Fiber to Butyrate¶
Run the Fiber to Butyrate MicroSim Fullscreen
About This MicroSim¶
Your own enzymes can't digest dietary fiber, so it travels to the colon, where gut microbes ferment it. Fermentation makes gas and three main short-chain fatty acids (SCFAs): acetate (usually the most abundant), propionate, and butyrate. In people, the colon lining takes up butyrate, the liver takes up much of the propionate, and acetate travels on to the rest of the body.
This MicroSim draws the colon as a tube. Green strands of fiber enter on the left. Colored bacteria ferment them into blue acetate, orange propionate, and red butyrate dots. Butyrate dots move into the row of colonocytes (colon-lining cells), which glow brighter as their fuel rises, while the gaps between cells (the tight junctions) seal more tightly. Three meters track fermentation, colonocyte fuel, and the tight junction seal.
A separate purple panel with a dashed border shows two findings from germ-free mice only: microglia (the brain's immune cells) mature, and the blood-brain barrier tightens, when microbes are present (bars) compared with germ-free mice (black lines). The panel stays fixed when you move the sliders, because those studies compared mice with and without microbes, not different amounts of fiber. These effects have not been shown in people, and the panel can be hidden to make that point.
How to Use¶
- Start at the default (16 grams of fiber a day, about the US average, and medium diversity). Predict which SCFA dots will be most common. Press Start.
- Watch which dots move into the colon wall. Notice that only butyrate does.
- Drag Fiber to 0, then to 30 grams a day. Watch the three meters and the color of the colonocytes.
- Set fiber to 25 grams and drag Diversity from very low to very high. Compare the colonocyte fuel meter.
- Uncheck Show mouse-only panel. Notice that nothing in the human part of the model changes, and read the message that replaces the panel.
- Press Reset to return to the starting settings.
Learning Objective¶
Bloom level: Understand. The learner will trace dietary fiber through bacterial fermentation to acetate, propionate, and butyrate and their effects on colonocytes and tight junctions, and distinguish these from brain effects shown only in germ-free mice.
Iframe Embed Code¶
<iframe src="https://aaryavvatts-lab.github.io/gut-brain-textbook/sims/ch06-fiber-to-butyrate/main.html" height="712px" width="100%" scrolling="no"></iframe>
Lesson Plan¶
Grade level: 9 to 12 (biology, health science, or nutrition science)
Duration: 20 to 25 minutes
Activity:
- Warm-up (3 minutes). Ask: "What happens to the part of a bean that your body can't digest?" Collect a few guesses.
- Explore (8 minutes). In pairs, students run steps 1 to 3 of How to Use and record the three meter levels at 0, 8, 16, 25, and 35 grams of fiber.
- Test a variable (5 minutes). Students hold fiber at 25 grams and record colonocyte fuel at each diversity level, then describe the pattern in one sentence.
- Evidence check (5 minutes). Students explain why the mouse-only panel has a dashed border and write one sentence a news headline could use that stays accurate.
- Limits (3 minutes). Read the "What this model leaves out" box in Chapter 6 and name one thing the sim oversimplifies.
Assessment questions:
- Why does fiber reach the colon when most starch from the same meal doesn't?
- Which SCFA do colonocytes use most, and which SCFA is usually most abundant in the blood?
- In the model, why does the tight junction seal never drop to zero, even with no fiber?
- What kind of animal was used in the studies behind the purple panel, and why does that matter?