Thank you Camilla, Marg KJ, Suzette Jensen, Roxy Fort, and many others for tuning into my live video with Chris Miller MD!
We went live today with a question that comes up all the time and can make people feel genuinely confused.
If fiber is so good for us, why do some people feel amazing when they increase it… and others feel bloated, gassy, inflamed, or just plain worse?
Dr. Chris Miller and I unpacked what’s going on, why it’s not “in your head,” and what a smarter stepwise approach can look like.
This live was based on Dr. Miller’s most recent article, which I’ll link below along with her Substack and her practice website.
The premise: Fiber is still the goal, but the path matters
Both of us teach fiber. The long-term data is compelling, and in most people a higher-fiber, more plant-forward pattern is associated with better health outcomes.
But in real life, we see two very different experiences:
Some people increase fiber and get all the “expected” benefits, better digestion, lower inflammation, clearer skin, improved cholesterol, improved blood pressure.
Other people increase fiber and get gas, bloating, discomfort, and sometimes signs that inflammation is actually going up.
So we asked: what’s different about the second group?
The Stanford study that changed how Dr. Miller practices
Dr. Miller described a Stanford study published in 2021 that helped explain this divide.
Participants were assigned to one of two approaches for about 10 weeks:
* High-fiber group: worked up to at least 45 grams of fiber per day from plant foods (vegetables, fruit, legumes, whole grains, nuts, seeds).
* Fermented foods group: worked up to about six servings per day of fermented foods.
The researchers expected the high-fiber group to have the best microbiome and immune improvements. That is not what happened.
What stood out:
* The fermented foods group showed a consistent increase in microbiome diversity and a drop in inflammatory markers.
* The high-fiber group had mixed results: some improved, some barely changed, and some had increased inflammation and no meaningful rise in microbiome diversity.
Even when the groups crossed over, the fermented foods pattern continued to show a strong signal toward lower inflammation.
The “why”: You can’t benefit from fiber if you don’t have the gut bugs to use it
Here’s the key idea Dr. Miller emphasized.
Fiber is not digested by us. It’s digested by our gut microbes.
When your gut ecosystem is diverse and functional, fiber gets fermented into helpful compounds (including short-chain fatty acids) that support the gut lining and calm inflammation.
But if your microbiome is narrow, damaged, or out of balance, and you suddenly “flood the system” with fiber, you may not have the microbial machinery to process it. The result can be gas, bloating, discomfort, and sometimes more inflammation.
So in those people, the smarter move may be:
Build tolerance and microbial diversity first, then gradually increase fiber.
What narrows the microbiome in the first place?
We talked through common reasons gut diversity can shrink over time, including:
* Years of low-fiber eating (little to no food reaching the colon for microbes)
* Antibiotic exposure
* Chronic stress and poor sleep
* Environmental exposures and pollutants
* Ultra-processed foods and additives that disrupt gut balance
* Early-life factors such as C-section delivery and limited microbial exposure
Then we widened the lens to practical ways people can support diversity outside of food:
Time outdoors, exposure to nature, gardening, travel, interacting with other people, and yes, even pets.
Fermented foods help, but not always and not for everyone
The headline from the study makes it tempting to say, “Everyone should eat a ton of fermented foods.”
But Dr. Miller made an important clinical point: some people do not tolerate fermented foods well, especially:
* People with autoimmune disease during an active flare
* People with histamine intolerance or mast cell activation issues
* People with significant dysbiosis who are not ready for that “bioactive load” yet
For those people, the priority is calming the gut and immune response first, then building back up gradually.
“Put out the fire before you start planting”
This ended up being a central metaphor in our live.
If the gut and immune system are inflamed and reactive, the immediate goal is not to force more fiber or fermented foods. The goal is to reduce the reactivity.
Dr. Miller talked about strategies that can help people ease in:
* Starting with gentler forms of fiber (often cooked, blended, or softened foods before big jumps in raw/high-fiber legumes)
* Using anti-inflammatory foods and spices (she mentioned options like ginger, turmeric, and berries)
* For histamine issues, using a stepwise plan that may include lower-histamine choices and targeted support, sometimes with medication under physician supervision depending on the case
The goal is always temporary support to calm things down so you can eventually return to a more robust, fiber-rich, diverse plant pattern.
Dr. Miller’s personal story: “I thought it was my fault”
Dr. Miller also shared that she has lived this from the inside.
When she first tried increasing fiber during a period of active illness, she felt worse. She had major food sensitivities and histamine reactions, including rapid joint pain after foods many people consider “healthy.” Beans were not possible for her at that time.
She kept thinking she must be doing something wrong.
But what she learned (and what this study helped validate) is that sometimes the body isn’t ready yet. With a stepwise approach and calming inflammation first, she was able to rebuild tolerance over time.
That’s the message I wanted everyone to hear.
If you struggle with fiber, it’s not a moral failing. It’s a physiology problem with a physiology solution.
Practical benchmark to aim for once you’re tolerating fiber
When things are stable, the focus becomes:
Diversity.
Not eating the same “healthy” foods on repeat, but rotating fruits, vegetables, legumes, whole grains, nuts, seeds, herbs, and spices so your microbes have a wider menu.
During the Q&A, someone asked about what I’ve been adding to oatmeal. I shared a simple hack:
Lupini bean flakes (L-U-P-I-N-I).
I mix them into oatmeal, add them to stews, blend them into smoothies, and even stir them into chili. They’re mild tasting and can be an easy way to increase fiber and protein for many people. If you try them, check that the ingredient list is just “lupini bean flakes.”
A quick note on what’s coming next
I also shared that I’m building a new series next year called Mini Medical School, monthly series with mini courses, plus more live interviews and mini Substack summits with collaborators (including Dr. Miller), along with Culinary Healing content with Chef Martin Oswald.
Link to the One Tiny Healing Habit store where you can check how to wear your Healing Habit and share it with others!
More soon on all of that.
Links to Dr. Chris Miller
Here are the links mentioned in the live:
* Dr. Chris Miller’s article: Not Everyone Thrives on High-Fiber Diets. This Study Explains Why
* Dr. Chris Miller’s Substack
* Dr. Chris Miller’s website: ChrisMillerMD.com
