Soluble fiber doesn't sound like something you'd want to eat, but it's in plenty of the foods you know and love, like avocados, sweet potatoes and black beans, to name a few. Both soluble and insoluble fiber are crucial for healthy digestion, weight loss and the prevention of certain cancers. Soluble fiber also has some specific benefits that will make you want to eat more of the foods that contain it.
Avocados, figs, oats, carrots, sunflower seeds, beans and potatoes are high in soluble fiber.
What Is Soluble Fiber?
There are two kinds of fiber: soluble and insoluble fiber. Insoluble fiber, including cellulose and hemicellulose, according to Healthline, remains mostly intact in the stomach and intestines. It increases stool bulk and aids the movement of food through the digestive system. Soluble fiber, including plant pectin and gums, dissolves when it comes into contact with digestive fluids, forming a gel-like substance.
Best Sources of Soluble Fiber
Most plant foods contain some soluble fiber but in varying amounts. According to Dietitians of Canada, beans, peas and oat products are the richest soluble fiber foods. Some examples of foods highest in soluble fiber include:
- Black beans: 5.4 grams in 3/4 cup
- Lima beans: 5.3 grams 3/4 cup
- Soy nuts: 3.5 grams in 1/4 cup
- Navy beans: 3.3 grams in 3/4 cups
- Pinto beans: 3.2 grams in 3/4 cup
- Purple passion fruit: 6.5 grams in 1/2 cup
- Oat bran: 2.2 grams in 3/4 cup, cooked
- Oatmeal: 1.4 grams in 3/4 cup, cooked
- Avocado: 2.1 grams in 1/2 fruit
- Brussels sprouts: 2 grams in 1/2 cup, cooked
- Dried figs: 1.9 grams in 1/4 cup
- Oranges: 1.8 grams in one medium fruit
- Sweet potato: 1.8 grams in 1/2 cup, cooked, without skin
- Asparagus: 1.7 grams in 1/2 cup, cooked
- Turnips: 1.7 grams in 1/2 cup, cooked
- Broccoli: 1.2-1.5 grams per 1/3 cup, cooked
- Apricots: 1.4 grams in three fruits with skin
- Nectarines: 1.4 grams in one medium fruit
Health Benefits of Soluble Fiber
Like insoluble fiber, soluble fiber also increases stool bulk and helps the passage of materials through the digestive system. But its unique structure has more far-reaching health benefits. These include benefits for heart health, weight maintenance, blood glucose control and gut health.
Improves Heart Health
As it moves through the digestive tract, soluble fiber attracts not only fluids, but also other wastes and cholesterol and helps carry them out of the body, according to WebMD. Specifically, soluble fiber helps lower blood levels of the "bad" cholesterol, called low-density lipoprotein, or LDL.
LDL cholesterol is a waxy, fatty substance that can build up in your arteries and lead to atherosclerosis, which is a narrowing and hardening of the arteries that blocks blood flow to the heart and other parts of the body, according to the National Heart, Lung and Blood Institute. This can eventually lead to heart attack, stroke and heart disease.
Lowers Blood Pressure
Soluble fiber can also improve heart health by helping to lower blood pressure. High blood pressure occurs when the force of blood flowing through your blood vessels is too strong on a regular basis. According to the American Heart Association, almost half of all adults have high blood pressure.
In a systematic review and meta-analysis of randomized controlled trials published in Nutrition, Metabolism and Cardiovascular Diseases in 2018, researchers found that soluble fiber supplementation reduced systolic and diastolic blood pressure. The researchers concluded that adding soluble fiber to the diet could be valuable for reducing the risk of cardiovascular disease.
Did you know? Systolic blood pressure is the first number and diastolic blood pressure is the second number. Both numbers are important and can be used to diagnose high blood pressure; however, systolic blood pressure may play a larger role in heart disease risk. According to the Centers for Disease Control and Prevention, a healthy blood pressure level is less than 120/80 mmHg.
Protects Against Diabetes
People with diabetes have consistently high blood glucose levels. Soluble fiber slows the digestion and absorption of sugars into the bloodstream, which may help to lower blood glucose. According to Diabetes.co.uk, even a small increase in soluble fiber intake is beneficial for people with diabetes. It may also be effective to lower the risk of developing diabetes.
In a 2016 study in Experimental and Therapeutic Medicine, researchers divided study participants with Type 2 diabetes into two groups. One group received 10 or 20 grams of soluble fiber each day, and the other group received no soluble fiber.
After one month, the researchers found that the group receiving 20 grams of soluble fiber had significantly improved fasting blood glucose levels, as well as markedly improved insulin resistance index. The group also had significantly improved levels of LDL cholesterol.
Aids Weight Control
Both types of fiber are crucial for weight control and may even aid weight loss in the absence of dietary restriction, according to a 2018 study in Nutrition.
Because soluble fiber swells when it comes into contact with fluids in the stomach, it creates a feeling of fullness and satiety. It also slows stomach emptying, so the feeling of fullness is sustained. In addition, stomach fullness delays the release of an appetite-stimulating hormone called ghrelin, according to a review article published in 2018 in Journal of Nutrition and Metabolism.
In the 2016 Experimental and Therapeutic Medicine study, not only did the participants eating 20 grams of soluble fiber each day exhibit improved blood glucose, they also lost weight, with researchers noting significant decreases in waist and hip circumferences. And a 2017 systematic review and meta-analysis of randomized controlled trials in The American Journal of Clinical Nutrition found that in studies lasting two to 17 weeks, intake of soluble fiber led to reductions in body mass index (BMI), body fat and body weight.
Improves Gut Health
Soluble fiber is fermented in the colon by bacteria, according to Jackson Seigelbaum Gastroenterology. This fermentation fuels the growth of these healthy bacteria, which have wide-ranging effects on health, including:
- Improving immunity
- Decreasing bad bacteria
- Increasing calcium and magnesium absorption
- Strengthening bones and improving bone density
Additionally, according to a 2017 review article in Animal Nutrition, fermentation of fibers in the gut produces short-chain fatty acids (SCFAs), including acetate, butyrate and propionate. These substances have antimicrobial activity, and butyrate, specifically, is a cellular mediator in many gut cell functions including gene expression, cell differentiation, gut tissue development, immune modulation, oxidative stress reduction and diarrhea control. Furthermore, the fermentation of bacteria in the colon may lower the risk of colorectal cancer and other diseases of the colon, according to Mayo Clinic.
You can buy soluble-fiber supplements such as Metamucil, Citrucel and FiberCon. These might help to increase your fiber intake, but the Mayo Clinic says that, in general, getting your fiber from foods is the best way to go. Fiber supplements typically don't provide the different types of fiber, as well as vitamins, minerals and other nutrients, found in whole foods.
How Much You Need
There is no specific recommendation for soluble fiber, just for total fiber. According to the National Academy of Medicine, women need 25 grams of fiber each day, and men need 38 grams daily. But other organizations recommend aiming even higher than that. The Physician's Committee for Responsible Medicine, for example, recommends all adults aim for 40 grams of fiber each day.
Fitting in Soluble Fiber
Many people struggle to get enough fiber. According to UCSF Health, Americans currently get only 15 grams per day, on average. You can be sure to get all the fiber, both soluble and insoluble, by following these tips.
Eat a Fiber-Filled Breakfast
Oats and oat bran are the top soluble fiber foods and make for a hearty, filling breakfast. Top a bowl with chopped apricots or nectarines. You can also add oat bran to your regular cereal or hot cereal.
Choose Whole Grains
Refined grains, like white rice and pasta, have been stripped of their bran and germ during processing. This also strips away much of the fiber. Whole grains, as their name implies, remain whole through processing, so they retain their natural fiber content. The Dietary Guidelines for Americans, 2015-2020, recommends making at least half of the grains you eat whole grains, but more is better.
Eat More Legumes
Foods in the legumes food group, including beans, peas, lentils, soybeans and peanuts, are not only excellent sources of soluble fiber, but are also rich sources of plant protein. Unlike many types of animal protein, most legumes are low in fat and saturated fat, making them healthy substitutes for meatless meals.
Sneak in Snacks
As long as they fit within your daily calorie budget, snacks are a great way to fit in more fiber. Cut up raw veggies with hummus, nuts, fruit or even a bowl of oatmeal make for fiber-filled satisfying snacks.
Take It Slow
Increasing your fiber intake too quickly can cause stomach upset, bloating, cramping and gas, according to the Mayo Clinic. Add fiber to your diet slowly over several weeks. This gives the healthy bacteria in your gut time to get used to the change.
Also be sure to drink plenty of water. Fiber is most effective when you are well-hydrated. Soluble fiber, in particular, needs fluids to absorb so it can swell and become gel-like.
- Dietitians of Canada: Food Sources of Soluble Fibre
- Healthline: What’s the Difference Between Soluble and Insoluble Fiber?
- WebMD: Soluble and Insoluble Fiber: What’s the Difference?
- National Heart, Lung and Blood Institute: Atherosclerosis
- American Heart Association: Monitor Your Blood Pressure
- Nutrition, Metabolism and Cardiovascular Diseases: The Effect of Viscous Soluble Fiber on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
- CDC: Measuring Blood Pressure
- Diabetes.co.uk: Soluble Fibre and Diabetes
- Experimental and Therapeutic Medicine: Therapeutic Effects of Soluble Dietary Fiber Consumption on Type 2 Diabetes Mellitus
- Nutrition: A Nonrestrictive, Weight Loss Diet Focused on Fiber and Lean Protein Increase
- Journal of Nutrition and Metabolism: The Role of Fiber in Energy Balance
- The American Journal of Clinical Nutrition: Effects of Isolated Soluble Fiber Supplementation on Body Weight, Glycemia, and Insulinemia in Adults With Overweight and Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
- Jackson Seigelbaum Gastroenterology: Prebiotics
- Animal Nutrition: Implications of Butyrate and Its Derivatives for Gut Health and Animal Production
- Mayo Clinic: Dietary Fiber: Essential for a Healthy Diet
- National Academy of Medicine: Dietary Reference Intakes: Macronutrients
- Physician's Committee for Responsible Medicine: Fiber
- UCSF Health: Increasing Fiber Intake
- Health.gov: Dietary Guidelines for Americans, 2015-2020: Chapter 2. Shifts Needed to Align With Healthy Eating Patterns: Food Groups