Have you ever wondered if there’s a natural way to lower your high blood pressure, guard against Alzheimer's, lose weight, and feel better? Well as it turns out there is. Michael Greger, M.D. FACLM, founder of NutritionFacts.org, and author of the instant New York Times bestseller “How Not to Die” celebrates evidence-based nutrition to add years to our life and life to our years.

Fabulous Fiber

Why is fiber so important, and are you getting enough?

This episode features audio from The Five to One Fiber Rule, Is the Fiber Theory Wrong?, and Does Fiber Really Prevent Diverticulosis?. Visit the video pages for all sources and doctor’s notes related to this podcast.


Welcome to the Nutrition Facts podcast.  I’m your host Dr. Michael Greger.  I am thrilled that you have decided to join me today.  Because the more I learn about latest nutrition research – the more convinced I am that this information can make a real difference in all of our lives.  And I like nothing better – than sharing it with you. 

Today we take a close look at fiber – that fabulous stuff that helps decrease our cancer risk, lowers our risk of colitis, crohn’s disease, appendicitis, constipation.  It’s something we need to get enough of on a daily basis.  So why don’t we eat enough of it? 

In our first story, we share some guidelines on how to read food labels for grain products such as bread and breakfast cereals.

When people think fiber, they think constipation. And it’s true, if we could get Americans to just eat the minimum recommended daily intake of fiber-containing foods, we could save our country 80 billion dollars —and that’s just from the effects on constipation alone. Accumulating evidence indicates that greater dietary fiber intake reduces risk for diabetes, heart disease, certain cancers, weight gain, obesity, and diverticular disease, as well as constipation. So, we need to eat more fiber rich foods, which means eating more whole grains, vegetables, fruits, and legumes (beans, split peas, chickpeas and lentils).

As fiber intake goes up, the risk of metabolic syndrome appears to go down: less inflammation and an apparent step-wise drop in obesity risk.

And so, no surprise, perhaps, that greater dietary fiber intake is associated with a lower risk of heart disease. A 9% lower risk for every additional 7 g/day of total fiber consumed. That’s just like some rice and beans or a few servings of fruits and vegetables.

How does fiber do its magic? What are the mechanisms by which dietary fiber may extend our lifespan? It helps get rid of excess bile, feeds our good bacteria, changes our gut hormones, which collectively helps control our cholesterol, and body weight, blood sugar, and blood pressure, which reduces the risk for cardiovascular disease. Reducing inflammation is a whole ‘nother mechanism by which fiber may help prevent chronic disease.

The accompanying editorial to the fiber and heart disease meta-analysis implored doctors to enthusiastically and skillfully recommend that patients consume more dietary fiber. That means a lot of whole plant foods. If, however,  we do buy something packaged, the first word in the ingredients list should be “whole,” but then, the rest of the ingredients could be junk; so, a second strategy is to look at the ratio of grams of carbohydrates to grams of dietary fiber. We’re looking for about five to one or less. So, for example, whole wheat Wonder Bread passes the first test: first word is whole, but then it’s like corn syrup and a chemistry set. Let’s see if it passes the five to one rule? What you do is divide the carbohydrates by the dietary fiber. 20 divided by 2.7 is about 7, that’s more than five, so goes back on the shelf. Better than white, though, which clocks in at over 18. Here’s one that makes the cut. 15 divided by three equals five.

You can do the same thing with breakfast cereal. Multi-Grain Cheerios. Sounds healthy, but has a ratio over 7. And then, it just goes downhill from there.

The editorial concluded, the recommendation to consume diets with adequate amounts of dietary fiber may turn out to be the most important nutritional recommendation of all.

In our next story we explore why the extraordinarily low rates of chronic disease among plant-based populations have been attributed to fiber, but reductionist thinking may lead us astray.

Fiber-containing foods may not only help prevent heart disease, but help treat it as well. Heart patients who increase their intake of fiber after their first heart attack reduce their risk of a second and live longer than those that don’t. But what if we really don’t want to have a heart attack in the first place? If seven grams of fiber gets us a 9% reduced risk, would 77 grams a day drop our risk 99%? Well, that’s what they used to eat in Uganda, a country in which coronary heart disease, our #1 killer, was almost non-existent.

Heart disease was so rare among those eating these traditional plant-based diets, there were papers published like this: “A case of coronary heart disease in an African.” After 26 years of medical practice, they finally recorded their first case of coronary heart disease in a judge consuming a partially Westernized diet, having fiber-free foods like meat, dairy, and eggs displace some of the plant foods in his diet.

Were there so few cases because Africans didn’t live very long? No, the overall life expectancy was low because of diseases of childhood, like infections, but when they reached middle age, they had the best survival, thanks in part to our number one killer being virtually absent. Of course, now, diets have Westernized across the continent, and it gets to now be their #1 killer as well. From virtually non-existent to an epidemic.

Some blame this change on too much animal fat; others blame it on too little fiber, but they both point to the same solution, a diet centered around unrefined plant foods. In fact, sometimes, it’s easier to convince patients to improve their diets by eating more of the good foods to kind of crowd out some of the less healthy options.

The ‘dietary fiber hypothesis,’ first proposed in the 70’s, zeroed in on fiber as the dietary component that was so protective against chronic disease. And since then, evidence has certainly accumulated that those who eat lots of fiber appear protected from several chronic conditions, but maybe fiber is just a marker for the consumption of foods as grown, whole unprocessed plant foods, the only major source of fiber. So, maybe all these studies showing fiber is good are really just showing that eating lots of unrefined plant foods are good.

Fiber is but one component of plant foods, and to neglect the other components—like all the phytonutrients—is to seriously limit our understanding.

Why did Drs. Burkitt, Trowell, Painter, and Walker—the fathers of the fiber theory—place all their bets on fiber? One possible explanation for this is that they were doctors, and we doctors like to think in terms of magic bullets. That’s how we’re trained—there’s one pill, one operation. They were clinicians, not nutritionists, and so they developed a reductionist approach. The problem with that approach is that if we reach the wrong conclusion, we may come up with the wrong solution. Burkitt saw disease rates 

skyrocket after populations went from eating whole plant foods to refined plant and animal foods, but instead of telling people that we should go back to eating whole plant foods, he was so convinced fiber was the magic component, his top recommendation was to eat whole grain bread—but they never used to eat any kind of bread in Uganda— and sprinkling some spoonfuls of wheat bran on your food.

But studies to this day associating high fiber intake with lower risk of disease and death relate only to fiber from food intake rather than from fiber isolates or extracts. It is not at all clear whether fiber consumed as a supplement is beneficial.

In retrospect, maybe it was a mistake to isolate fiber from the overall field of plant food nutrition. The evidence supporting the value of fruits, vegetables, and whole grains, as opposed to only fiber, has proved to be much more consistent. Whole plant foods are of fundamental importance in our diet. Fiber is just one of the many beneficial components of fruits, vegetables, nuts, grains, and beans. Much of the effort on defining fiber and studying the fiber isolate would have been better applied to a whole-plant-food approach.

Finally, the parable of the tiny parachute explains the study that found no relationship between dietary fiber intake and diverticulosis.

A study out of the University of North Carolina found no association between dietary fiber intake and diverticulosis in comparing the group that ate the highest amount, 25 grams—three times the amount of the lowest fiber intake group. They concluded that a low-fiber diet was not associated with diverticulosis. The university sent out a press release: “Diets high in fiber won’t protect against diverticulosis.” The press picked it up. Study finds high-fiber diet may not protect against diverticulosis. Went all over the paleo blogs, and even medical journals; an important paper calling into question the fiber theory of the development of diverticulosis. Other editorials, though, caught the critical flaw. To understand this, let’s turn to another dietary deficiency disease: scurvy.

Medical experiments on prisoners at the Iowa State Penitentiary showed that clinical signs of scurvy start appearing after just 29 days without vitamin C. Experiments on pacifists during World War II showed the same thing—that it takes about 10mg of vitamin C a day to prevent scurvy. So, imagine going back in time a few centuries, when they were still trying to figure scurvy out. Dr. James Linde had this radical theory that citrus fruits could cure scurvy. What if an experiment were designed to test this crazy theory, in which sailors were given the juice of either one wedge of lemon, or three wedges of lemons a day? The printing press pamphleteers would all be touting the study that found that a low-vitamin C diet is not associated with scurvy.

See, a wedge of lemon only yields about 2mg of vitamin C, and it takes 10mg to prevent scurvy. So, they would have been comparing 2mg a day to like three times that 7mg a day—one vitamin C deficient dose to another vitamin C deficient dose. No wonder there would be no difference in scurvy rates. We evolved eating so many plants that we likely averaged around 600mg of vitamin C a day. That’s what our bodies are biologically used to getting. What about fiber? How much fiber are we used to getting? Over 100 grams a day. The highest fiber intake group in the North Carolina study was eating only 25 grams, which is less than the minimum recommended daily allowance, which is about 32 grams. They didn’t even make the minimum. So they compared one fiber-deficient diet to another fiber-deficient diet—no wonder there was no difference in diverticulosis rates.

The African populations, where they had essentially no diverticulosis, ate diets consisting in part of very large platefuls of leafy vegetables—similar, perhaps, to what we were eating a few million years ago. They were eating plant-based diets containing 70 to 90 grams of fiber a day.

Most vegetarians don’t even eat that many whole plant foods, though some do. At least they hit the minimum mark, and have less diverticulosis to show for it. This was a relatively small study, though. 35 years later, 47,000 people were studied, confirming that consuming a vegetarian diet and a high intake of dietary fiber were both associated with a lower risk of both hospitalization and death from diverticular disease. And they had enough people to tease it out. Compared to those eating a single serving of meat a day or more, those who ate less than half a serving appeared to have a 16% lower risk; pescetarians—no meat except fish—down 23%, though nether statistically significant, but eating vegetarian was 35% lower risk, and those eating strictly plant-based appeared to be at 78% lower risk.

As with all lifestyle interventions, it only works if you do it. High-fiber diets only work if they’re actually high in fiber.

We would love it if you could share with us your stories about reinventing your health through evidence-based nutrition.  Go to nutrition facts.org forward slash testimonials. We may share it on our social media to help inspire others.

To see any graphs charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There you’ll find all the detailed information you need – plus links to all of the sources we cite for each of these topics.

Be sure to check out my new “How Not to Die Cookbook.”  It’s beautifully designed, with more than 100 recipes for delicious and nutritious, life-saving, plant-based meals, snacks, and beverages.  All proceeds I receive from the sales of all my books goes to charity.

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free. There’s no ads, no corporate sponsorship.  It’s strictly non-commercial.  I’m not selling anything. I just put it up as a public service, as a labor of love – as a tribute to my grandmother – whose own life was saved with evidence based nutrition.

Thanks for listening to Nutrition Facts.  I’m your host, Dr. Michael Greger.

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