Fiber: the Epidemic of Absence

1. Feeding the Gut

When you read that fiber “feeds your gut,” that means multiple things, including: 1) food for bacteria (the microbiome) and 2) actual calories for human gut tissue and 3) a bulking agent to prevent bowel stagnation. A healthy diet delivers fiber-derived calories directly to the gut lining, fueling normal neurotransmitter production and the guts three-part protective barrier. Fiber serves a mission-critical role in the normal non-stop communication between the gut ecosystem, your organs, and the brain along the Vagus nerve (below right).

2. Reducing Daily Calorie Intake

Diabetes and weight loss expert, Neal Barnard, MD, reports in his book on reversing diabetes how more fiber in the diet lowers overall caloric intake. Each additional “14 grams of fiber [daily] cuts about 10-percent off your calorie intake.” Barnhard notes how study participants simply feel more full, so they eat less. Researchers observed how increasing fiber by 14 grams daily means a typical eater, say, consuming 2000 calories, will feel full after only eating 1800 calories.  If you are concerned about blood sugar or your hemoglobin-A1c measurement (type-2 diabetes), doctor Barnhard is a widely recognized expert on diabetes reversal. Yes, type-2 diabetes can be entirely reversed!

ABOVE RIGHT — A fruit-harvesting adventure! The whole fiber, nutrients and antioxidants contained in everyday fruits and vegetables lowers inflammation and disease risk. In contrast, diets that habitually rely on highly caloric snacks and meals without whole plants will produce more free radicals — more than the body can handle (oxidative stress).

8. Controlling Reward/Dopamine and Addiction

People understand that sugar and refined carbohydrate foods spike blood glucose.  These also strengthen the brains requirement for dopamine and “reward,” before it feels satisfied. Frequent and routine spikes strengthen of addictive relationship to junk food. The fiber boost — salads and hearty vegetable dishes will lower the curve — the spike –and in time lowers the craving and addictive drive. Reducing the craving with higher fiber meals is reported in Diet, Drugs, and Dopamine (2025) by David A Kessler, M.D., the former director of the U.S. Food and Drug Administration.

9. Fiber-Mediated Neurotransmitter Production

Fiber influences behavioral health through its support of the microbiome. For example, the gut community influences the production of brain messenger chemicals (neurotransmitters).

With a few exceptions[1], the faithful disease-fighters come not from dairy cows, pigs, chickens, or other animal flesh, but from low-calorie, whole, peasant food—the plain-Jane garden-variety vegetables like brassica crops, legumes, fruits and berries, whole grains, mushrooms, nuts and seeds and spices (but not salt). So called “superfoods” can be cheap and close at hand!

Microbiome — 101

The microbes inhabiting your gut are called the microbiome. All together, they might weigh around three pounds soaking wet, depending on diet. Roughly 60-percent of dry-weight poop is dead bacteria.  What do they eat? About 30-percent of the total caloric value of a meal—ideally—will go towards feeding the microbiome. That’s a lot! So when preparing meals, remember, a crowd depends on you!

Specialists and Generalists

Earth’s multi-cellular beings all have interior spaces they share with microbes. It’s been this way for over 1-billion years. The human gut microbiome includes specialists that seem to be found nowhere else, but these are exceptions. Most are generalists and do inhabit other worldly places beyond our gut.[i] Around 1000 unique species are now known to inhabit the lower gastro-intestinal tract (GI tract) of people. On a given day there might be, say, a hundred or more species present. While greater diversity tends to support health, a narrower group of species predominate.

Mutualistic Symbiosis

There certainly is competition between the microbiome species, but when well-cultured on a Real whole food diet, the relationship between you and your microbiome is, in the words of the late Harvard Biologist, E.O Wilson, an example of “mutualistic symbiosis.” Both sides of the relationship are co-dependent beneficiaries.

The fiber that feeds the microbes in the lower small intestine and colon produce useful byproducts used for both your physical and mental wellbeing. There is constant chatter between the gut and the brain and the communication is two-way. In this dialog, the soluble fiber comprised of short chains of sugar—three to ten sugar molecules in length—are solid gold.

Dr. Mayer, the UCLA gastroenterology professor, considers the general health of our gut ecosystem “the gold standard for a healthy diet.”[ii]  Meaning, when your microbiome is healthy, so are you. Diverse, collaborating, and well-fed — the good guys prevail and body and the brain work better.

[i] The Psychobiotic Revolution—pg. 107

[ii] Interconnected Plates, Emeran Mayer, M.D.

Your Guardians and Defenders

 The cells that line the intestine and colon (the epithelium) are powerful guardians and defenders in a very tough neighborhood. Health requires them to be in top shape all the time. They live short, extremely energetic lives of about one week. Narrow folds in this high-energy single layer of cells—what the gut doctors call “crypts”—are among the rare places in the body where stem-cells are common. Any specialized cell that might be in short supply can be created on the spot.

As a university student studying the biological sciences, and as a HS Science teacher, I assumed that all our cells and tissues received their needed energy through the blood stream. Well, mostly that’s true, but now there is a new understanding about the gut.

Rather than receiving all their nutrient through the blood supply, the colon epithelium receives the majority of food energy directly from short-chain fatty acids. Whether we call them resistant starches (amylose) or soluble fiber, smallish soluble fiber chains are crucial to short chain fatty acid production. Fiber literally feeds your gut.

Leaky Gut and Chronic Stress

Chronic gut permeability or “leaking,” introduces pathogens, toxins and allergens directly into the blood and launches a two-stage stress-producing response: 1) the body’s immune and inflammatory system is switched on; 2) and gradually, inflammation triggers our endocrine system (hormones in the brain and elsewhere) which then dials up cortisol, adrenaline, and chronic-anxiety, which appears to translate into elevated rates of depression, bi-polar disorder, ADHD, etc.

Stage 1

In Stage 1, the immune response produces cytokines and chronic systemic inflammation, like a low-grade fever throughout the body. This one doesn’t let up until the gut lining is healed; that is, until the diet changes. During COVID-19 we saw how the immune response itself can cause serious damage, even death, in a metabolically weak patient with a “pre-existing condition.” Inflammation is just the beginning.

The HPA Axis and its proper function defines “you” on any given day: sleep, hunger, satiety, digestion, attention, mood, energy, growth, fat deposition, anxiety, and so forth. The dietary causes of the gut “leaking” includes: nutrient deficient, fatty, and fiber-less meals. The role of stress itself is a complicating factor — a vicious cycle — because stress generates additional high-calorie comfort/reward eating behavior (craving). There are too many calories and the wrong kind.

Related, profound disease factors include insulin resistance and liver fat. The page Insulin and Metabolic Disease outlines a more complete hormonal explanation of chronic stress, but the body’s storage of fat is going terribly wrong. GI tract permeability is a major wrinkle in the U.S. health crisis.

Plants to the rescue! Because gut-cells live energetic short lives, we can quickly stop and reverse gut permeability. Ditching the processed foods and going “plant-forward” can yield dramatic results. However, long-term behavioral health conditions which have links to gut health, such as depression and ADHD, are far more difficult to reprogram.

The image at the top of this page is a far healthier idea. Use a kitchen knife, dehydrator, or wood stove. Sliced and dried, whole fruit is fully preserved, available year-round.

Indeed, the fruit Juice, even though it’s naturally sweet and tastes amazing, is a fantastic source of fructose–which is metabolized 100-percent in the liver. Fructose sans fiber help the body produce liver fat in a comparable manner to “added sugar” (50-percent fructose). More on this subject under Insulin and Metabolic Disease. Also discussed in Carbohydrate Foods and Health.

The upshot: Eat and enjoy whole healthful fruit.

Food and Behavioral Health

Imagine being chronically depressed or having a healthy child whose behavior begins rapidly changing in adolescence and is soon diagnosed with a life-altering behavioral disorder? Behavioral health challenges—like metabolic diseases—are at an all-time high and commonly involve food choice and gut health.

Uma Naidoo, a Harvard Medical School Professor of Psychiatry, specializes in food. She also happens to be professional chef. Food and medications are applied in her clinical practice to treat conditions like ADHD, PTSD, OCD, depression, schizophrenia, insomnia, and other health problems. Her nutritional psychiatric practice and culinary work is based at Massachusetts General Hospital. Let’s look at a few ways food influences mental health, as reported in her 2020 bestseller, This Is Your Brain On Food. Food can heal or harm, and mental health is no exception.

Gluten Intolerance

Gluten is a wheat protein and found in wheat bread and a myriad of wheat-based processed foods. In general, individuals with a mental health diagnosis frequently find help by avoiding gluten. Gluten sensitivity, Irritable Bowel Syndrome, Inflammatory Bowel Disease, celiac disease, general gut health problems and gluten intolerance are higher in those with a behavior health diagnosis.

White Food: Phytonutrient Deficiency

“Brain-based oxidative stress” sounds unhealthy! Mental health challenges are commonly connected to a bland, white, calorie-rich/nutrient-poor diet that generates free radicals like all get-out.

Enter green leafy vegetables, color, fruits and berries, herbs and spices and 8,000-plus polyphenols (still counting). Imagine all the gut-healing friends you gain in one diverse green salad! Lowly lettuce, kale of broccoli — superfoods! Gradually move the person with a behavior health challenge towards colorful, nutrient-rich foods.

Vitamin and Mineral Deficiency

Since three-quarters of the U.S. population doesn’t eat sufficient fruits or vegetables, it’s no wonder we’re having a mental health crisis. Our brain and our “second brain” (the gut) are often missing the well-known nutrients, including the following brain-health factors:

• Vitamins A, C, B1, B6, B12, Folate (B9);
• Minerals Zinc, Iron, Potassium, Magnesium, and Selenium.
• Omega-3 fats

Attention and the Gut

One in twelve Americans are depressed and one in twenty-five have an ADHD diagnosis, an affliction that Dr. Naidoo considers “highly resistant to treatment.” Mental focus and attention require close communication between the pre-frontal cortex (the thinking brain) and the striatum, the brain-segment that deals with addiction and reward behavior. To coordinate that communication well, the brain needs the neurotransmitters like dopamine and noradrenaline—compounds whose building blocks produced by microbes in the gut.

Excessive Sugar and Refined Carbs

Dr. Naidoo finds “a profound correlation” between depression-risk and sugar “flooding the brain with too much glucose.” Refined carbs and sugar elevate pulse-rate, adrenaline, blood-sugar, blood pressure, and insulin. At the same time, it lowers sensitivity to dopamine (addiction and reward). People with a diagnosis of PTSD are twice as likely to develop type-2 diabetes and it is “absolutely clear” that PTSD promotes overeating and obesity, as do anxiety and depression.

Whole plant fiber and food ELIMINATES the blood sugar spikes that lead to obesity, addiction, diabetes and future vascular disease — and they increase our mental wellbeing. Fiber and the healthy microbiome moderate and mediate body and brain stability and facilitate greater well-being.

Fiber is involved in our durable feelings of calm, happiness, and reward. Neurotransmitters like gamma-amino butyric acid (GABA), serotonin, and dopamine, respectively, influence these basic measures of wellbeing. Manufacturing gut-sourced neurotransmitters requires ample dietary fiber.

Fiber-Mediated Neurotransmitter Production

How the amino-acid tryptophan — along with fiber — influences behavioral health illustrates the power of the microbiome to influence behavior. Tryptophan gets used in the formation of several different neurotransmitters (messenger chemicals). These include messengers that signal both happiness and anxiety, respectively serotonin and kynurenine.

• Serotonin, a “happiness molecule,” is mostly produced and stored in specialized cells in the gut lining. Only about 5% of the body’s serotonin is found in the brain or brain-stem. Serotonin’s jobs include regulating mood, quality of sleep, pain sensitivity, gut motility, appetite, and more. Lying in bed in the morning, as you awaken you hear the gurgling. That’s the gut’s nervous system and serotonin triggering gut contraction (peristalsis) and sweeping the remnants of yesterday’s food down into your lower GI tract, and cleaning house.
• Kynurenine is less understood, but is sort of serotonin’s evil twin—a neurotransmitter that when elevated amplifies anxiety signaling (cortisol).

 In Gut-Immune Connection (2021), Dr. Emeran Mayer’s describes research at UCLA. Having ample short-chain fatty acids in the gut means tryptophan is converted to proportionally more serotonin—more happiness and emotional joy—instead of kynurenine, the neurotransmitter that helps elevate cortisol and anxiety. Real food with whole-plant fiber literally keeps the gut-lining healthy, prevents the devastating “leaky gut” scenario, and it stabilizes our mood.

The SAD diet of processed foods and incomplete fiber starves the gut friendlies. In this example, leading to greater anxiety and less happiness. Whole-plant nutrition supports more stable emotions, which means better decision-making. A healthy gut community helps body and brain stay positive and suffer less.