Fiber’s Role in Diet

In this post, I discuss the role of the microbiome and the role of fiber in supporting a healthy microbiome. A healthy microbiome is related to the amount and diversity of the bacteria found within it.

If I had to summarize, I would say this: new research strongly confirms that high fiber diets are healthy diets. Because of this finding, eat 20-200 grams of fiber daily, by eating nuts, berries, whole grains, beans and vegetables.

The Role of the Microbiome
Bacteria in the gut – the “microbiome” – has been the subject of intense research interest over the last decade.

We now know that a healthy microbiome is essential to health and wellbeing.

On a scientific level, we now know that a healthy biome is one with billions of bacteria, of many kinds.

And specifically, we now know that a healthy biome has a layer of mucus along the walls of the intestine.

“The gut is coated with a layer of mucus, atop which sits a carpet of hundreds of species of bacteria, part of the human microbiome.”

If that mucus layer is thick, it is healthy. If it is thin, it is unhealthy (thin mucus layers have been linked to chronic inflammation). (“Their intestines got smaller, and its mucus layer thinner. As a result, bacteria wound up much closer to the intestinal wall, and that encroachment triggered an immune reaction.”)

The Role of Fiber in Supporting a Healthy Microbiome
“Fiber” refers to ruffage from fruits, vegetables, and beans that is hard to digest. If fiber is hard to digest, why are they so universally hailed as “good for you”?

That’s the subject of two newly-reported experiments.

The answer seems to lie in bacteria in the gut – the “microbiome”. Much has been written about their beneficial role in the body. But now it seems that some bacteria in the gut have an additional role: they digest fiber that human enzymes cannot digest.

So some bacteria thrive in the gut because of the fiber they eat. And, in an important natural chain, apparently there are some bacteria in the gut that that thrive because the waste of the bacteria that eats fiber. An ecosystem of bacteria tracing to fiber!

This speaks to one of the most-discussed subjects in science today: how and why is one microbiome populated with relatively few bacteria numbers and types, and why is another microbiome much more diverse – with many more bacteria and bacteria types?

One study, shown below, reports from Tanzania, after reviewing data from tribes that sustain themselves on high fiber foods. The results, reported in Science, clearly show that an ultra-high fiber diet results in ultra high bacteria counts and diversity.

Other findings suggest that fiber is the food of many bacteria types. Because of this, a diverse, healthy bacterial microbiome is dependent on a fiber-rich diet. (“On a low-fiber diet, they found, the population crashed, shrinking tenfold.”)

Indeed, it may well be true that many types of fibers support many types of bacteria.

Proof of this?

Researchers, including Dr. Gerwitz at Georgia State proved that more fiber seems to be better:

Bad: high, fat, low fiber (“On a low-fiber diet, they found, the population crashed, shrinking tenfold.” “Many common species became rare, and rare species became common.“)

Good: modest fiber
Better: high dose fiber (“Despite a high-fat diet, the mice had healthy populations of bacteria in their guts, their intestines were closer to normal, and they put on less weight.”)

Best: high dose of fiber-feeding bacteria
(“Once bacteria are done harvesting the energy in dietary fiber, they cast off the fragments as waste. That waste — in the form of short-chain fatty acids — is absorbed by intestinal cells, which use it as fuel.”

(“Research suggests that when bacteria break down dietary fiber down into short-chain fatty acids, some of them pass into the bloodstream and travel to other organs, where they act as signals to quiet down the immune system.”)

This article documents rich-in-fiber foods:


In recognition of fiber’s benefits, Today’s Dietitian looks at some of the best ways to boost fiber intake,from whole to fortified foods,using data from the USDA National Nutrient Database for Standard Reference.

Top Fiber-Rich Foods
1. Get on the Bran Wagon (Oat bran, All-bran cereal, fiber-one chewy bars, etc)
One simple way to increase fiber intake is to power up on bran. Bran from many grains is very rich in dietary fiber. Oat bran is high in soluble fiber, which has been shown to lower blood cholesterol levels. Wheat, corn, and rice bran are high in insoluble fiber, which helps prevent constipation. Bran can be sprinkled into your favorite foods,from hot cereal and pancakes to muffins and cookies. Many popular high-fiber cereals and bars are also packed with bran.

2. Take a Trip to Bean Town (Limas, Pintos, Lentils, etc)
Beans really are the magical fruit. They are one of the most naturally rich sources of fiber, as well as protein, lysine, vitamins, and minerals, in the plant kingdom. It’s no wonder so many indigenous diets include a bean or two in the mix. Some people experience intestinal gas and discomfort associated with bean intake, so they may be better off slowly introducing beans into their diet. Encourage a variety of beans as an animal protein replacement in stews, side dishes, salads, soups, casseroles, and dips.

3. Go Berry Picking (especially blackberries and raspberries)
Jewel-like berries are in the spotlight due to their antioxidant power, but let’s not forget about their fiber bonus. Berries happen to yield one of the best fiber-per-calorie bargains on the planet. Since berries are packed with tiny seeds, their fiber content is typically higher than that of many fruits. Clients can enjoy berries year-round by making the most of local berries in the summer and eating frozen, preserved, and dried berries during the other seasons. Berries make great toppings for breakfast cereal, yogurt, salads, and desserts.

4. Wholesome Whole Grains (especially barley, oats, brown rice, rye wafers)
One of the easiest ways to up fiber intake is to focus on whole grains. A grain in nature is essentially the entire seed of the plant made up of the bran, germ, and endosperm. Refining the grain removes the germ and the bran; thus, fiber, protein, and other key nutrients are lost. The Whole Grains Council recognizes a variety of grains and defines whole grains or foods made from them as containing “all the essential parts and naturally-occurring nutrients of the entire grain seed. If the grain has been processed, the food product should deliver approximately the same rich balance of nutrients that are found in the original grain seed.â€‌ Have clients choose different whole grains as features in side dishes, pilafs, salads, breads, crackers, snacks, and desserts.

5. Sweet Peas (especially frozen green peas, black eyed peas)
Peas,from fresh green peas to dried peas,are naturally chock full of fiber. In fact, food technologists have been studying pea fiber as a functional food ingredient. Clients can make the most of peas by using fresh or frozen green peas and dried peas in soups, stews, side dishes, casseroles, salads, and dips.

6. Green, the Color of Fiber (Spinach, etc)
Deep green, leafy vegetables are notoriously rich in beta-carotene, vitamins, and minerals, but their fiber content isn’t too shabby either. There are more than 1,000 species of plants with edible leaves, many with similar nutritional attributes, including high-fiber content. While many leafy greens are fabulous tossed in salads, saut ©ing them in olive oil, garlic, lemon, and herbs brings out a rich flavor.

7. Squirrel Away Nuts and Seeds (especially flaxseed and sesame seed)
Go nuts to pack a fiber punch. One ounce of nuts and seeds can provide a hearty contribution to the day’s fiber recommendation, along with a bonus of healthy fats, protein, and phytochemicals. Sprinkling a handful of nuts or seeds over breakfast cereals, yogurt, salads, and desserts is a tasty way to do fiber.

8. Play Squash (especially acorn squash)
Dishing up squash,from summer to winter squash,all year is another way that clients can ratchet up their fiber intake. These nutritious gems are part of the gourd family and contribute a variety of flavors, textures, and colors, as well as fiber, vitamins, minerals, and carotenoids, to the dinner plate. Squash can be turned into soups, stews, side dishes, casseroles, salads, and crudit ©s. Brush squash with olive oil and grill it in the summertime for a healthy, flavorful accompaniment to grilled meats.

9. Brassica or Bust (broccoli, cauliflower, kale, cabbage, and Brussels sprouts)
Brassica vegetables have been studied for their cancer-protective effects associated with high levels of glucosinolates. But these brassy beauties, including broccoli, cauliflower, kale, cabbage, and Brussels sprouts, are also full of fiber. They can be enjoyed in stir-fries, casseroles, soups, and salads and steamed as a side dish.

10. Hot Potatoes
The humble spud, the top vegetable crop in the world, is plump with fiber. Since potatoes are so popular in America, they’re an easy way to help pump up people’s fiber potential. Why stop at Russets? There are numerous potatoes that can provide a rainbow of colors, nutrients, and flavors, and remind clients to eat the skins to reap the greatest fiber rewards. Try adding cooked potatoes with skins to salads, stews, soups, side dishes, stir-fries, and casseroles or simply enjoy baked potatoes more often.

11. Everyday Fruit Basket (especially pears and oranges)
Look no further than everyday fruits to realize your full fiber potential. Many are naturally packed with fiber, as well as other important vitamins and minerals. Maybe the doctor was right when he advised an apple a day, but he could have added pears, oranges, and bananas to the prescription as well. When between fruit seasons, clients can rely on dried fruits to further fortify their diet. Encourage including fruit at breakfast each morning instead of juice; mixing dried fruits into cereals, yogurts, and salads; and reaching for the fruit bowl at snack time. It’s a healthy habit all the way around.

12. Exotic Destinations (especially avocado)
Some of the plants with the highest fiber content in the world may be slightly out of your clients’ comfort zone and, for that matter, time zone. A rainbow of indigenous fruits and vegetables used in cultural food traditions around the globe are very high in fiber. Entice clients to introduce a few new plant foods into their diets to push up the flavor, as well as their fiber, quotient.

13. Fiber Fortification Power
More foods,from juice to yogurt,are including fiber fortification in their ingredient lineup. Such foods may help busy people achieve their fiber goals. As consumer interest in foods with functional benefits, such as digestive health and cardiovascular protection, continues to grow, expect to see an even greater supply of food products promoting fiber content on supermarket shelves.


This article documents the newly-reported experiments:

CREDIT: NYT Article on Fiber Science

Fiber is Good for You. Now we Know Why

By Carl Zimmer
Jan. 1, 2018
A diet of fiber-rich foods, such as fruits and vegetables, reduces the risk of developing diabetes, heart disease and arthritis. Indeed, the evidence for fiber’s benefits extends beyond any particular ailment: Eating more fiber seems to lower people’s mortality rate, whatever the cause.

That’s why experts are always saying how good dietary fiber is for us. But while the benefits are clear, it’s not so clear why fiber is so great. “It’s an easy question to ask and a hard one to really answer,” said Fredrik Bäckhed, a biologist at the University of Gothenburg in Sweden.

He and other scientists are running experiments that are yielding some important new clues about fiber’s role in human health. Their research indicates that fiber doesn’t deliver many of its benefits directly to our bodies.

Instead, the fiber we eat feeds billions of bacteria in our guts. Keeping them happy means our intestines and immune systems remain in good working order.

In order to digest food, we need to bathe it in enzymes that break down its molecules. Those molecular fragments then pass through the gut wall and are absorbed in our intestines.
But our bodies make a limited range of enzymes, so that we cannot break down many of the tough compounds in plants. The term “dietary fiber” refers to those indigestible molecules.

But they are indigestible only to us. The gut is coated with a layer of mucus, atop which sits a carpet of hundreds of species of bacteria, part of the human microbiome. Some of these microbes carry the enzymes needed to break down various kinds of dietary fiber.

The ability of these bacteria to survive on fiber we can’t digest ourselves has led many experts to wonder if the microbes are somehow involved in the benefits of the fruits-and-vegetables diet. Two detailed studies published recently in the journal Cell Host and Microbe provide compelling evidence that the answer is yes.

In one experiment, Andrew T. Gewirtz of Georgia State University and his colleagues put mice on a low-fiber, high-fat diet. By examining fragments of bacterial DNA in the animals’ feces, the scientists were able to estimate the size of the gut bacterial population in each mouse.

On a low-fiber diet, they found, the population crashed, shrinking tenfold.

Dr. Bäckhed and his colleagues carried out a similar experiment, surveying the microbiome in mice as they were switched from fiber-rich food to a low-fiber diet. “It’s basically what you’d get at McDonald’s,” said Dr. Bäckhed said. “A lot of lard, a lot of sugar, and twenty percent protein.”

The scientists focused on the diversity of species that make up the mouse’s gut microbiome. Shifting the animals to a low-fiber diet had a dramatic effect, they found: Many common species became rare, and rare species became common.

Along with changes to the microbiome, both teams also observed rapid changes to the mice themselves. Their intestines got smaller, and its mucus layer thinner. As a result, bacteria wound up much closer to the intestinal wall, and that encroachment triggered an immune reaction.

After a few days on the low-fiber diet, mouse intestines developed chronic inflammation. After a few weeks, Dr. Gewirtz’s team observed that the mice began to change in other ways, putting on fat, for example, and developing higher blood sugar levels.

Dr. Bäckhed and his colleagues also fed another group of rodents the high-fat menu, along with a modest dose of a type of fiber called inulin. The mucus layer in their guts was healthier than in mice that didn’t get fiber, the scientists found, and intestinal bacteria were kept at a safer distance from their intestinal wall.

Dr. Gewirtz and his colleagues gave inulin to their mice as well, but at a much higher dose. The improvements were even more dramatic: Despite a high-fat diet, the mice had healthy populations of bacteria in their guts, their intestines were closer to normal, and they put on less weight.

Dr. Bäckhed and his colleagues ran one more interesting experiment: They spiked water given to mice on a high-fat diet with a species of fiber-feeding bacteria. The addition changed the mice for the better: Even on a high-fat diet, they produced more mucus in their guts, creating a healthy barrier to keep bacteria from the intestinal walls.

One way that fiber benefits health is by giving us, indirectly, another source of food, Dr. Gewirtz said. Once bacteria are done harvesting the energy in dietary fiber, they cast off the fragments as waste. That waste — in the form of short-chain fatty acids — is absorbed by intestinal cells, which use it as fuel.

But the gut’s microbes do more than just make energy. They also send messages. Intestinal cells rely on chemical signals from the bacteria to work properly, Dr. Gewirtz said. The cells respond to the signals by multiplying and making a healthy supply of mucus. They also release bacteria-killing molecules.
By generating these responses, gut bacteria help maintain a peaceful coexistence with the immune system. They rest atop the gut’s mucus layer at a safe distance from the intestinal wall. Any bacteria that wind up too close get wiped out by antimicrobial poisons.

While some species of gut bacteria feed directly on dietary fiber, they probably support other species that feed on their waste. A number of species in this ecosystem — all of it built on fiber — may be talking to our guts.

Going on a low-fiber diet disturbs this peaceful relationship, the new studies suggest. The species that depend on dietary fiber starve, as do the other species that depend on them. Some species may switch to feeding on the host’s own mucus.

With less fuel, intestinal cells grow more slowly. And without a steady stream of chemical signals from bacteria, the cells slow their production of mucus and bacteria-killing poisons.
As a result, bacteria edge closer to the intestinal wall, and the immune system kicks into high gear.

“The gut is always precariously balanced between trying to contain these organisms and not to overreact,” said Eric C. Martens, a microbiologist at the University of Michigan who was not involved in the new studies. “It could be a tipping point between health and disease.”

Inflammation can help fight infections, but if it becomes chronic, it can harm our bodies. Among other things, chronic inflammation may interfere with how the body uses the calories in food, storing more of it as fat rather than burning it for energy.

Justin L. Sonnenburg, a biologist at Stanford University who was not involved in the new studies, said that a low-fiber diet can cause low-level inflammation not only in the gut, but throughout the body.

His research suggests that when bacteria break down dietary fiber down into short-chain fatty acids, some of them pass into the bloodstream and travel to other organs, where they act as signals to quiet down the immune system.

“You can modulate what’s happening in your lung based on what you’re feeding your microbiome in your gut,” Dr. Sonnenburg said.
Hannah D. Holscher, a nutrition scientist at the University of Illinois who was not involved in the new studies, said that the results on mice need to be put to the test in humans. But it’s much harder to run such studies on people.

In her own lab, Dr. Holscher acts as a round-the-clock personal chef. She and her colleagues provide volunteers with all their meals for two weeks. She can then give some of her volunteers an extra source of fiber — such as walnuts — and look for changes in both their microbiome and their levels of inflammation.

Dr. Holscher and other researchers hope that they will learn enough about how fiber influences the microbiome to use it as a way to treat disorders. Lowering inflammation with fiber may also help in the treatment of immune disorders such as inflammatory bowel disease.

Fiber may also help reverse obesity. Last month in the American Journal of Clinical Nutrition, Dr. Holscher and her colleagues reviewed a number of trials in which fiber was used to treat obesity. They found that fiber supplements helped obese people to lose about five pounds, on average.
But for those who want to stay healthy, simply adding one kind of fiber to a typical Western diet won’t be a panacea. Giving mice inulin in the new studies only partly restored them to health.

That’s probably because we depend on a number of different kinds of dietary fiber we get from plants. It’s possible that each type of fiber feeds a particular set of bacteria, which send their own important signals to our bodies.

“It points to the boring thing that we all know but no one does,” Dr. Bäckhed said. “If you eat more green veggies and less fries and sweets, you’ll probably be better off in the long term.”



Is The Secret To A Healthier Microbiome Hidden In The Hadza Diet?

August 24, 20176:11 PM ET
Heard on All Things Considered


Enlarge this image

The words “endangered species” often conjure up images of big exotic creatures. Think elephants, leopards and polar bears.

But there’s another of type of extinction that may be occurring, right now, inside our bodies.

Yes, I’m talking about the microbiome — that collection of bacteria in our intestines that influences everything from metabolism and the immune system to moods and behavior.

For the past few years, scientists around the world have been accumulating evidence that the Western lifestyle is altering our microbiome. Some species of bacteria are even disappearing to undetectable levels.

“Over time we are losing valuable members of our community,” says Justin Sonnenburg, a microbiologist at Stanford University, who has been studying the microbiome for more than a decade.

Now Sonnenburg and his team have evidence for why this microbial die-off is happening — and hints about what we can possibly do to reverse it.

The study, published Thursday in the journal Science, focuses on a group of hunter-gatherers in Tanzania, called Hadza.
Their diet consists almost entirely of food they find in the forest, including wild berries, fiber-rich tubers, honey and wild meat. They basically eat no processed food — or even food that comes from farms.
“They are a very special group of people,” Sonnenburg says. “There are only about 2,200 left and really only about 200 that exclusively adhere to hunting and gathering.”

Sonnenberg and his colleagues analyzed 350 stool samples from Hadza people taken over the course of about a year. They then compared the bacteria found in Hadza with those found in 17 other cultures around the world, including other hunter-gatherer communities in Venezuela and Peru and subsistence farmers in Malawi and Cameroon.

The trend was clear: The further away people’s diets are from a Western diet, the greater the variety of microbes they tend to have in their guts. And that includes bacteria that are missing from American guts.

“So whether it’s people in Africa, Papua New Guinea or South America, communities that live a traditional lifestyle have common gut microbes — ones that we all lack in the industrialized world,” Sonnenburg says.

In a way, the Western diet — low in fiber and high in refined sugars — is basically wiping out species of bacteria from our intestines.

That’s the conclusion Sonnenburg and his team reached after analyzing the Hadza microbiome at one stage of the yearlong study. But when they checked several months later, they uncovered a surprising twist: The composition of the microbiome fluctuated over time, depending on the season and what people were eating. And at one point, the composition started to look surprisingly similar to that of Westerners’ microbiome.

During the dry season, Hadza eat a lot of more meat — kind of like Westerners do. And their microbiome shifted as their diet changed. Some of the bacterial species that had been prevalent disappeared to undetectable levels, similar to what’s been observed in Westerners’ guts.

But then in wet season — when Hadza eat more berries and honey — these missing microbes returned, although the researchers are not really sure what’s in these foods that bring the microbes back.

“I think this finding is really exciting,” says Lawrence David, who studies the microbiome at Duke University. “It suggests the shifts in the microbiome seen in industrialized nations might not be permanent — that they might be reversible by changes in people’s diets.

“The finding supports the idea that the microbiome is plastic, depending on diet,” David adds.

Now the big question is: What’s the key dietary change that could bring the missing microbes back?

Lawrence thinks it could be cutting down on fat. “At a high level, it sounds like that,” he says, “because what changed in the Hadza’s diet was whether or not they were hunting versus foraging for berries or honey,” he says.

But Sonnenburg is placing his bets on another dietary component: fiber — which is a vital food for the microbiome.
“We’re beginning to realize that people who eat more dietary fiber are actually feeding their gut microbiome,”
Sonnenburg says.

Hadza consume a huge amount of fiber because throughout the year, they eat fiber-rich tubers and fruit from baobab trees. These staples give them about 100 to 150 grams of fiber each day. That’s equivalent to the fiber in 50 bowls of Cheerios — and 10 times more than many Americans eat.

“Over the past few years, we’ve come to realize how important this gut community is for our health, and yet we’re eating a low-fiber diet that totally neglects them,” he says. “So we’re essentially starving our microbial selves.”