All About Fiber: Why You Need It, the Top Sources, and What Happens if You Eat Too Much

Eat more fiber. We’ve all heard this advice, so we assume it must be good for us. The problem is that fiber and flavor might seem like opposites — and for many of us, flavor is the typical driver of food choice. But the reality is that fiber can have flavor, along with medicinal effects to potentially help reduce and prevent common diseases. In this article, let’s take a look at exactly what fiber is and how it functions in the body.

What Is Fiber Exactly, and Generally, What Foods Contain This Carb?

Fiber is simply a type ofcarbohydratefound naturally in plant-based foods that is not digestible in humans.

Plant-basedfoods that are rich in fiber— such as fruits, vegetables, whole grains, beans and legumes, and nuts and seeds, liststhe U.S. Department of Agriculture'sMyPlateguidelines— also contain vitamins, minerals, and other powerful nutrients that the body can use for optimal health.

Although fiber cannot be digested, it is being moved down the digestive tract as nutrients are being digested, and can do some great things that positively impact our health.

The problem is that Americans are getting less than half of the daily intake recommendations of 14 grams (g) for every 1,000 calories of food. (1,2)

A simpler recommendation level for most adults is between 25 and 38 g per day (1). In fact, fiber is listed as a “nutrient of concern” due to the low overall intake and known health benefits. (3)

There are two types of fiber: soluble and insoluble. While both are important, the two function differently in the body. Here’s how:

Soluble Fiber

Soluble fiber is a type of fiber that attracts water and forms a gel. This gel causes a slowing of the digestion process, which can be beneficial for weight loss. Foods high in soluble fiber include oats, legumes, edible plant skins, and nuts. (4)

Insoluble Fiber

Insoluble fiberis the type of fiber that, you guessed it, repels water. You can find insoluble fiber in foods such as veggies, fruits, nuts and seeds, wheat bran, and whole-grain foods like whole-wheat pasta and brown rice. Its primary benefit is to provide bulk to stool and aid in the movement through the digestive tract. (4)

Most diets have a combination of soluble and insoluble fiber, with 75 percent coming from insoluble fiber and 25 percent coming from soluble fiber. (5)

In short, fiber may actually help you live longer. (6) Studies suggest folks who eat a higher intake of fiber tend to have lower rates of heart disease, obesity, type 2 diabetes, stroke,high blood pressure (hypertension), and digestive diseases. (7)

You may help improve or prevent health conditions such asprediabetes, diabetes,high cholesterol, obesity, and various digestion problems, likeconstipation, colon cancer, and diverticulitis,by simply increasing fiber in your diet. (8,9)

Weight Loss

Research suggests nutrients like fiber can play a major role in body weight. (10) Normal-weight and overweight people have been found to have higher intake of dietary fiber than obese individuals. (8) Other studies continue to suggest that high fiber intakes help reduce weight gain as you age. (7)

Fiber expands and bulks food in your GI tract, slowing digestion. This can increase satisfaction of your food andhelps stabilize blood sugar levels. (4)Foods high in fiberalso tend to be lower in energy density, meaning they’ll help you feel fuller without consuming excessive calories. (4) This concept is at the core of why a higher fiber diet is associated with a lower rate of obesity. (11)

Digestive Disorders

Fiber is like nature’s scrub brush, keeping your body’s pipes clear and reducing carcinogenic activity.

One benefit of getting enough fiber in your diet is reducing therisk of diverticulitis, a condition in which pouches formed in the colon become infected. Fiber helps keep food clear from the pouches and moving through the digestive tract. Aim to take in 25 to 40 g of fiber per day to reduce your risk of diverticulitis. (12)

There’s an anti-cancer benefit to fiber, too: Both soluble and insoluble fiber can also play a role in warding off colon cancer. (13)

Cholesterol and Blood Pressure Reduction

Fiber’s wondrous effect on the body is a great example of medical nutrition therapy (MNT), a technique registered dietitian nutritionists (RDN) use on their patients to reduce the need for medication while improving health outcomes.

Here’s how it works: Your body uses bile salts, which are excreted by thegallbladderto break apart the fat content in food. Bile salts are made of cholesterol.

When you eat food with fiber, the fiber binds to the bile salts, preventing them from being recirculated for the next time you eat. As a result, your body must produce more bile salts by taking cholesterol from the liver. This is how soluble fiber reduces blood cholesterol. (14)

Fiber has a preventative role on blood pressure, too, but the reason is more associated with nutrients such aspotassium, calcium, and magnesium contained in foods high in fiber. (11)

If you are not convinced to increase your fiber intake yet, know there’s also data emerging on fiber’s ability to impact the immune system, mood, and memory by the promotion of healthy gut bacteria. (15)

The Food and Drug Administration (FDA) has established a daily value for foods and supplements with food labels. The daily value (DV) for fiber is 25 g. (4)

Note that natural foods containing fiber typically have a combination of soluble and insoluble fiber with the majority coming from soluble fiber. To lower your blood cholesterol by 3 to 5 percent, aim to take in at least 5 to 10 g of soluble fiber per day. (16)

Here are some food sources of fiber, along with how much of the DV of fiber they offer: (17)

Fruit

• Passion fruit (1 cup): 25g, 100 percent
• Breadfruit (1 cup): 11g, 44 percent
• Raspberries (1 cup): 8g, 32 percent
• Blackberries (1 cup): 8g, 32 percent
• Boysenberries and gooseberries (1 cup): 7g, 28 percent
• Pear (1 medium): 6g, 24 percent
• Prunes (5 pieces): 3g, 12 percent

Vegetables

• Artichoke (1 large): 9g, 36 percent
• Lima beans (1 cup): 9g, 36 percent
• Green peas (1 cup): 8g, 32 percent
• Lentils (½cup): 8g, 32 percent
• Kidney beans (½cup): 6g, 24 percent
• Sweet potato (½cup, mashed): 4g, 16 percent

Nuts and Seeds

• Chia seeds(1 ounce (oz)): 10g, 40 percent
• Flaxseeds (1 oz): 6g, 40 percent
• Pumpkin seeds (1oz): 5g, 20 percent
• Almonds(1 oz): 4g, 16 percent

Grains

• Raisin Bran (1 cup): 7g, 28 percent
• 小麦片(2饼干):6克,24%
• Oat bran (1 cup): 6g, 24 percent
• Brown rice (1 cup): 4g, 16 percent

Just as with everything else in life, gettingtoo much fibercan be harmful to your health. The U.S. Dietary Guidelines hasn’t established an upper limit on fiber intake, but it’s well known that eating too much fiber can cause gas,bloating, and diarrhea. (18) A sudden increase in fiber, inadequate fluid intake, and inactivity, along with a high-fiber diet, may increase the likeliness of these symptoms.

When you take in more than 50 g of fiber per day, you may also face a risk of mineral binding, which essentially means your body excretes them instead of absorbing them. Some of the minerals at risk of binding with excess fiber intake includecalcium, magnesium, and phosphorus. (19)

Doctors often prescribe fiber supplements for thetreatment of irritable bowel syndromeor constipation. These supplements are considered functional fibers that are isolated from plant sources:

• Metamucil (psyllium)is a type of soluble fiber supplement you can use to bulk stool and encourage regular bowel movements.
• Dextrin is a type of soluble, prebiotic fiber found in products such asBenefiberthat promotes good bacteria for overalldigestive health.
• Citracel (methylcellulose)andFibercon (polycarbophil)are other fiber supplement options to help keep you regular.

Whole-wheat food products, like brown rice, whole-grain bread, and whole-grain pasta, are a quick and easy source of fiber in many parts of the world. But these foods contain the binding protein谷蛋白, and if you have the autoimmune conditionceliac disease, or a wheat allergy, you need to avoid these types of foods to prevent serious health issues. (20,21)

Even if you don’t have one of these ailments, you may find that eating wheat causes gas, bloating, andabdominal pain. (22) If you and your doctor determine giving up whole wheat is best for you, you’ll need to add other whole grains to your diet in its place, as avoiding wheat can lead to a fiber deficiency.

If you have a wheat allergy, a gluten intolerance, or celiac disease, consider eating high-fiber gluten-free grains, like millet, amaranth,quinoa, and buckwheat. Gluten-free oats are also an option. (21)

Although dextrins are derived from wheat, dextrin supplements meet the FDA’s guidelines for gluten-free of less than 20 parts per million. (23)

Bottom line: You’re likely not getting enough fiber, so consider eating more. The best way to get fiber is through natural sources, such as fruits, vegetables, whole grains, nuts, seeds, and legumes, because these sources also include important vitamins, minerals, and phytonutrients your body needs for optimal health.

Ask your doctor or RDN if a fiber supplement would be right for you if you are trying to treat or prevent a health condition. Don’t have an RDN?You can find one at EatRight.org.