Were We Wrong About Fiber?

In my video Is the Fiber Theory Wrong?, I present that fiber-containing foods may not only help prevent heart disease, but also 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 who don’t. But what if we don’t want to have a heart attack in the first place? If 7 grams of fiber gets us a 9 percent reduced risk, would 77 grams a day drop our risk by 99 percent? That’s about how much fiber they used to eat in Uganda, a country in which coronary heart disease, our number-one killer, was almost nonexistent.

Heart disease was so rare among those eating traditional plant-based diets in Uganda that papers were published with such titles as “A Case of Coronary Heart Disease in an African.” After 26 years of medical practice in East Africa, doctors finally recorded their first case of coronary heart disease (in a judge who consumed a “partially Westernized diet,” in which fiber-free foods, such as meat, dairy, and eggs, displaced some of the plant foods in the traditional diet).

Were there so few cases because Africans just didn’t live very long? No, the overall life expectancy was low because of diseases of childhood, such as infections, but, when Africans reached middle age, they had the best survival rates, thanks in part to our number-one killer being virtually absent. Of course, since diets have been Westernized across the continent, coronary heart disease is now their number-one killer as well, going from virtually nonexistent to an epidemic.

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

The “dietary fiber hypothesis,” first proposed in the 1970s, zeroed in on fiber as the dietary component that was so protective against chronic disease. Since then, evidence has certainly accumulated that those who eat lots of fiber appear to be 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. Maybe all these studies showing fiber is good are just showing that eating lots of unrefined plant foods is good. “Fiber is but one component of plant food, and to neglect the other components [such as 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 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 we should go back to eating whole plant foods, he was so convinced fiber was the magic component that his top recommendation was to eat whole grain bread—though they never used to eat any kind of bread in Uganda—and sprinkle some spoonfuls of wheat bran on your food.

However, 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, it might have been 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 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.”

What would have happened if Burkitt and others had emphasized instead the value of plant foods? The value of eating unrefined plant food, which incorporates fiber and phytonutrients, might have been the focus of attention rather than just isolated fiber, which led to people shopping for their fiber in the supplement aisle instead of the produce aisle.


My Solving a Colon Cancer Mystery video is a perfect example of the concept I presented here. If fiber were really the key, then sub-Saharan Africa would be rife with colorectal cancer these days.

For an extreme example, how about disease reversal with a diet centered on white rice? See Kempner Rice Diet: Whipping Us into Shape and Drugs and the Demise of the Rice Diet.

My video The 5-to-1 Fiber Rule discusses a way to identify less processed foods using fiber as a marker of whole foods.

For more intrigue in the world of fiber, check out Does Fiber Really Prevent Diverticulosis?.

And, if you’re thinking, “Dr. Who?,” then, for a historical perspective, see Dr. Burkitt’s F-Word Diet.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Can Oatmeal Reverse Heart Disease?

Fiber continues to be singled out as a nutrient of public health concern. We’re getting only about half the minimum recommended intake on average. There is a fiber gap in America. Less than 3 percent meet the recommended minimum. This means that less than 3 percent of all Americans eat enough whole plant foods, the only place fiber is found in abundance. If even half of the adult population ate 3 more grams a day—a quarter cup of beans or a bowl of oatmeal—we could potentially save billions in medical costs. And that’s just for constipation! The consumption of plant foods, of fiber-containing foods, may reduce the risk for diabetes, heart disease, stroke, cancer, and obesity as well.

The first to make this link between fiber intake and killer disease was probably Dr. Hugh Trowell. He spent 30 years practicing medicine in Africa and suspected it was the Africans high consumption of corn, millet, sweet potatoes, greens, and beans that protected them from chronic disease. This twisted into the so-called “fiber hypothesis,” but Trowell didn’t think it was the fiber itself, but the high-fiber foods themselves that were protective. There are hundreds of different substances in whole plant foods besides fiber that may have beneficial effects. For example, the fiber in oatmeal can lower our blood cholesterol levels so that less gets stuck in our arteries, but there also are anti-inflammatory and antioxidant phytonutrients in oats that can prevent atherosclerotic build-up and then help maintain arterial function (see Can Oatmeal Reverse Heart Disease?).

Visionaries like Trowell were not entrapped by the reductionist “simple-minded” focus on dietary fiber and insisted that the whole plant foods should receive the emphasis. Fiber intake was just a marker for plant food intake. Those with the highest fiber intake and the lowest cholesterol were those whose who ate exclusively plant-based diets.

Risk factors like cholesterol are one thing, but can these individual foods actually affect the progression of heart disease, the #1 killer of Americans? We didn’t know until 2005. Hundreds of older women were subjected to coronary angiograms, where we inject dye into the coronary arteries of the heart to see how wide open they are. Each participant got an angiogram at the beginning of the study and one a few years later, all while researchers analyzed their diets. The arteries of women eating less than a serving of whole grains a day significantly narrowed, whereas the arteries of women who ate just a single serving or more also significantly narrowed, but they narrowed less. These were all women with heart disease eating the standard American diet, so their arteries were progressively clogging shut. But there was significantly less clogging in the women eating more whole grains, significantly less progression of their atherosclerosis. A similar slowing of their disease might be expected from taking cholesterol-lowering statin drugs. But do we want to just slow the rate at which we die from heart disease, or do we want to not die from heart disease at all?

A strictly plant-based diet has been shown to reverse the progression of heart disease, opening up arteries back up. Yes, whole grains, like drugs, can help counter the artery-clogging effects of the rest of the diet. Having oatmeal with bacon and eggs is better than just eating bacon and eggs, but why not stop eating an artery-clogging diet altogether?

Oatmeal offers a lot more than fiber, though. See Oatmeal Lotion for Chemotherapy-Induced Rash and Can Oatmeal Help Fatty Liver Disease?

Trowell’s work had a big influence on Dr. Denis Burkitt. See Dr. Burkitt’s F-Word Diet.

This reminds me of other interventions like hibiscus tea for high blood pressure (Hibiscus Tea vs. Plant-Based Diets for Hypertension) or amla for diabetes (Amla Versus Diabetes). Better to reverse the disease completely.

And for an overview of how whole plant foods affect disease risks, be sure to check out the videos on our new Introduction page!

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Image Credit: Rachel Hathaway / Flickr. This image has been modified.