Carnivore diet constipation is a real question people ask before they try an all-meat approach, and the honest answer is: it depends on the person, the water intake, and how the gut adapts. In the film, Dr. Mike raises the question himself on day 3, worried the burgers could block him up. The evidence on fiber and stool frequency is mixed, not a simple case of no fiber, no bowel movements.
Does a carnivore diet cause constipation?
Carnivore diet constipation is the fear behind a lot of the questions I get about this project. On day 3 of the burger phase, the film shows Dr. Mike asking out loud whether the burgers could block his gut — he was 60 patties in at that point (the film shows, F12). It wasn’t a throwaway line. He’d already noticed something was off with digestion, and he said so on camera before he had any way of knowing how the rest of the month would go.
I’m not a physician and I’m not diagnosing anything here. What I can tell you is what the camera caught, what he wrote down, and what the published research says about fiber and meat-only eating. Those are three different kinds of information and I’m going to keep them separate.
What did the film actually show about his gut?
The film shows Dr. Mike describing 10 minutes to 3 hours of discomfort after every single meal, and he said it was mildly increasing day by day (the film shows, F26). That’s not the same thing as constipation specifically — it could be bloating, cramping, or something else entirely — but it’s the on-camera evidence of a gut that wasn’t happy with the volume or the composition of what was going in.
The book adds detail the final cut doesn’t have room for. By day 9 he described roughly round-the-clock stomach pain alongside poor sleep, in the the book (B17). Read together with the day 3 question, it looks like a gut that was struggling early and didn’t fully settle. I’m not going to tell you what his labs eventually showed — that’s the whole reason to watch the film — but the discomfort itself was on camera well before any test results came back.
If you aren't testing, you're guessing. I wanted to quantify literally everything.
Carnivore diet constipation: what does the evidence say about fiber?
The textbook worry is simple: no plants, no fiber, no bulk, no regularity. The research is less tidy than that. A cross-sectional survey of 2,029 self-reported carnivore dieters found high satisfaction and few reported adverse effects overall, though it’s self-reported with no controls and can’t show cause and effect (the evidence says). That doesn’t mean nobody gets constipated on carnivore — it means a survey of people who stuck with it long enough to answer a survey mostly didn’t report it as their top complaint.
A separate narrative review looked at whether an all-animal-food diet can meet essential nutrient needs at all, and concluded the question is still open, in part because ketosis itself changes what the body requires (the evidence says). Fiber and micronutrient adequacy are tangled together on a diet with zero plant matter, and this review doesn’t settle it either way — it’s a review, not new data.
Do you need fiber to have a bowel movement?
The film suggests, through Dr. Mike’s own on-camera nutrition count, that even 20 burger patties a day still left him tracking a fiber number — he read it out as part of his daily macros (the film suggests, F11). I want to flag that clearly: that 20 gram fiber figure is his own estimate from label data, not a lab assay, and it looks high for plain beef patties. Quote it as his count, not as a settled fact about how much fiber is actually in a burger.
What that tells you practically: people on very low-fiber diets don’t uniformly stop having bowel movements. Stool bulk changes, frequency can change, and some people adapt within weeks while others don’t. None of the studies in front of me directly measured stool frequency on carnivore versus a fiber-containing diet over 30 days, so I’m not going to invent a number that isn’t there.
Is there such a thing as low-residue eating, and does it slow digestion?
Low-residue is the clinical term for diets that leave little undigested material behind — mostly animal protein and fat, no fibrous plant matter. The idea that this could slow transit time is plausible on paper, but I don’t have a linked figure in front of me that measures transit time specifically on a burger-only protocol, so I’m leaving that number out rather than guessing at one.
What I can point you to is a related question — how meat itself is processed. One review found diet-induced thermogenesis, the energy cost of digesting food, is highest after protein and lowest after fat, which tells you protein-heavy eating asks more of the digestive system in a different way (the evidence says). That’s about calorie burn, not stool frequency, but it’s a reminder that an all-meat, high-protein plate is metabolically different from a mixed plate, not just lower in fiber.
Dr. Mike’s own on-camera note about “meat sweats” is worth mentioning here too — he said some people react to as little as 8 ounces of meat, though he was clear there’s very little research on it (the film shows, F40). Different symptom, same theme: individual reactions to large amounts of meat vary a lot.
What's Jim's take on meat and gut regularity?
In my experience, the gut adapts to almost anything you throw at it consistently, but the adaptation period is real and it isn’t always comfortable. I watched Dr. Mike go from fine to uncomfortable within days, and I’ve talked to enough people trying carnivore or strict keto to know that early gut symptoms are common and usually not permanent — but individual results vary, and I’m not qualified to tell you what your gut will do.
I already wrote up the broader digestion picture — fiber, probiotics, and what changes when you cut carbs — in a separate post on gut health, and that’s where I’d send you for the fuller mechanism. This one is specifically about what the burger month showed and what the published research does and doesn’t confirm.
Should you worry about constipation before trying carnivore or keto?
If you’re considering cutting fiber hard, pay attention early — the film shows Dr. Mike noticing discomfort by day 3, not day 20 (the film shows, F12). Watching for how your own body responds in the first week or two seems more useful than assuming either outcome ahead of time.
This isn’t medical advice, and I’m not a doctor. If you want to see exactly how his digestion, and everything else, played out over the full 30 days, that’s what the film and the book cover in detail.
Frequently asked questions
Does carnivore diet constipation happen to everyone?
No. A survey of over 2,000 self-reported carnivore dieters found high satisfaction and few reported adverse effects, though that's self-reported data without controls, so it can't prove what happens to any one person.
Did Dr. Mike get constipated during the 600-burger month?
The film shows him asking on day 3 whether the burgers could block his gut, and describing 10 minutes to 3 hours of discomfort after meals; I'm not going to state the specific outcome here — watch the film for that.
Do you need fiber to digest meat properly?
The research is unsettled; one review found the question of whether an all-animal diet meets nutrient needs is still open, and I don't have a sourced figure on fiber's specific role in stool frequency on carnivore.
Can eating too much meat at once cause gut discomfort?
Dr. Mike noted on camera that some people react to as little as 8 ounces of meat with what's called meat sweats, though he said there's little research on the phenomenon.
Is low-residue eating the same as constipation risk?
Low-residue describes diets that leave little undigested material behind, which is plausible as a mechanism, but I don't have a sourced figure measuring transit time on a burger-only protocol specifically.
The Bottom Line
Carnivore diet constipation isn’t a guaranteed outcome, but early gut discomfort is common enough that it’s worth watching for in the first week or two rather than assuming it either way. In my experience, and based on what the film shows from day 3 onward, the gut reacts fast to a sudden all-meat load, and how it settles after that varies person to person.
If you want to see how it actually played out for Dr. Mike over the full 30 days, along with the bloodwork that went with it, watch The Keto Project on Amazon and read 600 Burgers in 30 Days.
Sources
- Lennerz et al. 2021 — Behavioral Characteristics and Self-Reported Health Status among 2029 Adults Consuming a Carnivore Diet
- O'Hearn 2020 — Can a carnivore diet provide all essential nutrients?
- Westerterp 2004 — Diet induced thermogenesis
The clips
This article is for information only and is not medical advice. Individual results vary. Speak to a qualified clinician before changing how you eat.
The whole experiment is in the film. 600 burgers, 30 days, every blood test — and the ending we never post.
Watch The Keto Project on Amazon