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Katherine Harmon Courage wants us to think of digestion as a collaborative journey between us and our microbes. In his new book, Cultured: How old foods can feed our microbiomeshe considers digestion not as a simple process of feeding, excrement, but as a series of encounters with various microbial actors taking place along the winding tunnel of our digestive tract. Along the way, microbes digest food that we can not and we offer them a warm and well-stocked living space.
But a surge in microbiome research over the past two decades has revealed that they do much more than just digest food. They can promote weight gain, fight infection and even change our mood. Scientists still have a lot to learn about the identity of these microbes, which are important, and how the beneficials exploit their magic.
Incomplete understanding has not stopped the nascent probiotics industry, which argues that we can improve our gut health by taking a pill packed with billions of beneficial bacteria strains, or by eating a yogurt infused with probiotics. It is thought that just eating the right microbes to build a healthier bowel.
Courage thinks that this focus on microbes themselves is myopic. She considers the process of digestion as a collaborative process, because the foods we introduce into our bodies affect the type of bacteria that live in them and grow there. In her book, she explores the science behind how what we feed our microbes affects our health.
She thinks we can learn to work better with our microbial partners looking back. From Greenland to Greece, Courage explores ancient bowel-friendly foods, which are now an integral part of many food crops, and offers suggestions for diversifying the types of foods we feed into our microbiome.
We spoke with Courage about the science behind pro and prebiotics and what she learned to explore fermented staple foods around the world. The interview was modified for brevity and clarity.
The microbiome has drawn a lot of attention to the microbes themselves and what they do for us. You focus a large part of your book on what they eat, the "prebiotics" we give them. Why?
It may be less interesting to talk about fiber than about all the new species that we learn and infuse into food, but what we feed our microbes is just as important as their presence.
I think that, from a human point of view, it is useful to think of microbes in two broad categories. Throughout our lives, we have microbes in our bowels that are adapted to live in them, and there are also microbes that we draw from food or supplements. These are just pbading. They can survive the trip and can certainly offer benefits along the way, but they are not long-term bowel residents, and they will not have the long-term health effects that residents may have. more permanent.
We are beginning to know more about how to create the conditions for resident microbes to grow and possibly benefit us, and that is largely what we give them. And a lot of what we give them is fiber.
What happens if we do not feed the microbes?
So they begin to eat us – our lower gut, which consists of only one thick human cell, which helps us to absorb the digested food as much as possible before expelling it. But it also facilitates the escape of things.
When our microbes do not get enough fiber, they can start destroying the lining that protects this thin layer and sometimes the liner can break, which can literally lead to intestinal leaking syndrome, badociated with many health problems .
When I think of fiber, I think of breakfast cereals transformed into cardboard. Is fiber more diverse than that? What is the importance of having a varied fiber diet to grow a healthy microbiome?
Fiber is any type of carbohydrate that we can not digest and that crosses the digestive system to feed microbes. There are many types of fibers that are broken down by different microbes at different stages of digestion. That's why it makes sense to eat a wide variety of foods and not just focus on one particular supplement here and there. Many types of fiber contribute to the development of many microbes and the creation of different beneficial compounds for us. Which is good because we learn that in general, a more diverse microbiome is an indicator of health. If you look at guts from around the world – and even from the same society – people with more diverse microbiomes tend to be healthier overall.
What are some examples of different types of fiber and the foods that carry them?
Inulin is a type of fiber that is subject to a lot of attention. In fact, we've been adding it to food for longer than we've looked at it, but it's commonly found in foods like chicory root or sunchoke. It's a very long chain of carbohydrates, which means it takes a little more time to cross our system and break down into microbes. Research shows that it encourages the growth of bifidobacteria, lactobacteria [two strains of bacteria commonly badociated with health benefits].
Another big product comes from fruits and vegetables, called fructo-oligosaccharides. It is shorter than inulin and it has been proven that its addition to your diet reduced the markers of inflammation.
Galacto-oligosaccharides are another form of fiber found in milk and are degraded in the colon.
I've been really surprised to learn that resistant starch is another form of fiber. It comes from simpler carbohydrates that have been cooked and then cooled; think of cold potato salad or pasta. So once these starches are crystallized, they become the type of resistant starch that our body can no longer break down [but our microbes can]. Even cold pasta, which you do not necessarily consider to be healthy, can be an excellent source of resistant starch.
Are any other aspects of our diet that fibers affect the microbiome?
Almost everything we eat has an impact on our microbes. An example I'm talking about in the book is meat. A kind of fat meat such as pork can have a negative impact on health through our microbes because it produces a metabolite called TMAO, badociated with adverse health effects. But fish oil has proven beneficial – microbes from mice fed on fish oil instead of pork lard have produced far less TMAO.
Another exciting area of research is that of knowing how gene expression in the same microbial strains can change, depending on what they are feeding. Different metabolites are not produced by different microbes, but by the same microbes fed differently.
You've looked at a lot of research comparing western diets to more traditional hunter-gatherer diets. How are their diets and microbiomes different?
Researchers are turning to hunter-gatherer societies to try to understand what our ancestral regimes looked like before the advent of agriculture. This can give us clues about the types of diets for which humans are adapted.
These studies show that we eat a lot less fiber than in the past.
The FDA recommends something like 30 grams of fiber a day, but most Americans do not even get it. Traditional hunter-gatherer crops, such as the Hadza group in Africa, consume more than 100 grams of fiber per day.
So, modern Western diets consume 15 to 30 grams of fiber a day, which allows our body to adapt to more than 100. This lack of fiber seems to have a considerable impact on the diversity of our microbiome. These traditional fiber-rich diets have a much more diverse microbiome than [people eating] more modern diets, [and the former] is often linked to better health outcomes. It's hard to draw hard conclusions about the causes and effects here because many other factors affect lifestyle, but it does seem that our low-fiber diet is not good for your health.
By reporting your book, you go on a culinary quest in search of all these fermented and microbial foods. What is the most amazing food you have encountered?
By far, it was Kiviak, a traditional Inuit food from Greenland. Kiviak is a bird, especially an auk, fermented in a seal skin. So when the auks are in season, they capture the birds and other objects [up to 500] in seal skin, sew it and let it ferment underground for a year, then detach it and eat it.
It is important to remember that fermentation did not necessarily occur because people thought about the health benefits. It was a way of preserving food and going through a harsh winter in Greenland.
Many of these foods are not considered individual things to consume for a specific benefit, but as rich and essential elements of food culture. How does culture determine how we feed our microbiome?
There is not really a culture that does not include some kind of fermented food, and many have a rich diversity of different types of fermented food.
We think kimchi is Korean fermented food and it's their national food, but they have so many other types of fermented foods that they infuse throughout the kitchen.
These foods are not really considered a separate thing. You do not eat kimchi as a healthy snack for your germs, then return to your normal diet. These fermented foods are incorporated into the food culture – they are condiments, accompaniments, aromas. A meal seems incomplete or unbalanced without them.
And is this type of consistency a healthier and more sustainable way to feed our microbiome?
Yes. Generally, types of fermented wild foods, such as kimchi, sauerkraut and pickles, tend to present a greater diversity of microbes than your store-bought yogurts, infused with probiotics. We still do not know if each strain of these foods is good for us, but again, greater diversity tends to be badociated with better health.
What advice would you give to those who wish to improve the health of their microbiome?
It's really about creating the right environment for our native microbes, and the best way to do that is to eat many types of fiber. I do not think probiotics or looking for specific fermented foods are bad, of course, but focusing on fiber is a good first step.
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