Soluble and insoluble fiber are carbohydrates that your body doesn’t digest.
Soluble fiber dissolves in water to form a gel-like substance. It’s especially helpful for managing blood sugars and cholesterol.
Insoluble fiber doesn’t dissolve in water, so it moves through your digestive tract intact. It’s great for preventing or relieving constipation.
It’s important to eat a variety of fiber-rich foods with a blend of soluble and insoluble fiber throughout the day.
Soluble Fiber
Soluble fiber pulls water into your digestive tract, forming a gel-like substance. It slows digestion, allowing your body to absorb more nutrients as it passes through your system. This is especially helpful for managing diarrhea and preventing blood sugar spikes.
Soluble fiber is also helpful for lowering your cholesterol. It binds with cholesterol during digestion so your body can excrete it in your poop.
Studies show that the microorganisms—things like bacteria, viruses, and fungi—in your gut can easily access and metabolize soluble fiber. The process mainly produces short-chain fatty acids, which may have various health benefits, including improved gut health.
Here are some specific benefits of soluble fiber:
- Feeds healthy bacteria in the gut
- Promotes satiety
- Prevents blood sugar spikes
- Lowers cholesterol
- Improves nutrient absorption
- Prevents gut inflammation
You can get soluble fiber from foods like oats, beans, apples, bananas, and avocados.
Insoluble Fiber
Insoluble fiber, on the other hand, does not dissolve in water. It moves through your system whole, adding bulk to your stool and speeding up digestion. This helps you poop, especially if you struggle with constipation.
Insoluble fiber can also improve insulin sensitivity, helping to balance your blood sugar. It’s found in whole grains, nuts, seeds, and the skins of most fruits and vegetables.
The benefits of insoluble fiber include:
- Improves insulin sensitivity
- Lowers the risk of type 2 diabetes
- Lowers the risk of high blood pressure
- Prevents and relieves constipation
Shopping for a fiber supplement can be overwhelming. Interestingly, most fiber supplements have soluble fiber.
Soluble Fiber Supplements
Most fiber supplements out there contain soluble fiber:
- Psyllium powder: This comes from psyllium husk, and it’s what you’ll find in Metamucil. It helps add bulk to the stool and can effectively lower cholesterol. However, it doesn’t get fermented for prebiotic benefits.
- Inulin: Inulin, which comes from chicory root, is considered a non-viscous soluble fiber. It doesn’t have the same cholesterol-lowering benefits as other types of soluble fiber. It could still be a valuable way to up your total fiber intake and relieve constipation. Plus, it gets fermented in your large intestine for prebiotic benefits.
- Guar gum: Guar gum can help lower cholesterol since it forms a gel-like substance as it moves through your system. Plus, your large intestine ferments it for gut health benefits. However, it probably won’t help with constipation or diarrhea.
- Beta-glucan: This is found naturally in foods like oats and some mushrooms, but you can also get it as a supplement. It can help lower cholesterol and blood sugars to prevent heart disease and diabetes.
- Methylcellulose: You can find this type of fiber in Citrucel. It doesn’t get fermented by your large intestine, but it is viscous, so it can help you manage high cholesterol and blood sugars.
- Wheat dextrin: This type of fiber is found in the popular fiber supplement Benefiber. It’s not fermented, so it won’t act as a prebiotic. However, it can help soften stool to make it easier to pass.
Insoluble Fiber Supplements
The main insoluble fiber supplement is called cellulose. Here’s what to know about it:
- Cellulose: This supplement works as a stool softener, making poop easier to pass. It isn’t shown to lower cholesterol or improve blood sugars.
Taking a fiber supplement or eating too much fiber could cause symptoms like gas, bloating, constipation, or diarrhea. The risk of unpleasant symptoms is higher if you increase your fiber intake too quickly or if you don’t drink enough fluids. As you eat more fiber, you need to drink more fluids since fiber draws in water as it moves through your system.
If you have a digestive disorder like irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD), eating certain types of fiber may worsen symptoms. For example, studies show that highly fermentable fiber can worsen IBS symptoms, but moderately fermentable fiber can help. Psyllium, in particular, is recommended for IBS. Increase your intake by no more than 5 grams per day each week.
It’s generally best to consult with a trusted healthcare provider before starting a fiber supplement, especially if you have a gastrointestinal illness.
Most adults need 25–38 grams of total fiber per day, but U.S. adults average only 16 grams per day. Most people could stand to eat more fiber to meet the recommended intake. That said, it is possible to eat too much fiber.
There’s no official upper limit for fiber intake, but be careful about eating way more than the recommended daily intake. Increasing your fiber intake too quickly can lead to uncomfortable gastrointestinal symptoms like gas or bloating, so it’s best to add more fiber gradually.
If you have Crohn’s disease, an intestinal blockage, recent bowel surgery, or malabsorption issues, you may even need to limit your fiber intake. In that case, it’s best to talk with your healthcare provider or registered dietitian about how much fiber is safe for you to consume.
Soluble and insoluble fiber are essential for overall health. Soluble fiber gets fermented by your gut bacteria to benefit gut health. It can also help lower cholesterol, prevent blood sugar spikes, and relieve diarrhea. Insoluble fiber moves through your digestive tract whole. It’s great for relieving constipation and reducing your risk of type 2 diabetes.
You need both of them for overall health. To get more fiber, incorporate a variety of fruits, vegetables, nuts, seeds, legumes, and whole grains into your diet.
