Fiber is one of those do-it-all nutrients that most of us aren't getting enough of. Over 90% of adults in the United States do not eat enough fiber each day, despite its health benefits, according to the Dietary Guidelines for Americans.

Present mainly in plants—vegetables, fruits, whole grains, legumes, nuts and seeds—fiber is a type of carbohydrate that's primarily undigested and passes through the digestive tract. Fiber comes in two forms: soluble and insoluble, which both provide distinct benefits.

Related: 5 Easy Ways to Eat More Fiber

Most plant-based foods come with both types of fiber in varying amounts. Research shows that together, soluble and insoluble fiber form a mighty team to support a healthy gut and reduce the risk of chronic conditions, such as diabetes, heart disease and some types of cancers. Bulking up your diet with fiber has also been found to support weight loss.

It's clear that getting more fiber is a good goal. So if you want to increase your fiber intake, read on to learn about the differences between soluble and insoluble fiber and what foods contain each type of fiber. (Hint: Don't peel your apples.)

Soluble fiber is a type of fiber that absorbs water, forming a gel in the digestive tract and making stools easier to pass.

Because of its ability to absorb water and swell up, soluble fiber helps slow down the digestion of carbohydrates—and other nutrients—preventing sudden spikes in blood glucose levels. This slower digestion also help to keep you feeling fuller for longer, which is especially helpful when it comes to weight loss.

The viscous soluble fiber may lower your cholesterol level by acting like a sponge that binds to cholesterol and fat in your food, carrying them out of your body through your stools.

And that's not all: A study in the journal Nutrition, Metabolism and Cardiovascular Diseases also noted that soluble fiber might lower blood pressure. That's in part because eating foods with this fiber improves satiety, which can lead to weight loss and lower blood pressure.

If you live with irritable bowel syndrome, eating soluble fiber may help manage your symptoms, such as diarrhea and loose stools, by making your stools more dense. If you have IBS, be sure to add fiber to your diet slowly—too much, too soon may cause even more distress. And drinking enough water alongside your fiber helps, too.

You can find soluble fiber in a wide range of plant-based foods, such as:

Contrary to soluble fiber, insoluble fiber is just what it sounds like—a type of fiber that is not does not absorb water. Rather than forming a gel-like soluble fiber, insoluble fiber adds bulk to the stool and draws water to the colon, making stools soft and easy to pass.

Insoluble fiber is the tough and chewy parts of vegetables and fruits, such as apple skins, carrot peels, broccoli stems and asparagus stalks. In addition to being found in produce, you can also find insoluble fiber in whole-grain breads and cereals, wheat bran, oat bran and nuts.

There are no specific recommendations on the amount of each type of fiber you should eat each day. The most recent Dietary Guidelines for Americans recommends daily fiber intake based on age and gender. If you are pregnant, your fiber needs also change.

Generally speaking, aiming for 25 grams a day is a great goal and 30 grams or more is even better.

Enjoying a range of fiber-rich foods ensures you consume both types of fiber. Instead of meticulously tracking fiber intake, pay attention to the signs that you might be getting too much or too little fiber.

Related: 12 Foods with More Fiber Than an Apple

Symptoms of eating too much fiber include gas, bloating and abdominal cramps. On the other hand, you could become constipated, have difficulty in passing stools and develop hemorrhoids when you eat too little fiber.

In short, soluble fiber forms a gel and acts as a sponge to help get rid of fat and cholesterol, while insoluble fiber bulks up your stools. Both types of fiber are essential for supporting a healthy digestive system and overall wellness. Remember, if you're increasing your fiber intake, also increase your intake of fluids, such as plain water, to support healthy digestion.