The wellness industry loves a hero ingredient. The year 2025 was when protein dominated grocery aisles, appearing in everything from popcorn to soda and even water. Now, fibermaxxing is coming for its glory, with the humble nutrient promising not only smoother, more satisfying poops but also benefits for metabolic health, heart health, and then some. But where do probiotics—another gut-health darling that had its own heyday as the supplement du jour a few years back—come into play?
If you’re trying to optimize your gut health and digestion, is it fiber or probiotics that’ll do most of the heavy lifting? Below, experts help us unpack these two gut health all-stars and share which one reigns supreme. But first, a quick refresher on both.
The benefits of fiber
Found in plant foods, fiber is a type of carbohydrate that your body can’t digest—but your gut bacteria can. “When diverse dietary fibers reach your colon, your bacteria ferment them and produce short-chain fatty acids (SCFAs),” says Will Bulsiewicz, MD, a board-certified gastroenterologist and the author of Plant Powered Plus. Butyrate is one important SCFA that helps to not only strengthen your gut barrier and protect your body against pathogens. Beyond the colon, SFCAs also “regulate blood sugar, help manage cholesterol, and trigger the release of appetite-suppressing hormones like GLP-1 and PYY,” says Dr. Bulsiewicz. “They even optimize your immune system and reduce inflammation.” Beyond SCFA production, fiber helps beneficial bacteria thrive and supports the transit and absorption of nutrients in the gut, says Federica Amati, PhD, MPH, RNutr, head nutritionist at ZOE.
And of course, most of fiber’s fame derives from its benefits for digestion, no matter if your issue is too many or too few trips to the toilet…or just a generally uncomfortable experience once you’re there. “Fiber improves bowel irregularity and makes stools bulkier and softer, helping things move through the digestive tract more smoothly,” Felice Schnoll-Sussman, MD, MSc, a board-certified gastroenterologist at Weill Cornell Medicine and New York-Presbyterian, tells SELF.
Depending on your digestive woes, it can also help to get specific about the type of fiber you’re getting. That’s right: There are two kinds—soluble and insoluble fiber—and each serves a different purpose. The former dissolves in water and can help slow digestion, which Dr. Schnoll-Sussman says is helpful for diarrhea and managing blood sugar. (“It can also lower cholesterol by binding to bile acids, which can be associated with a reduced risk of cardiovascular disease and obesity,” she adds.) Insoluble fiber, meanwhile, doesn’t dissolve in water and can help boost transit in the bowel, thus addressing constipation.
The benefits of probiotics
A healthy gut is a diverse one—the more friendly microbes, the better. That’s one of the reasons why probiotic supplements have been gaining momentum in recent years. “Probiotics are live microorganisms you consume with the goal of conferring a health benefit,” says Dr. Bulsiewicz. These friendly bacteria compete with and ultimately crowd out pathogenic bacteria, adds Dr. Schnoll-Sussman.
Many people take (and eat) probiotics for the sake of improving their gut health in general. However, they truly shine in a handful of specific instances. Per Dr. Schnoll-Sussman, targeted strains show the most promise to help those with diarrhea, ulcerative colitis, and irritable bowel syndrome (IBS). “They often make sense to take during or after taking antibiotics,” she adds. That’s because antibiotics wipe out both good and bad bacteria, thus reducing the microbial diversity crucial for your gut and overall well-being.
While probiotics can help recolonize your gut, you have to keep consuming them if you want their benefits to last. “Unlike fiber, a prebiotic which feeds your existing bacteria, probiotics are like calling in reinforcements: temporary backup troops that can help but typically don’t stick around for the long term,” says Dr. Bulsiewicz. Also worth noting: Probiotics aren’t a cure-all for your microbiome, and they work best in an environment that’s being nourished in other ways. “They’re most effective in a gut that’s already been prepared—one with adequate dietary fiber, diversity, and a functioning barrier,” he adds. “A probiotic entering a fiber-rich, metabolically active gut performs far better than one entering an impoverished, starving ecosystem.”
So what’s better: fiber or probiotics?
Drumroll, please: All the experts we spoke to agree that fiber takes the crown as the foundational player for gut health. “Fiber is consistently linked to better overall health outcomes, and it supports the gut microbiome in a way that tends to be more reliable and more scalable than taking a probiotic,” Dr. Amati shares. “Probiotics can be useful, but they are not universally beneficial, and the effects vary a lot by strain, dose, and the person taking them.”
As beneficial as fiber is, the unfortunate news is that you’re probably not getting enough of it. According to the American Society for Nutrition, a mere 7% of adults in the US meet their fiber needs daily. Generally speaking, women should aim for 25 grams a day whereas men should aim for 38 grams a day. To bump up your intake, aim to incorporate diverse fiber sources—such as fruits, vegetables, legumes, whole grains, nuts, and seeds—into every meal and snack. If you still have trouble reaching your goals, a fiber supplement—such as psyllium husk or a soluble fiber mixed into water—can come in handy.
Instead of going from zero to 60 with your fiber intake, take a slow and steady approach. Dr. Amati suggests increasing your fiber gradually over a week or two. “Your gut microbes need time to adapt, and going from low to high fiber overnight can cause bloating and discomfort,” she says. You’ll also need to stay hydrated to keep things moving along. And in case you’re dealing with IBS or other gut sensitivities, you’ll want to be cautious when increasing your intake to avoid exacerbating those symptoms.
The bottom line
All said, fibermaxxing is putting the gut-boosting nutrient in the spotlight at long last, and for good reason. The majority of us would benefit from getting more of it in our daily diets. But that’s not to say that you should totally sleep on probiotics either. (Hot tip: You can always try the 30-30-3 method, which suggests eating 30 grams of fiber daily plus 3 probiotic foods daily to seamlessly get the best of both worlds.)
“The optimal strategy isn’t fiber or probiotics. It’s fiber first, then strategic probiotic support when indicated,” Dr. Bulsiewicz concludes. “If we were building our gut garden, prebiotic fiber is the soil fertilizer and probiotics are the seeds. Start with the foundation by building the garden, then invite the guests who can thrive in it.”
Related:
- 7 Gut Health Myths That Could Be Doing You More Harm Than Good
- The Heart-Healthy Superfood Combo You Should Eat Every Day
- 5 Nutrients Women Need More of After 40
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