Registered dietitian Steph Grasso explains why fiber diversity, prebiotic foods, and lifestyle habits are the real foundations of gut health.
You often talk about fiber as a cornerstone of gut health. What’s the most overlooked benefit of fiber in relation to digestion?
One of the most overlooked benefits of fiber when it comes to digestion is that it’s not just about getting enough fiber, but it’s about getting a variety of fibers. I talk a lot about fiber quantity because most Americans still aren’t meeting the general recommendation of about 25–38 grams per day, but diversity matters just as much, because different fibers do different things in the digestive system.
Some fibers help add bulk to stool and support regular bowel movements, while others absorb water and help soften stool. Certain fibers act as prebiotics, meaning they feed beneficial gut bacteria, which can support everything from digestion to immune and metabolic health. Others help slow digestion, which can support more stable blood sugar and longer-lasting fullness. That’s why I encourage people to think beyond just taking a fiber supplement or eating one “healthy” food every day.
A diverse intake of fruits, vegetables, beans, whole grains, nuts, seeds, and different plant foods throughout the week helps expose the gut microbiome to a wider range of fibers, and that variety is what helps create a more resilient, well-functioning digestive system.
From your perspective, what does it actually mean to have a healthy gut microbiome?
It really means you have a gut environment that is diverse, resilient, and well-nourished. I like to explain the gut microbiome as an ecosystem, almost like a garden. You have trillions of bacteria living in the digestive tract, and the goal isn’t to eliminate bacteria; it’s to support the growth of beneficial microbes that help your body function well. When that ecosystem is supported, it can help with things people actually notice in everyday life: more regular digestion, less constipation, better energy, improved fullness and satisfaction after meals, and even support for immune health and mood.
How do prebiotics and probiotics work together to support a healthy gut microbiome, and why does that balance matter?
Prebiotics and probiotics work as a team, and I think that’s one of the easiest ways to understand them. Probiotics are the live beneficial bacteria, while prebiotics are essentially the food that helps those beneficial bacteria grow and thrive. So you can think of it like this: Probiotics are the seeds, and prebiotics are the fertilizer. You really need both for a healthy gut environment. A lot of people focus only on probiotics, like yogurt, kefir, kimchi, or supplements, but if you’re not regularly eating enough fiber-rich foods to nourish those bacteria, they may not be able to stick around or function as effectively. That’s where prebiotic foods like beans, oats, garlic, onions, bananas, asparagus, and many fruits and vegetables come in. It’s also why I encourage people to focus less on finding one “perfect” probiotic supplement and more on building overall dietary patterns that support the microbiome long term. A diverse, fiber-rich diet paired with fermented foods can often do more for gut health than relying on one product alone.
What are some healthy lifestyle habits that naturally support prebiotic and probiotic intake and overall digestive health?
One of the biggest is simply eating enough fiber — and not just more fiber, but a variety of fiber-rich foods. Different plant foods contain different types of fibers that nourish different beneficial gut bacteria. I also encourage including fermented foods when possible, because they can provide beneficial live bacteria. Hydration is another huge piece that people underestimate. Fiber and fluids work together, especially for regular digestion and stool consistency. Movement matters, too. Regular physical activity has actually been associated with positive changes in the gut microbiome and can help support motility and digestion. Then there are the habits people don’t immediately connect to gut health: sleep and stress management. The gut and brain are closely connected through the gut-brain axis, so chronic stress and poor sleep can absolutely impact digestion, appetite, bowel habits, and even the gut microbiome itself.
What do most people get wrong about gut health, especially when it comes to prebiotics and probiotics? Is there a misconception you see come up most often?
One of the biggest misconceptions I see is the idea that gut health comes from one product — whether that’s a probiotic supplement, greens powder, detox, or “gut healing” trend on social media. In reality, gut health is usually much less glamorous and much more foundational. Your gut microbiome is influenced by your overall lifestyle and dietary patterns over time, not one quick fix.
I also think people tend to over-focus on probiotics while underestimating prebiotics. Probiotics get most of the attention because they’re marketed heavily, but beneficial bacteria still need to be nourished to survive and function well. That’s where prebiotic-rich foods like beans, oats, fruits, vegetables, garlic, onions, and whole grains become so important.
Another misconception is that if a food causes temporary bloating, it automatically means it’s bad for your gut. Sometimes increasing fiber intake too quickly or introducing more prebiotic foods can cause temporary digestive changes, especially if someone’s diet was previously very low in fiber. That doesn’t necessarily mean the food is harmful. Often, it means the gut is adapting.
