The Fiber Question Nobody Wants to Answer

Eat more fiber for gut health. You've heard it a thousand times from doctors, dietitians, and cereal boxes. fiber" class="wiki-link" data-wiki-page="/wiki/#fiber">Fiber feeds good bacteria. Fiber keeps you regular. Fiber prevents colon cancer.

Then someone goes carnivore, drops fiber to zero, and their IBS disappears in two weeks. Their bloating stops. Their bowel movements normalize for the first time in years.

How does that work? The answer is more interesting than most gastroenterologists want to admit.

What Fiber Actually Does (And Doesn't Do)

Fiber adds bulk to stool. Insoluble fiber speeds transit time. Soluble fiber feeds gut bacteria through fermentation, producing short-chain fatty acids like butyrate. That's the textbook version. Here's what the textbook skips.

A 2012 study in the World Journal of Gastroenterology put 63 patients with chronic constipation and bloating on a zero-fiber diet. After six months, every single patient on the no-fiber diet reported improvement in symptoms, bloating, and abdominal pain. The high-fiber group? No change. The researchers concluded that reducing fiber intake actually resolved constipation symptoms in this population.

A separate 2019 review in Gastroenterology & Hepatology found that only about 50% of constipation patients respond to fiber supplementation at all. The other half either see no change or get worse. The assumption that fiber universally helps digestion doesn't hold up under clinical scrutiny.

This doesn't mean fiber is bad for everyone. It means the "more fiber fixes everything" advice is too simple, and for a meaningful percentage of people, it's actively wrong.

The Microbiome Adapts Faster Than You Think

Your gut bacteria aren't fixed. They shift based on what you eat. Within 24-48 hours of changing your diet, bacterial populations start reshuffling. Within a week, the dominant species in your gut can look completely different.

A 2014 study published in Nature tracked microbiome changes in people switching between plant-based and animal-based diets. The animal-based diet group saw rapid shifts toward bacteria that specialize in breaking down protein and fat. Bile-tolerant species like Bilophila and Bacteroides increased significantly. These bacteria produce butyrate through different pathways than fiber fermentation, specifically through the breakdown of amino acids like glutamine and lysine.

This is the piece most fiber advocates miss. Your gut doesn't need fiber to make butyrate. It needs bacteria that match your food source, and those bacteria show up within days. The gut is not a static ecosystem. It's a responsive one.

A 2021 study from Cell Host & Microbe confirmed this adaptive capacity, showing that gut microbial diversity stabilizes on an animal-based diet within 10-14 days. The initial drop in certain bacterial species reverses as protein-fermenting species fill the niche. The total diversity metric ends up comparable to omnivorous diets, just with a different composition.

Why Removing Plants Helps Some People

Plant foods contain defense chemicals. These aren't contaminants or toxins added during processing. They're compounds the plants evolved to deter herbivores. Lectins in beans and grains bind to intestinal cells. Oxalates in spinach and almonds form crystals that irritate tissues. FODMAPs in onions, garlic, and cruciferous vegetables ferment rapidly, producing gas. Salicylates in many fruits trigger inflammation in sensitive individuals.

For people with intact digestion and a robust intestinal barrier, these compounds pass through without significant trouble. The gut lining repairs fast enough to keep up. But for people with compromised gut lining (increased intestinal permeability, sometimes called "leaky gut"), these compounds cross the barrier and trigger immune responses. That shows up as bloating, gas, diarrhea, constipation, skin rashes, joint pain, or a rotating mix of all of them.

Estimates vary, but research from Alessio Fasano's lab at Harvard suggests that increased intestinal permeability affects roughly 25-30% of people with chronic digestive complaints. For those individuals, the standard advice to eat more vegetables and fiber can make symptoms worse, not better.

Carnivore removes every plant-based irritant at once. It's the ultimate elimination diet. There's no guessing about which plant compound is the trigger. If your gut calms down on carnivore, you know plants were part of the problem. Then you can test them back one at a time, keeping a food and symptom journal, to find the specific culprit.

IBS and IBD: What 2,000 People Reported

The Harvard-led carnivore diet survey, published in 2021, collected data from over 2,000 participants who had been eating carnivore for at least six months. The digestive health numbers stood out from everything else in the survey.

Among those with diagnosed IBS, 97% reported improvement in symptoms. For inflammatory bowel disease (Crohn's disease and ulcerative colitis), 78% reported improvement. Among participants with chronic bloating or gas, 93% reported partial or complete resolution.

These are self-reported numbers, not double-blind controlled trials. The survey has limitations: selection bias, no control group, no objective biomarker validation. But 97% symptom improvement in IBS is a remarkable signal, especially for a condition where standard pharmaceutical treatments produce response rates of 30-50% in clinical trials.

Dr. Shawn Baker, who helped organize the survey, noted that digestive improvements were the most commonly reported benefit across all respondents, even more frequent than weight loss or energy improvements. About 80% of all participants reported better digestion as a primary outcome.

The Stomach Acid Connection

There's another mechanism at work that gets less attention. A high-protein, high-fat diet stimulates more consistent stomach acid production. Hydrochloric acid in the stomach serves as the first line of defense against pathogens, and it's essential for proper protein breakdown.

Many people with chronic digestive issues actually have low stomach acid (hypochlorhydria), not high. Low acid means food sits in the stomach longer, ferments, and causes reflux that feels like excess acid. Doctors prescribe proton pump inhibitors, which reduce acid further, creating a cycle that makes the underlying problem worse.

Carnivore eating naturally increases stomach acid production because the stomach needs more acid to break down whole-meat meals. Several practitioners, including Dr. Georgia Ede, have documented patients being able to discontinue PPIs within 4-8 weeks of starting a meat-based diet. This isn't a universal outcome, but it's common enough to be worth monitoring.

The Transition Is Rough (Here's Why)

Going carnivore doesn't fix your gut overnight. The first 1-3 weeks can actually feel worse. Loose stools are common, sometimes occurring 3-5 times per day. Bloating can temporarily increase. Some people report nausea after fatty meals.

This is normal and expected. Your gallbladder needs time to upregulate bile production, a process that takes 2-3 weeks to fully adapt. Your gut bacteria are dying off and being replaced. The die-off of certain bacterial species can release endotoxins that cause temporary malaise, sometimes called the "adaptation flu."

Three things help during this transition period. First, eat leaner cuts for the first week: chicken thighs, 90/10 ground beef, sirloin instead of ribeye. Your bile production isn't ready for 70% fat meals yet. Second, add salt liberally to everything, aiming for 5-7 grams of sodium per day. Electrolyte loss accelerates when you drop carbohydrates. Third, don't panic about loose stools. They typically resolve by week 3-4 as bile production catches up and your microbiome stabilizes.

What This Means for Your Gut

If your gut works fine on a mixed diet with plenty of vegetables and fiber, you probably don't need carnivore for digestion. Keep eating your vegetables. They're clearly working for you.

If you've tried fiber supplements, probiotics, low-FODMAP diets, digestive enzymes, and prescription medications without lasting relief, carnivore is worth a 30-day test. The risk is minimal. The potential upside is significant. There are no essential nutrients in plant foods that you can't get from well-sourced animal products during a 30-day trial.

Your gut bacteria will adapt within two weeks. Your digestion will simplify as you remove hundreds of plant compounds from the equation. And you might discover that the fiber you thought you needed was the thing causing problems all along.

Track your symptoms daily during the trial. Note stool quality, bloating, energy, and any skin changes. The data will tell you more than any theory about whether this approach works for your specific gut.