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What's Fiber Got to Do with It?

We are blessed to live in the 21st century, aren't we? When it comes to food, we live in a land of plenty. Malnutrition is the scourge of far-away countries where drought, economic insecurity & political upheaval are rife, right?

Sadly, today in the US too many Americans live in food deserts with little access to fresh produce, where junk & fast food are staples. This isn't malnutrition from starvation; it's malnutrition from the overconsumption of fattening, nutrient-poor products. Regrettably, both lead to stress, despair, poor health & shortened lifespans.


There is hope. I'd like to give a shout-out to urban farming & ingenious initiatives like teacher Steve Ritz's Bronx Green Machine, Boston's recent startup Fresh Truck, & one couple's humble farm-to-table after-school club at an elementary school in Washington state. These are but a few big-hearted ideas centered around fresh produce that are transforming the health of communities & improving kids' lives in spectacular ways.

America is Sick

Even in wealthy US communities, however, despite ample access to produce, you may be surprised that we suffer from a serious nutrient deficiency: 97% of all Americans are significantly deficient in dietary fiber. On average, we consume daily less than half (15 g) the recommended MINIMUM (32/g) that is deemed necessary to stave off chronic diseases. (1) In 2015 the Dietary Guidelines Advisory Committee flagged fiber as a "nutrient of concern."

Dietary fiber is an assortment of indigestible complex carbohydrates found ONLY in vegetables, fruits, legumes, whole grains, tubers, roots, nuts, seeds, & fungi.

The reason we're so deficient in fiber is that Americans simply don't eat their veggies: 96% of us fail to eat even the MINIMALLY required amounts of leafy greens OR beans; 97% of us fall below short when it comes to orange veggies; & an unbelievable 99% of us don't even hit this low bar when it comes to eating whole grains. (2) We have a nutritional crisis on our hands.

A Long Way to Go

To clarify how far we are from truly healthy fiber intake levels, however, let's look at traditional societies where chronic conditions were virtually nonexistent: Compared to our measly daily 15 g of fiber, rural Chinese consumed 5 times more at 77 g, & rural Africans averaged between 4 to a whopping 8 times more fiber than we, at 60-120 g. (3)

Scientists estimate that our paleolithic forebears consumed more than 100 g of fiber per day, based on observations of modern primitive hunter gatherers & analyses of fossilized human feces. Since fiber is only found in plants, such a fiber-rich diet implies a diet overwhelmingly comprised of plants.(4)

Back to the Future

Evolution is mostly a glacially slow affair. Our teeth, jaws, & digestion have served us for millions of years. However, our diet, especially over the past century, has changed rapidly & beyond recognition.

Our epidemics of obesity, diabetes, heart disease & the rest, may all stem from this mismatch between our basic biology & the foods we currently consume as fuel.

Here's one mechanism, to illustrate:

For millions of years our diet was rich in plant matter, loaded with fiber. We co-evolved with bacteria in our colon that metabolize the fiber we eat to produce short-chain fatty acids. SCFAs activate receptors on the surface of our cells that release hormones, like leptin on fat receptor cells. They, in turn, signal fullness, telling us, "Ok. We're full now; it's time to stop eating."

To our biological selves FOOD = FIBER, because the foods we ate over the long course of our evolution were so chock full of it. So what happens then when we consume a diet void of fiber but heavy in meats, dairy, & refined products? No satiety signalling occurs, telling us we've eaten enough. We continue to eat, consuming more calories than we require. We gain weight. We get fat. (5)

Fiber's not a solo act

Remember, food is a packaged deal. Scientists may isolate nutrients like fiber or protein for closer study, but we eat food, not isolated nutrients.

Just as meat protein is inseparable from the cholesterol, saturated fats & growth hormones in a fish fillet or chicken breast, dietary fiber in eggplant goes hand-in-hand with the vitamins, minerals, phytonutrients & antioxidants also contained therein. All these plant components act in synergy, boosting one another's positive protective effects.

This may be why high-fiber diets, eaten as whole plant foods, succeed on so many fronts, reducing inflammation, quenching oxidative stress, protecting the delicate endothelial lining of our arteries, boosting our gut health.

Bear in mind that there are no short-cuts here. You can't protect yourself by eating an abusive, inflammatory diet & taking a fiber supplement to bail you out. Isolated fiber in processed fiber supplements & powders have not demonstrated the same protective health effects as fiber in whole plants.(6)

Where's the Rub?

While many of fiber's metabolic processes are still not fully understood, we know some of its important protective functions. Fiber:

  • increases the viscosity of foods in the small intestine, slowing glucose absorption, which lowers blood sugar levels & reduces the risk of diabetes

  • eliminates excess estrogen, lowering the incidence of breast cancer

  • flushes out excess cholesterol, protecting our arteries from atherosclerosis

  • speeds transit time in the colon which defends against diverticular diseases & colon cancer.

We have hundreds of studies now, attributing higher fiber consumption to the avoidance of chronic degenerative conditions & conversely, linking diets low in fiber with the onset of many inflammatory, chronic diseases.

Fiber deficiency is associated with a long list of medical risk factors, like hypertension, high blood sugars, hyperlipidemia, diminished lung function (7), & diseases like obesity, diabetes II, metabolic syndrome, cardiovascular disease, stroke, various cancers, diverticular diseases, Crohn's Disease, functional constipation, ulcerative colitis, gallbladder disease, hemorrhoids, kidney stones, & irritable bowel syndrome, & more.

Dreaded infectious diseases like the Zika virus or our local tick-borne diseases notwithstanding, our leading killers today are chronic degenerative diseases. All these maladies & the risk factors that lead up to them are lifestyle driven, caused by a diet centered on inflammatory animal foods, refined processed foods & a sedentary lifestyle.

Every family is touched by these devastating illnesses, now at epidemic levels in the US & rapidly spreading worldwide, & the greatest tragedy of all is that they are entirely preventable. The high fiber content in plant-based foods can help us sidestep this fate & turn the tide.

As you shift your food choices in the direction of plants, increasing your fiber intake as you do, do so gradually at first. You need to allow a little time for gut flora to respond.

A fertile & fascinating area of research in recent years pertains to our gut bacteria. Plant fiber & resistant starch that we can't digest or absorb are essential to our beneficial gut flora colonies. And many of our own metabolic processes, in turn, depend on the health of these bacterial populations.

I'll tell you more about our wondrous microbiome & all it does for us next time.


  2. Krebs-Smith SM1, Guenther PM, Subar AF, Kirkpatrick SI, Dodd KW. Americans do not meet federal dietary recommendations. J Nutr. 2010 Oct; 140(10): 1832–1838.

  3. K M Tuohy, C Gougoulias, Q Shen, G Walton, F Fava, P Ramnani. Studying the human gut microbiota in the trans-omics era--focus on metagenomics and metabonomics. Curr Pharm Des. 2009;15(13):1415-27.

  4. J H Cummings. Topics in Dietary Fiber Research. Gut. 1978 Nov; 19(11): 1087.

  5. M L Sleeth, E L Thompson, H E Ford, S E Zac-Varghese, G Frost. Free fatty acid receptor 2 and nutrient sensing: a proposed role for fibre, fermentable carbohydrates and short-chain fatty acids in appetite regulation. Nutr Res Rev. 2010 Jun;23(1):135-45.

  6. D E Threapleton, D C Greenwood, C E L Evans, C L Cleghorn, and more. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ 2013; 347.

  7. Hanson C., Lyden E, Rennard S, et al. The relationship between dietary fiber intake and lung function in NHANES. Ann Am Thorac Soc. Published online January 19, 2016.

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