Americans are obsessed with protein. Protein bars and shakes are just the beginning; there are also all those protein-fortified staples like cereals, breads, and pancake mixes dotting grocery store shelves. It seems like everyone is tracking their protein intake as the biggest health imperative.

But as protein gets all the attention, there’s another nutrient that’s sorely lacking from most of our plates: fiber. What is fiber, and why are we falling short of the recommended daily intake? (A whopping 95 percent of Americans are failing to get enough fiber, 22-34 grams for adults.) We spoke with experts to learn why fiber is so important and how we can increase fiber intake in our diet.

Fiber is a type of carbohydrate that doesn’t get digested by our bodies. Instead, it moves through the digestive system, helping maintain regularity, promoting a healthy gut, and stabilizing blood sugar levels. You can think of fiber as the janitor of your digestive system, says Dr. Omar Khokar, MD, a gastroenterologist who specializes in digestive cancer screenings. "It sweeps things through, keeps inflammation at bay, and feeds the good gut bacteria. Without it, things get backed up."

And while fiber doesn’t get absorbed by our bodies, it does get absorbed by our “good” gut bacteria that use it as fuel. “Your gut bacteria turn fiber into compounds that lower inflammation and support immunity, so make sure you’re feeding your microbiome,” Dr. Khokar adds. 

Fiber comes in two different types, soluble and insoluble in water, and each has distinct health benefits. You’ll find soluble fibers in fruits and vegetables, while insoluble fibers usually come from cereals and grains.

The root of the problem lies in our modern lifestyle, says registered dietitian Lauren Manaker. "Many people prioritize convenience foods over cooking at home, and those ultra-processed options tend to be low in fiber." That includes everything from that frozen dinner you picked up at the grocery store to the fast-food lunch you grabbed at the drive-thru. Eating these options means we often miss out on whole foods, such as fruits and vegetables in their purest form, whole grains, legumes, and nuts—basically, all the key sources of fiber.

What happens if you don’t get enough fiber? According to Dr. Khokar, there’s a lot more at stake than just your digestive health. "Constipation is the obvious issue caused by lack of fiber, but it doesn't stop there. A low-fiber diet is linked to higher risks of colon cancer, heart disease, type 2 diabetes, and even depression. The gut isn't just plumbing, it’s your second brain." 

On the flip side, a fiber-rich diet may improve digestion, support healthy cholesterol levels, help control blood sugar, and reduce your risk of serious chronic diseases, says Manaker.

There are some hard-to-miss signs you’re not consuming enough fiber. "If you’re not pooping regularly, or your stools are hard, small, or leave you feeling like you’re not quite done, fiber might be the missing link," says Dr. Khokar. But things might also be less obvious. "Weirdly enough, fatigue, bloating, or even skin breakouts can be signs your gut microbiome isn’t happy—and that often comes back to fiber."

So how can you make sure you’re eating enough fiber? Manaker recommends aiming for at least five servings of fruits and vegetables per day, and combining them with whole grains, nuts, and legumes. Dr. Khokar puts it simply: “Aim for 30 grams of fiber a day. And if it doesn’t rot or expire quickly, it probably doesn’t have fiber." 

Both experts agree that getting your fiber from whole foods is best. “Whole foods like fruits, vegetables, whole grains, nuts, and legumes provide more than just fiber; they’re a source of vitamins, minerals, antioxidants, and other nutrients that contribute to overall health,” says Manaker. 

To help you visualize how to get to about 30 grams of fiber a day (aka the ideal intake), here’s how much fiber is in some of the most commonly consumed whole foods. (You can also search USDA's FoodData Central for the fiber content of other foods.)

1 cup cooked lentils	15 grams
1 avocado	13 grams
1 cup fresh raspberries	8 grams
1 cup baked sweet potato cubes	6.6 grams
1 cup cooked broccoli	5 grams
1 apple	4.5 grams
1 cooked oats	4 grams
1 banana	3 grams

While fiber supplements can help in certain situations, they lack the comprehensive nutritional value that whole, fiber-rich foods provide—Manaker advises against relying on them for your fiber intake.