The Fiber Man Was Right About Your Gut, Mostly

If you're past 50, your gut may have started to talk back. Bloating shows up more often. Trips to the bathroom get less regular. And the drugstore now has a whole aisle of pills that claim to fix it.

But your gut doesn't run on pills. It runs on what you feed the trillions of germs that live in it. Feed them well, and they make a fat called butyrate that helps keep your gut wall sound.

So what do those germs need? Four things, and each one has a test behind it. The story starts with a surgeon who asked people for their stools…

On February 14, 1966, Denis Burkitt came back to England from Uganda. He had worked at Mulago Hospital in Kampala since 1948.

In England, he noticed a pattern. Bowel cancer was rare in rural Africa and common in Britain. Why?

To find out, he got reports each month from over 140 rural hospitals in Africa and India. Then he did a thing few doctors would do. He asked people for their stools.

In 1970, on a trip to Uganda, he collected three stools from each Pokot villager he tested. He timed how long food took to pass through them.

In South Africa, a scientist named Alec Walker had already timed it. Food often moved through rural Africans in about half the time it took in white subjects.

In December 1972, Burkitt, Walker and a London surgeon, Neil Painter, laid it out in The Lancet. People on rural, high-fiber diets passed bigger stools, and food moved through them faster. Burkitt blamed low-fiber Western diets for many of Britain's bowel diseases. He soon became known as the Fiber Man.

Was he right? Partly. And the part he missed is the part that matters most for your gut today…

Fiber Does Two Jobs

Burkitt saw fiber as a broom. It adds bulk to your stool and moves it along. That part holds up.

But fiber has a second job he couldn't see in 1972. It feeds your gut germs.

Your body can't digest most fiber, so it reaches your colon whole. There, germs eat it. As they eat, they make several kinds of fatty acid, and butyrate is one of them.

In 2019, Andrew Reynolds at the University of Otago in New Zealand led a review for the World Health Organization. His team pooled 185 long-term studies and 58 trials.

People who ate the most fiber had 15 to 30 percent fewer deaths, from all causes and from heart disease, than those who ate the least. Most of that came from studies that watched people, so it shows a link, not proof. The best results came at 25 to 29 grams of fiber a day.

The 2020 to 2025 Dietary Guidelines for Americans say over 90 percent of women and 97 percent of men fall short.

Range Counts, Not Just Grams

In 2018, Daniel McDonald and Rob Knight at the University of California San Diego reported on 11,336 people. Each one mailed in a stool sample for the American Gut Project.

People who ate more than 30 kinds of plants a week had a wider mix of gut germs than those who ate 10 or fewer.

Here's the thing. That match-up was just 41 people against 44, and they filled in their own food forms. It's a clue, not a rule. Still, it costs you nothing to try…

The Fermented Twist

In 2021, a Stanford team led by Justin Sonnenburg and Christopher Gardner split 36 healthy adults into two groups for 10 weeks. One group ate more fiber. The other ate more fermented foods, like yogurt, kefir, kimchi and kombucha.

Now the surprise. More fiber did not widen the germ mix in 10 weeks. Their germs did gain more tools to break fiber down.

That doesn't make fiber useless. It means a test with 18 people per group, run for 10 weeks, is small and short.

Slow Starch From Cold Rice

Some starch dodges your digestion and reaches your colon like fiber. Scientists call it resistant starch. Call it slow starch from here on.

Cooking a starchy food and then chilling it makes more slow starch.

In 2015, Steffi Sonia's team at Universitas Indonesia in Jakarta tested white rice. Fresh rice had 0.64 grams of slow starch in each 100 grams. Rice kept in the fridge for 24 hours, then warmed up, had 1.65 grams. That's about two and a half times as much.

In 15 healthy adults, the chilled rice also raised blood sugar less than fresh rice did.

Do your germs use it? In 2019, Thomas Schmidt's team at the University of Michigan gave 174 young adults a fiber powder each day for two weeks. Raw potato starch, a slow starch, raised butyrate the most.

But not in everyone. How much butyrate a person made hung on the germs they had at the start. So the same food can do more for one gut than for another.

Plant Compounds And The Cocoa Test

Plants also carry polyphenols, the compounds behind the color and bite of berries, tea and cocoa. Call them plant compounds from here on.

In 2011, Xenofon Tzounis and Jeremy Spencer at the University of Reading in England tested them on gut germs. For four weeks, 22 healthy people drank a cocoa drink each day, either high or low in plant compounds. Then they swapped.

On the strong drink, two germ groups often called friendly, bifidobacteria and lactobacilli, went up. A third group, clostridia, went down. C-reactive protein, a blood marker of swelling, fell too.

Two catches. The drink was a special one with 494 mg of plant compounds a day, not a candy bar. And the work had support from Mars, the candy company, with a Mars scientist among the authors.

Where The Pills Fall Short

In 2018, Eran Elinav's team at the Weizmann Institute in Israel gave 21 people a course of antibiotics. After that, some took a common probiotic pill. Others got back their own gut germs, taken from their stool before the antibiotics. A third group did nothing.

The probiotic kept people's guts from getting back to normal for months. The people who did nothing recovered faster.

That's one small study. It doesn't prove every probiotic fails. But it's a good reason to ask your doctor before you buy one…

Three Things Worth Knowing

Burkitt asked people for their stools because he wanted the plain truth about the gut. He got the broom part right. The germs he couldn't see turned out to be the other half of the story.

So feed them. Give them enough fiber, many kinds of plants, a fermented food each day, and some chilled rice for slow starch.

Start tonight. Put one plant on your plate that you haven't eaten this week, and write it on the list.

Stay well,
The Healing Plate