplanted into their bodies, and thus the term “psychobiotics” was coined. It describes microbes that have psychological effects—and which may even be useful in treating conditions like depression. But those animal studies still left us wondering whether such psychobiotics could actually affect humans’ mental health.
There are now some twenty reliable studies of this kind involving human subjects. Three of the bacteria cocktails tested appeared to have no such effect, but all the rest (and this is the more exciting piece of news) do influence the human psyche. Overall, a realistic view of the picture so far is that bacteria don’t cause sudden mood swings; rather, their effect on our emotional state is gradual, often not appearing until three to four weeks after the microbes are administered, and their effect may be fairly limited. Medical thought has also undergone a development when it comes to stress, and the gut has been recognized as playing an important role.
What exactly is going on here, and how strong the effects might be, are still under investigation, with nearly every research team concentrating on different kinds of bacteria.
Mood
FOR RESEARCHERS CONDUCTING experiments into our mood, a stimulating initial question is: what emotions constitute our moods? What are they made up of, so to speak? Most researchers try to answer this with the aid of questionnaires. The many different kinds of questions are categorized according to ranges of feelings: from depressive to cheerful, from fearful to self-assured, from quick-tempered to sweet-tempered, from being concerned (for example, about personal physical well-being) to being positive, and so on.
And that is how a group of English researchers began their first, tentative trials. Lactobacillus casei Shirota (a bacterium you may know from the yogurt drinks available at most supermarkets) improved the disposition of the most ill-tempered third of their test subjects after they had taken it for only three weeks, from “depressive” toward “cheerful.” The subjects with a better general mood saw no further improvement in their spirits, and other feelings, such as anger or anxiety, were not affected to any significant degree.
That was not the case for a study carried out in France. Scientists wanted to investigate a combination of two types of bacteria (Bifidobacterium longum and Lactobacillus helveticus, which are often found in their abbreviated forms, B. longum and L. helveticus, in lists
of ingredients). After four weeks, the test subjects experienced a positive improvement not only in their depressive tendencies, but also in parameters such as anger; or, for example, they showed a propensity to perceive their own physical aches and pains as less severe.
A Dutch team took a more specific approach to the category of mood itself. They were particularly interested in a certain kind of mood: those minor, recurrent, routine lows familiar to everybody, even those of a perfectly healthy mental constitution. Nothing terrible has happened, and we really can’t even pinpoint what’s causing our bad mood—we just feel less perky than usual. Such moments of gloom rarely warrant a mention in our day-to-day conversations or in the media—but they are currently a hot topic among research psychologists. What the researchers are interested in is not the blues themselves, but how we react to them.
This is among the most accurate indicators of whether a healthy person might develop depression or not. Above all, studies have repeatedly shown that the least favorable reaction is fretful brooding—about who might be to blame for our woes, for example.
In this study, the test subjects were asked to spend several minutes imagining themselves in the following situation. It’s definitely not your day today, you don’t feel in top form, but nothing serious has happened to put you in this mood. The subjects then evaluated their own reaction to this mood, according to statements such as the following.
“When I feel that way, I have much less patience and I lose my temper more quickly.”
“When I feel that way, I brood a lot over everything that’s wrong with my life at the moment, or about what my life might have been like if it had taken a different turn.”
Gut: The Inside Story of Our Body's Most Underrated Organ (Revised Edition) Page 21