FIBER: FEEDING THE ECOSYSTEM FOR THRIVING HEALTH
We hear regularly that fiber is good for us. We know we’re supposed to eat fruits and vegetables, and at our yearly physicals, we’re encouraged to eat more of it by our doctor. Fiber is one of those words that feels familiar, and truthfully, rather boring. But the pathway behind fiber’s health-promoting mechanism is a fascinating and symbiotic event between our cells and the billions of microorganisms that live within us. For decades we’ve known that fiber is good for us, but the story of why and how it is so health-promoting has only recently begun to unfold. Understanding this tale is essential to prioritizing and enjoying its benefits.
What is Fiber?
When we consume food, it’s energy is not immediately available to us. To understand the path that nourishment must travel, it’s important to first consider the nature of how we acquire energy. Our gastrointestinal tract is a long funnel that stretches from our sinuses and mouth all the way through the colon. Think of it as a pathway where the outside world tunnels through us. It is actually not the “inside” of our bodies. It’s a barrier between us and the outside world. This tract is lined with a thin sheet of epithelial cells which is then covered in protective mucus. On top of the protective layer is where billions of microorganisms are housed — collectively, this ecosystem is our microbiome. The microbial population ideally consists of many species of bacteria, fungi, yeasts, and other tiny organisms that benefit our health.
The GI tract also houses the majority of the human immune system. The delicate balance of well-maintained epithelial cells, a friendly microbial population, and in-tact mucus layers leads to healthy immune behavior. When one part of this ecosystem is depleted, such as the mucous layer or the tissue lining the tract, the microbial populations can encroach too closely across the barrier and an inflammatory response is triggered.
Each compartment of the GI has specific adaptations and functions. Particular enzymes or molecules are secreted in certain areas where they are needed to perform a given task in order to assist the phases of nutrient processing. The mouth secretes a small amount of certain digestive enzymes, particularly amylases to digest starch; the stomach secretes hydrochloric acid to create an extremely low pH that can denature or cleave proteins and kill pathogens; and the small intestine is where the majority of nutrient absorption appears to occur. But humans cannot simply absorb somewhat digested nutrients. We only have enzymes that can break certain bonds, and we only can absorb the smallest units of each macromolecule. There are many structures that we cannot cleave into units small enough for this retention. That is where the symbiotic nature of our microbial populations enter the digestive pathway.
Bacteria can cleave bonds in plants that we cannot, and thus they can liberate nutrients for us to access and also feed themselves in the process. Fiber contains the indigestible molecules whose bonds we cannot break on our own. Soluble fibers are water-soluble and create a gel-like substance as they breakdown and then pass through the colon, and insoluble fibers are not water-soluble and remain solid as they are processed. Both are found in plants that humans consume.
Fiber and Health
Recent studies comparing low-fiber diets to high-fiber diets have explored possible mechanisms for the balance of this ecosystem. Low-fiber diets in mice have been shown to dramatically deplete their microbiota and correlate with changes in what species are present in their gut. This crash in the population then coincided with a thinning of the mucus barrier and an inflammatory immune response (Zou et al., 2017).
Unfortunately, the diet tested mimicked what the majority of Americans continue to eat — nutrition that’s high in sugar, high in lard, and low in fiber. The mice that were kept on this diet eventually suffered from chronic inflammation, fat gain, and higher blood sugar levels. The lack of microbial diversity and the thinning of protective mucus was associated with sustained inflammation that resulted in poor health.
The causal pathway for the immune response is thought to be a multi-step breakdown. First, the lack of fiber starves the microorganisms in the GI. This starvation leads to population decreases, and thus reduces the molecules that some species produce that help strengthen the mucus barrier. The barrier also might be consumed by some microorganisms as they try to cope with the lack of fuel. As this protective layer thins, the bacterial population encroaches on human tissue too closely, and an inflammatory response is initiated by immune cells that are prompted to defend this threat. Living in that precarious chronic state then leads to the negative health outcomes associated with sustained inflammation — fat gain, metabolic disturbances, and poor immune health.
Fiber and Microbial Diversity
One possible cause precipitous to the inflammation is a term that researchers are calling “colony atrophy.” A lack of diversity in the speciation of the microbiome is correlated with dysregulated mucus production and epithelial function and thus increased immune activity.
The good news is that a diet high in fiber is correlated with increased microbial diversity and balanced immune function. In some studies, added fiber was shown to be protective even when the subject was still eating a processed food diet. When bacteria feed on plant fibers that humans cannot digest, they produce a substance known as short-chain fatty acids (SCFAs), which intestinal cells can then use as fuel to produce mucus, receive messages, and kill pathogens.
Some bacteria feed directly on dietary fibers, and other species may be feeding on the waste that fiber-consuming bacteria produce. Either way, the fuel is allowing microorganisms to flourish and diversify. But all of this ecosystem is dependent on the steady income of plant fibers.
Fiber and Aging
Interestingly, a more recent review of a major national health data set revealed a benefit of fiber that had not been elucidated before: fiber affects biological aging.
Telomeres are tiny caps on the ends of chromosomes that work to protect genetic material. As humans age, telomeres shorten; making it a proxy for estimating the rate of biological aging in an organism. After examining data from 5,674 U.S. adults in the National Health and Nutrition Examination Survey (NHANES), researchers discovered that telomere length was correlated with how many grams of fiber were consumed daily by the individual. Specifically, for each 1 g increment in fiber intake per 1000 kcal, telomeres were 8.3 base pairs longer. Because each additional year of chronological age was associated with telomeres that were 15.5 base pairs shorter, these results suggest that a 10 g increase in fiber intake per 1000 kcal would correspond with telomeres that are 83 base pairs longer. On average, this would equate to 5.4 fewer years of biologic aging. When smoking, BMI, alcohol use and physical activity were adjusted for, each 10 g increment in fiber accounted for telomeres that were 67 base pairs longer, resulting in a biologic aging difference of about 4.3 years (Tucker, 2018).
This means that the human body may age more slowly and remain biologically younger as the daily dose of fiber increases. The suggested mechanisms for this relationship are complex but include the inflammatory response concepts previously mentioned, as well as other immune-modulating effects and mediation of oxidative stressors.
Unfortunately, U.S. adults continue to have very low fiber intake on average, with recent studies showing them as consuming less than one-half of the recommended amounts daily (Tucker 2018). Given that our microbiome and immune health appear to have a dose-dependent response to dietary fiber, it’s clear that this is a component of obesity and disease in the U.S. — where metabolic illnesses continue to be a top public health crisis.
Your Daily Doses of Fiber
One of the encouraging things about fiber issues is that its a relatively simple problem to fix — a person needs to eat more of it. Yet, this is challenging to actually implement in our current food culture. Thankfully, you can change this in your home, on your plate, right now.
Whole, real foods need to be consumed at breakfast, lunch, snacks, and dinner. All meals should contain a portion of whole plant foods. The daily recommended amounts of fiber are 30 or more grams for men and 25 or more grams for women. If you want to investigate and see how many grams you’re getting daily, you can track your meals in a nutrient-tracking app such as Cronometer. Otherwise, its simple to first start by making half your plate consist of fresh color at mealtimes. Vegetables of all kinds (including frozen), fruits, seeds, nuts, potatoes, legumes, and beans are all wonderful sources of dietary fiber and resistant starch. All of these can be used to make delicious meals throughout the year. The key is to prioritize, value, and learn to enjoy these powerful foods.
| Fiber type | Found in |
| Beta-glucans | Baker’s yeast, some mushrooms, some grains, seaweed |
| Cellulose / hemicellulose | Plant cell walls, especially plants with a rigid structure (e.g. trees) |
| Chitin | Fungi, exoskeletons (e.g. crab shells) |
| Chitosan | Produced as a chitin derivative |
| Fructans | Many vegetables and grains, such as chicory, Jerusalem artichoke, barley, and the Allium group (onions, leeks, garlic, etc.) |
| Gums | Seaweeds, barley bran, some tree saps and seeds |
| Lignins | Plant cell walls, especially xylem (nutrient-transporting) cells |
| Non-digestible dextrins | Plant starches |
| Non-digestible oligosaccharides (the prebiotic fibers) like inulin, fructo- and galacto-oligosaccharides | For inulin and fructo-oligosaccharide, see fructans. Galacto-oligosaccharides are derived from lactose in milk. |
| Pectin | Fruits such as apples, apricots, quince, guava, and citrus. Citrus peels are a very high source of pectin (30% of weight). |
| Polydextrose | Synthesized from dextrose (combined with citric acid and sorbitol), used as a starch replacer in commercial food products |
| Resistant starches | Seeds, legumes, whole grains, potato, corn, green bananas (especially if these foods are cooked then cooled) |
-Precision Nutrition
Not only are many of these foods super delicious and easy to incorporate, but they have benefits beyond their colorful nutrients. The fiber can assist with weight loss and healthy weight maintenance, GI health, colonic transit, lowering cholesterol, increasing microbial diversity, feeling fuller longer, cancer protection, cardiovascular protection, and even increased energy expenditure.
Those who can make this lifestyle change stand to reap wonderful benefits. These foods are the items that we’re designed to consume. If we look at the framework of the relationship between the microorganisms that we house and the symbiotic benefits our cells acquire from their presence, it’s clear that we are designed to work with, feed, and benefit from billions of microbiota all around our bodies. The health, diversity, and balance of that ecology is nothing short of essential to achieving thriving human health.
FIBER: FEEDING THE ECOSYSTEM FOR THRIVING HEALTH
We hear regularly that fiber is good for us. We know we’re supposed to eat fruits and vegetables, and at our yearly physicals, we’re encouraged to eat more of it by our doctor. Fiber is one of those words that feels familiar, and truthfully, rather boring. But the pathway behind fiber’s health-promoting mechanism is a fascinating and symbiotic event between our cells and the billions of microorganisms that live within us. For decades we’ve known that fiber is good for us, but the story of why and how it is so health-promoting has only recently begun to unfold. Understanding this tale is essential to prioritizing and enjoying its benefits.
What is Fiber?
When we consume food, it’s energy is not immediately available to us. To understand the path that nourishment must travel, it’s important to first consider the nature of how we acquire energy. Our gastrointestinal tract is a long funnel that stretches from our sinuses and mouth all the way through the colon. Think of it as a pathway where the outside world tunnels through us. It is actually not the “inside” of our bodies. It’s a barrier between us and the outside world. This tract is lined with a thin sheet of epithelial cells which is then covered in protective mucus. On top of the protective layer is where billions of microorganisms are housed — collectively, this ecosystem is our microbiome. The microbial population ideally consists of many species of bacteria, fungi, yeasts, and other tiny organisms that benefit our health.
The GI tract also houses the majority of the human immune system. The delicate balance of well-maintained epithelial cells, a friendly microbial population, and in-tact mucus layers leads to healthy immune behavior. When one part of this ecosystem is depleted, such as the mucous layer or the tissue lining the tract, the microbial populations can encroach too closely across the barrier and an inflammatory response is triggered.
Each compartment of the GI has specific adaptations and functions. Particular enzymes or molecules are secreted in certain areas where they are needed to perform a given task in order to assist the phases of nutrient processing. The mouth secretes a small amount of certain digestive enzymes, particularly amylases to digest starch; the stomach secretes hydrochloric acid to create an extremely low pH that can denature or cleave proteins and kill pathogens; and the small intestine is where the majority of nutrient absorption appears to occur. But humans cannot simply absorb somewhat digested nutrients. We only have enzymes that can break certain bonds, and we only can absorb the smallest units of each macromolecule. There are many structures that we cannot cleave into units small enough for this retention. That is where the symbiotic nature of our microbial populations enter the digestive pathway.
Bacteria can cleave bonds in plants that we cannot, and thus they can liberate nutrients for us to access and also feed themselves in the process. Fiber contains the indigestible molecules whose bonds we cannot break on our own. Soluble fibers are water-soluble and create a gel-like substance as they breakdown and then pass through the colon, and insoluble fibers are not water-soluble and remain solid as they are processed. Both are found in plants that humans consume.
Fiber and Health
Recent studies comparing low-fiber diets to high-fiber diets have explored possible mechanisms for the balance of this ecosystem. Low-fiber diets in mice have been shown to dramatically deplete their microbiota and correlate with changes in what species are present in their gut. This crash in the population then coincided with a thinning of the mucus barrier and an inflammatory immune response (Zou et al., 2017).
Unfortunately, the diet tested mimicked what the majority of Americans continue to eat — nutrition that’s high in sugar, high in lard, and low in fiber. The mice that were kept on this diet eventually suffered from chronic inflammation, fat gain, and higher blood sugar levels. The lack of microbial diversity and the thinning of protective mucus was associated with sustained inflammation that resulted in poor health.
The causal pathway for the immune response is thought to be a multi-step breakdown. First, the lack of fiber starves the microorganisms in the GI. This starvation leads to population decreases, and thus reduces the molecules that some species produce that help strengthen the mucus barrier. The barrier also might be consumed by some microorganisms as they try to cope with the lack of fuel. As this protective layer thins, the bacterial population encroaches on human tissue too closely, and an inflammatory response is initiated by immune cells that are prompted to defend this threat. Living in that precarious chronic state then leads to the negative health outcomes associated with sustained inflammation — fat gain, metabolic disturbances, and poor immune health.
Fiber and Microbial Diversity
One possible cause precipitous to the inflammation is a term that researchers are calling “colony atrophy.” A lack of diversity in the speciation of the microbiome is correlated with dysregulated mucus production and epithelial function and thus increased immune activity.
The good news is that a diet high in fiber is correlated with increased microbial diversity and balanced immune function. In some studies, added fiber was shown to be protective even when the subject was still eating a processed food diet. When bacteria feed on plant fibers that humans cannot digest, they produce a substance known as short-chain fatty acids (SCFAs), which intestinal cells can then use as fuel to produce mucus, receive messages, and kill pathogens.
Some bacteria feed directly on dietary fibers, and other species may be feeding on the waste that fiber-consuming bacteria produce. Either way, the fuel is allowing microorganisms to flourish and diversify. But all of this ecosystem is dependent on the steady income of plant fibers.
Fiber and Aging
Interestingly, a more recent review of a major national health data set revealed a benefit of fiber that had not been elucidated before: fiber affects biological aging.
Telomeres are tiny caps on the ends of chromosomes that work to protect genetic material. As humans age, telomeres shorten; making it a proxy for estimating the rate of biological aging in an organism. After examining data from 5,674 U.S. adults in the National Health and Nutrition Examination Survey (NHANES), researchers discovered that telomere length was correlated with how many grams of fiber were consumed daily by the individual. Specifically, for each 1 g increment in fiber intake per 1000 kcal, telomeres were 8.3 base pairs longer. Because each additional year of chronological age was associated with telomeres that were 15.5 base pairs shorter, these results suggest that a 10 g increase in fiber intake per 1000 kcal would correspond with telomeres that are 83 base pairs longer. On average, this would equate to 5.4 fewer years of biologic aging. When smoking, BMI, alcohol use and physical activity were adjusted for, each 10 g increment in fiber accounted for telomeres that were 67 base pairs longer, resulting in a biologic aging difference of about 4.3 years (Tucker, 2018).
This means that the human body may age more slowly and remain biologically younger as the daily dose of fiber increases. The suggested mechanisms for this relationship are complex but include the inflammatory response concepts previously mentioned, as well as other immune-modulating effects and mediation of oxidative stressors.
Unfortunately, U.S. adults continue to have very low fiber intake on average, with recent studies showing them as consuming less than one-half of the recommended amounts daily (Tucker 2018). Given that our microbiome and immune health appear to have a dose-dependent response to dietary fiber, it’s clear that this is a component of obesity and disease in the U.S. — where metabolic illnesses continue to be a top public health crisis.
Your Daily Doses of Fiber
One of the encouraging things about fiber issues is that its a relatively simple problem to fix — a person needs to eat more of it. Yet, this is challenging to actually implement in our current food culture. Thankfully, you can change this in your home, on your plate, right now.
Whole, real foods need to be consumed at breakfast, lunch, snacks, and dinner. All meals should contain a portion of whole plant foods. The daily recommended amounts of fiber are 30 or more grams for men and 25 or more grams for women. If you want to investigate and see how many grams you’re getting daily, you can track your meals in a nutrient-tracking app such as Cronometer. Otherwise, its simple to first start by making half your plate consist of fresh color at mealtimes. Vegetables of all kinds (including frozen), fruits, seeds, nuts, potatoes, legumes, and beans are all wonderful sources of dietary fiber and resistant starch. All of these can be used to make delicious meals throughout the year. The key is to prioritize, value, and learn to enjoy these powerful foods.
| Fiber type | Found in |
| Beta-glucans | Baker’s yeast, some mushrooms, some grains, seaweed |
| Cellulose / hemicellulose | Plant cell walls, especially plants with a rigid structure (e.g. trees) |
| Chitin | Fungi, exoskeletons (e.g. crab shells) |
| Chitosan | Produced as a chitin derivative |
| Fructans | Many vegetables and grains, such as chicory, Jerusalem artichoke, barley, and the Allium group (onions, leeks, garlic, etc.) |
| Gums | Seaweeds, barley bran, some tree saps and seeds |
| Lignins | Plant cell walls, especially xylem (nutrient-transporting) cells |
| Non-digestible dextrins | Plant starches |
| Non-digestible oligosaccharides (the prebiotic fibers) like inulin, fructo- and galacto-oligosaccharides | For inulin and fructo-oligosaccharide, see fructans. Galacto-oligosaccharides are derived from lactose in milk. |
| Pectin | Fruits such as apples, apricots, quince, guava, and citrus. Citrus peels are a very high source of pectin (30% of weight). |
| Polydextrose | Synthesized from dextrose (combined with citric acid and sorbitol), used as a starch replacer in commercial food products |
| Resistant starches | Seeds, legumes, whole grains, potato, corn, green bananas (especially if these foods are cooked then cooled) |
-Precision Nutrition
Not only are many of these foods super delicious and easy to incorporate, but they have benefits beyond their colorful nutrients. The fiber can assist with weight loss and healthy weight maintenance, GI health, colonic transit, lowering cholesterol, increasing microbial diversity, feeling fuller longer, cancer protection, cardiovascular protection, and even increased energy expenditure.
Those who can make this lifestyle change stand to reap wonderful benefits. These foods are the items that we’re designed to consume. If we look at the framework of the relationship between the microorganisms that we house and the symbiotic benefits our cells acquire from their presence, it’s clear that we are designed to work with, feed, and benefit from billions of microbiota all around our bodies. The health, diversity, and balance of that ecology is nothing short of essential to achieving thriving human health.