If you feel like you catch just about every cold that runs through your office, you may want to take a look at what you’re eating.

People who keep getting sick are often lacking in one particular nutrient, registered dietitian Grace Derocha tells TODAY.com.

You might assume you need more vitamin C and zinc to keep your immune system happy, but there’s another immunity-boosting nutrient that gets forgotten far too often, Derocha says.

Dietitian Tip of the Day: If You Keep Getting Sick, Eat More Fiber

“If I notice people are sick all the time, one of the things I say to them is: Are you getting enough fiber?” Derocha explains. “And 99% of the time, the answer is no.”

In fact, most adults in the U.S. do not meet the recommended 25-38 grams of fiber every day.

But foods that are rich in fiber include fruits, vegetables, legumes and whole grains — all of which contain nutrients that support your immune function and overall health.

Why It Matters

For anyone who wants to restore their microbiome or just have better gut health, fiber is essential, Derocha says.

Fiber keeps food moving through your digestive system properly. And some forms of fiber are actually prebiotic, meaning they feed the good gut bacteria in your body.

That has important effects on your immune system as well. “We know that gut-brain axis is there,” Derocha says, “and we know that a lot of our immunity and our immune system lies in the gut.”

About 80% of your immune cells live in your gut, dietitians told TODAY.com previously. So keeping your gut microbiome balanced and happy will also help ensure your immune system is functioning properly.

Of course, it’s not just the fiber that helps keep you feeling good. “Fibrous foods are fruits, veggies, whole grains,” Derocha says. These are foods that are naturally packed with nutrients, like vitamins, minerals and antioxidants that help boost your overall health in many ways.

Foods like strawberries, bell peppers and citrus contain fiber and are rich in vitamin C, for instance. Meanwhile, chickpeas, oats, almonds and pumpkin seeds are packed with both fiber and zinc.

How to Get Started

If you want to get more fiber in your day, start by adding about 5 grams at a time, Derocha recommended previously. That’s the equivalent of one apple or pear a day, or a handful of almonds or dried figs.

And Derocha previously told TODAY.com that one of her favorite ways to get more fiber is chia pudding topped with whatever fresh fruit she’s excited about at the moment.

This is a great make-ahead option that can be customized for breakfast, a snack or even dessert, she says. Chia seeds are naturally packed with fiber, plant-based protein and heart-healthy omega-3 fatty acids.

TODAY’s Expert Tip of the Day series is all about simple strategies to make life a little easier. Every Monday through Friday, different qualified experts share their best advice on diet, fitness, heart health, mental wellness and more.