Darn it poop, why aren't you blue?, I thought as I stared into the toilet desperately trying to determine why the color of my number two hadn't strayed from the standard. I've done a lot of weird stuff in the name of gut health, but purposely trying to turn my poop blue had to be the most out there. (Even more than the next coolest thing I've tried in the name of digestive wellness, which was testing an at-home microbiome test kit called Viome, $150. What I learned about my overall health from that experience was fascinating.)
Maybe I should back up and explain why the heck I was attempting to turn my poop blue in the first place. As you may or may not know—depending on how much the topic of digestive health excites you—there's a lot your poop can tell you about your health. Frequency, texture, and color are all clues. Recently, gut health company Zoe published a scientific study in the peer-reviewed journal Gut about what gut transit time—a term that refers to how long it takes to poop out what you ate—can specifically tell someone about not only their gut health, but their health in general.
In the study, the researchers tracked the gut transit time of participants by having them eat muffins dyed a vibrant Cookie Monster shade of blue. This way, it would turn their poop blue and the participants would know their excrement was specifically from the muffins and not something else they ate. "We found that by eating a bright blue muffin, developed by our scientists, and seeing when your poop turns blue, we can generate a basic snapshot of your gut health based on your gut transit time," a publicist for the company emailed me. In fact, Zoe was willing to send me blue muffins for the chance to learn about my gut transit time. Would I want to give it a try?
Cut to me looking into the toilet bowl staring at my poop. But in addition to just doing the experiment, I also spoke with gut experts at Zoe and a G.I. doc unaffiliated with the company to learn more about what gut transit time can tell someone about their health—and what an ideal gut transit time looks like.
Why gut transit time matters
The blue muffins were mailed to me ready to eat; no baking required. I usually have oatmeal or a protein bar in the morning, so the opportunity to eat muffins for work was a welcome one. I sliced my muffins open, topped each side with butter, and popped them in the microwave—because blue or not, muffins are meant to be enjoyed.
At 9:15 a.m., I ate my blue muffins with an oat milk latte and got to work. See you on the other side. I forgot about them until 11:45 a.m. when I got the urge to, well, you know. I was disappointed when I saw that my business wasn't blue. Around 1:30 p.m., I opted for a salad for lunch thinking the fiber might help move things along. At 6:30 p.m., alas, a repeat of my 11:45 a.m. performance—no blue. It wasn't until 8:45 a.m. the next morning that I finally saw what I'd been expecting: poop that looked like it came from a Smurf. Okay cool, mission accomplished. Now I wanted to know: Was I normal? How long should it take to poop?
"Gut transit time is very important because it's not just the microbes themselves that are important, but also the ability to move the microbes. If your colon is stagnant, [bad] bacteria will accumulate," says Sabine Hazan, MD, author of Let's Talk Sh!t ($15) and gut health expert unaffiliated with Zoe.
When I spoke with nutritional sciences professor Sarah Berry, PhD, and genetic epidemiology professor Tim Spector, MD—who both worked on the Gut study and work with Zoe—they also explained to me why exactly gut transit time matters and how long it should take. Dr. Spector explained that the importance of gut transit time hasn't really been recognized until recently; the Bristol stool chart—a poster of different types of poo—has long been used to glean information about what poop can tell someone about their digestive health. "We wanted to see if we could get a measure that would give people better information about the microbes and their overall health," Dr. Spector says. And through scientific research, he says that they did, in fact, find that transit time was a more informative measurement.
So, what's the ideal gut transit time?
Of the 863 people who took part in the study, the gut transit time ranged from four hours to several days. "What we saw on average was a correlation between faster transit time and a healthier-looking gut microbiome," Dr. Spector says. "The diversity of [good gut bacteria] was higher in people who had a short transit time and the diversity was lower in people who had a long transit time. The correlations, he says, were more accurate than using the Bristol stool chart to determine how diverse in good bacteria someone's gut was. This is exactly, they say, why knowing your gut transit time is so beneficial. A microbiome swimming with diverse good gut bacteria isn't just indicative of digestive health; it's linked to better overall health, including brain health and lower rates of depression.
Dr. Berry says that previous gut transit studies indicate that the healthiest time fell between 14 and 50 hours, and they found that the majority of people did fall within that range. But Dr. Spector says that based on what they found, a gut transit time of less than 24 hours should be ideal. Dr. Hazan is a bit more liberal with what she feels is optimal. "Just because you're not having a bowel movement every day doesn't mean there's something wrong with you," she says. If you only poop every two days but feel good overall with no bloating or discomfort, she says it's not worth worrying about. "In my opinion, consistency is more important," she says. "If you're used to pooping once a day but then start experiencing diarrhea several times a day or you start only going every few days, that's more something to pay attention to."
Dr. Spector points out that using dye to track gut transit time isn't new; it's done in hospital and clinical settings by gastroenterologists. "Another way doctors also track transit time is with 'smart pills,' which you can actually track on your phone or a monitor, but they're very expensive," Dr. Berry adds. Both agree that eating blue muffins is a more accessible way for people to learn about their gut health.
How to improve gut transit time
But surely it has to be more complicated, I asked, probing the experts. For example, what if in addition to eating the blue muffins, one person ate fiber-rich foods during the day while someone else ate carb- and fat-filled foods. Wouldn't that affect how quickly the muffins were digested?
That's precisely the point, they told me. "As long as you eat the muffins on a day where you're eating what you would normally be, that's going to give you an accurate snapshot of your gut health," Dr. Berry said. "If you eat another blue muffin the next day, the transit time will be the same."
I decided to eat more blue muffins to see if she was right. (Fine, I also wanted muffins for breakfast again.) She was. My gut transit time was roughly the same. Since my gut transit time was also just under 24 hours, it also meant I could work to improve it. Both Dr. Spector and Dr. Berry emphasize that anyone who goes several days without a bowel movement or, on the other end of the spectrum, experience diarrhea several times a day should definitely book some time with a G.I. doc. But they also hope even people falling within the "normal" range of 14 to 50 hours will think about how they can improve their gut transit time through diet. For example, could you be eating a wider range of nutrient-rich foods?
Zoe has a tool to help someone improve on this front, which I tried to see what I could put into practice for myself. Anyone who makes the blue muffins can take a quiz where they input some quick stats about themself and their gut transit time. They're "matched" with a participant from the clinical trial who got similar results. (The participant's name is changed when matched to protect their identity.) Then you can see how many different types of good gut bacteria they have. My match had nine of the 15 types of good gut bacteria strains the study participants were looking for; the logic is that I likely have around nine as well. Along with my results, I was told to try to eat five new types of plants a week to up my gut bacteria diversity. Seems reasonable, I mused.
Watch the video below to learn more about the best foods for gut health:
Stress was something else I asked Dr. Berry and Dr. Specter about. Anyone who has ever had nervous poops before a big event can tell you that stress can have a direct effect on gut transit time. The experts agreed that this is true and it's a gut transit time factor they're hoping to include in their newest research. "The way stress affects transit time is so individual; there's not a simple formula where we can say stress doubles or halves the transit time, it's not that simple to figure out," Dr. Specter says.
But knowing your gut transit time, in general, is a helpful place to start. The blue muffins can help you pinpoint it, but Dr. Spector also says there's another food you can eat and easily see on the other end: corn. Either way, you'll end up, er, flushed with knowledge.
- Asnicar, Francesco et al. “Blue poo: impact of gut transit time on the gut microbiome using a novel marker.” Gut vol. 70,9 (2021): 1665-1674. doi:10.1136/gutjnl-2020-323877
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