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:

9 out of 10 That Die From it Never Knew They Even Had This Preventable Disease

Diverticula are out-pouchings of our intestine. Doctors like using a tire analogy: high pressures within the gut can force the intestines to balloon out through weak spots in the intestinal wall like an inner tube poking out through a worn tire tread. You can see what they actually look like in my video, Diverticulosis: When Our Most Common Gut Disorder Hardly Existed. These pockets can become inflamed and infected, and, to carry the tire analogy further, can blow out and spill fecal matter into the abdomen, and lead to death. Symptoms can range from no symptoms at all, to a little cramping and bloating, to “incapacitating pain that is a medical emergency.” Nine out of ten people who die from the disease never even knew they had it.

The good news is there may be a way to prevent the disease. Diverticular disease is the most common intestinal disorder, affecting up to 70% of people by age 60. If it’s that common, though, is it just an inevitable consequence of aging? No, it’s a new disease. In 1907, 25 cases had been reported in the medical literature. Not cases in 25% of people, but 25 cases period. And diverticular disease is kind of hard to miss on autopsy. A hundred years ago, in 1916, it didn’t even merit mention in medical and surgical textbooks. The mystery wasn’t solved until 1971.

How did a disease that was almost unknown become the most common affliction of the colon in the Western world within one lifespan? Surgeons Painter and Burkitt suggested diverticulosis was a deficiency disease—i.e., a disease caused by a deficiency of fiber. In the late 1800s, roller milling was introduced, further removing fiber from grain, and we started to fill up on other fiber-deficient foods like meat and sugar. A few decades of this and diverticulosis was rampant.

This is what Painter and Burkitt thought was going on: Just as it would be easy to squeeze a lump of butter through a bicycle tube, it’s easy to move large, soft, and moist intestinal contents through the gut. In contrast, try squeezing through a lump of tar. When we eat fiber-deficient diets, our feces can become small and firm, and our intestines have to really squeeze down hard to move them along. This buildup of pressure may force out those bulges. Eventually, a low-fiber diet can sometimes lead to the colon literally rupturing itself.

If this theory is true, then populations eating high­-fiber diets would have low rates of diverticulosis. That’s exactly what’s been found. More than 50% of African Americans in their 50s were found to have diverticulosis, compared to less than 1% in African Africans eating traditional plant-based diets. By less than 1%, we’re talking zero out of a series of 2,000 autopsies in South Africa and two out of 4,000 in Uganda. That’s about one thousand times lower prevalence.

What, then, do we make of a new study concluding that a low-fiber diet was not associated with diverticulosis. I cover that in my video Does Fiber Really Prevent Diverticulosis?

For more on bowel health, see:

What if your doctor says you shouldn’t eat healthy foods like nuts and popcorn because of your diverticulosis? Share with them my Diverticulosis & Nuts video.

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: