Fiber feeds your colon cells: butyrate and how to eat for it

Key ideas

• The cells lining your colon take much of their energy straight from the colon, as butyrate that bacteria make by fermenting fiber, not from the blood.
• Burning butyrate uses up oxygen, which keeps the colon surface low in oxygen and friendly to the fiber-fermenting bacteria.
• Without fiber, some gut bacteria switch to eating the mucus layer that protects the colon wall. That was shown in mice.
• Fibers ferment at different speeds. Fast ones like inulin are used up early, and slow ones from beans and lentils last to the far end of the colon, where Hank says colon cancer most often shows up.
• Oat fiber lowers cholesterol by carrying bile out of the body, so the liver pulls cholesterol from the blood to make more.
• Add fiber to food you already like, a few grams a day at a time, rather than cutting foods out.

The cells lining your colon get most of their energy not from your blood but from butyrate, a short fat that gut bacteria make when they ferment fiber, and that changes which fiber is worth eating. These are my notes on Hank Green’s video with Liam Layton of The Plant Slant: why colon cells depend on butyrate, why slow-fermenting fiber from beans and lentils reaches the far end of the colon where trouble tends to start, and the low-effort ways Liam adds fiber to food people already like. I’ve added a few questions of my own at the end: whether inulin and other supplements work, how different beans and potatoes compare, and a simple way to cook dried pinto beans.

Why colon cells run on butyrate

Most cells in your body are fed by the blood. Colon cells are the exception Hank builds the video around: they take much of their fuel from inside the colon, and the fuel they’re built for isn’t in your food. It’s butyrate, made by bacteria that ferment fiber without oxygen, the same kind of metabolism that makes yogurt or beer.

The research behind this is old and solid:

• The original measurement. In colon cells taken from 14 people, butyrate accounted for about three quarters of the cells’ oxygen use when it was their only fuel, and it stayed the main fuel even with glucose present, most of all in the descending colon (Roediger, 1980). Hank puts the share at 60 to 70%.
• What happens without it. Colon cells from germ-free mice, which have no bacteria to make butyrate, were starved of energy and began digesting their own contents. Adding butyrate fixed it, and it worked as fuel rather than as a gene switch (Donohoe et al., 2011).

Butyrate also changes how colon cells behave. Hank’s point that it affects which genes they switch on, and how easily they get inflamed, is well established, and it’s one reason researchers link fiber to lower colon cancer risk.

Low oxygen and the mucus layer

The colon surface needs very little oxygen, under 1% in Hank’s telling, so that the fiber fermenters can thrive there. Colon cells help keep it that way: burning butyrate uses a lot of oxygen, so they soak up what’s around. A 2017 mouse study found the mechanism. Butyrate switches on a sensor in colon cells that keeps them burning fat, which keeps oxygen low and stops oxygen-using bacteria such as E. coli and Salmonella from spreading (Byndloss et al., 2017).

The second half of the story is what the bacteria do when fiber runs out. In mice given a human gut community and a fiber-free diet, the bacteria turned to the mucus that colon cells make, a layer of sugar-coated proteins, and ate through it. The thinner barrier let a gut pathogen reach the colon wall and cause severe colitis (Desai et al., 2016). This hasn’t been shown the same way in people, but it’s why Hank says a low-fiber gut is a less stable one.

Which fiber reaches the far end

Fibers aren’t interchangeable, because they ferment at different speeds. A fiber that bacteria break down quickly gets used up in the first part of the colon, and by the end there’s little left to ferment. The far end, the distal colon and the rectum, is where Hank says colon cancer and bowel disease show up most often, and it’s the stretch slow fibers can still feed.

Psyllium still earns its place. It’s a soluble fiber, it firms or loosens stool as needed, and soluble fiber is where most of the cholesterol and blood sugar benefits people associate with fiber come from. It just doesn’t do much for the butyrate story, which is why Hank came away wanting a mix of fibers from whole foods: beans, lentils, leaves, carrots and oats.

How oats lower cholesterol

Liam’s favorite fiber fact is the one about oats. Oats carry beta-glucan, a soluble fiber that thickens what’s in your gut and holds on to bile. Bile is made in the liver from cholesterol, released when you eat, and normally reabsorbed. When beta-glucan carries it out instead, the liver makes more, and the cholesterol for it comes from your blood.

The numbers on this are firm. A meta-analysis of 28 trials found that 3 g of oat beta-glucan a day lowered LDL cholesterol by about 0.25 mmol/L, roughly 10 mg/dL, against controls (Whitehead et al., 2014). That 3 g mark is also the threshold the US and EU use for an oat cholesterol health claim, and a typical bowl of oatmeal carries less than that, so it takes more than one serving a day.

Easy ways to add fiber

Liam’s approach is to add fiber to meals people already eat, not to replace them. Most Americans eat about 16 g of fiber a day (NHANES 2009 to 2010), against recommended amounts of 25 to 38 g, depending on age and sex. He suggests going up by 3 to 5 g a day at a time, since a jump from 10 g to 25 g overnight is what makes people decide fiber doesn’t agree with them.

His low-effort additions, as he describes them:

• Red lentils in sauce. Rinse them, cook them in the microwave with water and blend them into marinara. A quarter cup of cooked lentils adds a few grams.
• White beans in soups and sauces. Blended, they disappear into soups or an Alfredo, which also gets around the texture complaint.
• Baked oats. Mash bananas (or applesauce or canned pumpkin) with oat flour, bake a pan on Sunday, and top a slice differently each morning. Oat flour can be bought gluten-free.
• Farro for rice. It has far more fiber than brown rice, which only beats white rice by about a gram a serving.
• Edamame with avocado. Mash shelled edamame into avocado for toast, which adds fiber and protein and stretches the avocado.
• Dried beans, batch cooked. Cook them in a pressure cooker with onions, peppers and spices, then freeze portions in silicone trays.
• A piece of fruit. A banana has about 3 g and an apple about 4.5 to 5 g. Peanut butter keeps its fiber, and blending fruit into a smoothie doesn’t remove any.

Two of the facts he cites hold up as he states them. In three Harvard cohorts of over 210,000 people, eating peanuts twice a week or more went with 13% lower cardiovascular disease risk than rarely eating nuts (Guasch-Ferré et al., 2017), an association, not proof. And the University of Michigan study he mentions scored about 5,800 foods in minutes of healthy life per serving: a beef hot dog on a bun lost 36 minutes and a peanut butter and jelly sandwich gained 33, the top score (Stylianou et al., 2021). Those minutes come from a model of disease risk, not a measured change in anyone’s lifespan.

Does inulin work well?

This was my own question after the video, since inulin is the fiber in most prebiotic sodas and many “added fiber” products. The short answer: it reliably does a couple of useful things, but it isn’t a substitute for the slow fibers in beans and lentils, and it’s the fiber most likely to cause gas.

The catch is the one Hank names: inulin ferments fast. Most of it is used up early in the colon, so it does little for the distal colon where slow fibers matter most. So inulin works for what it does, feeding bifidobacteria and nudging regularity, and the honest use is as one fiber in the mix. The cheapest way to get it is the food it comes from: onions, garlic, leeks, asparagus and Jerusalem artichokes.

Do supplements help?

My next question was whether any supplement does the butyrate job for you. One has decent evidence, the common ones help in other ways, and butyrate pills have almost none.

Resistant potato starch is plain, unmodified raw potato starch. It only works raw, stirred into something cool such as yogurt or a smoothie, since cooking turns it into ordinary starch. The trial was short and measured butyrate in stool, so it’s a promising result rather than a settled one. A supplement covers the days you don’t eat beans; it doesn’t replace them.

Beans and potatoes compared

All dried beans and lentils carry both fiber and resistant starch, the starch your own gut can’t digest, so all of them feed the slow fermenters. They aren’t equal, but the gap is small enough that the bean you’ll actually eat is the right one. These are fiber figures per cooked cup as nutrition sites report them from USDA data; sources vary a little with cup weight.

Even the lowest gives half a day’s target in a cup, and mixing kinds is better than chasing the top one, since different fibers feed different bacteria. Canned beans count, and rinsing them cuts the salt without losing the fiber. Green beans are a pod vegetable with much less fiber, so they don’t belong on this list.

Potatoes help too, mainly when they’re cooked and then cooled. Cooling turns some of the cooked starch back into resistant starch. One study, as reported by the potato industry, measured about 3.1 g of resistant starch per 100 g in hot potatoes, 4.3 g in chilled ones and 3.5 g in chilled potatoes reheated, so reheating keeps most of the gain. Potato salad and leftover roast potatoes count. Still, a medium potato has about 3 g of fiber, so a cup of beans does several times as much.

A simple pot of pinto beans

Liam’s advice for dried beans is a pressure cooker, plenty of aromatics, and freezing them in portions. Here’s that as one simple pot. A pound of dried pinto beans makes about 6 cups cooked, at roughly 15 g of fiber a cup.

Ingredients: 1 pound dried pinto beans, 1 onion cut in half, 4 garlic cloves, 1 jalapeño cut in half (optional), 1 teaspoon cumin, 1 bay leaf, 2 teaspoons salt.

1. Sort and rinse. Spread the beans out, pick out any small stones or shriveled beans, and rinse them.
2. Soak, if you can. Cover with a few inches of water overnight, then drain and rinse. Soaking cuts the cooking time and, with the water poured off, removes some of the sugars that cause gas. You can skip it in a pressure cooker.
3. Cook. Put everything in the pot with water to cover by about two inches.
   • Pressure cooker: 15 minutes at high pressure if soaked, or 30 minutes if not, then let the pressure come down on its own for 15 minutes.
   • Stovetop: bring to a boil, then keep at a gentle simmer, partly covered, for about 1.5 to 2 hours if soaked, longer if not. Stir now and then and add water if they poke above the liquid.
4. Check. They’re done when several beans are creamy all the way through. Undercooked beans are hard on the stomach, so cook until soft, not just tender outside. Fish out the onion, jalapeño and bay leaf, and taste for salt.
5. Store. Keep a few days’ worth in the fridge in their liquid, and freeze the rest in 1-cup portions.

To eat them, do what Liam does: rice and beans topped with salsa and avocado. Mashed with a little of their liquid in a hot pan, they’re refried beans for tacos or toast. Spooned over a baked potato that’s had a night in the fridge, you get beans and cooled potato in one bowl.

How I’d use this

The practical version is short. Eat a mix of fibers rather than one, and lean on beans and lentils, because they’re the ones that last to the end of the colon. Add them to food you already like, a few grams a day at a time. A pot of dried pinto beans on the weekend, frozen in portions, covers most of a week. Oats are worth a regular slot for cholesterol, a fiber supplement is still worth keeping for what it does, and resistant potato starch is the supplement worth trying for butyrate. A prebiotic soda is a small extra, not the main event. None of this replaces medical advice for a bowel condition, where inulin in particular can make things worse.

Key terms

Colonocytes

The cells that line the colon. They keep microbes out, keep the mucus layer up and replace themselves every few days.

Short-chain fatty acids

Small fats that gut bacteria make when they ferment fiber without oxygen. Butyrate, acetate and propionate are the main three.

Butyrate

The short-chain fatty acid that colon cells burn for fuel. It also changes which genes those cells switch on.

Fermentable fiber

Fiber your own enzymes can't digest but gut bacteria can. How fast they ferment it decides how far along the colon it lasts.

Distal colon

The last stretch of the colon, the descending and sigmoid colon, before the rectum.

Resistant starch

Starch your own gut can't digest, so it reaches the colon and gets fermented. Beans, cooled potatoes and raw potato starch carry it.

Inulin

A fermentable fiber found in chicory root, onions, garlic and leeks, and added to many prebiotic sodas and fiber products.

Beta-glucan

The soluble fiber in oats and barley. It thickens gut contents and binds bile.

Psyllium

A soluble fiber from plantago seed husks, sold as Metamucil. It forms a gel and is only partly fermented.

Quotes from the talk