Is eating a fiber-boosted bar or taking a fiber supplement each day just as good as eating a high-fiber diet?

Carolyn Williams, PhD, RD
November 26, 2018

Eating a higher-fiber diet is associated with a lower risk of heart disease, type 2 diabetes, and certain cancers, plus a lower body weight, greater satiety, and improved gut and digestive health. Yet it’s estimated that only about 10% of the population actually meets their daily recommended intake. This has triggered manufacturers to market more fiber-boosted foods, gummies, bars, and supplements than ever. But is reaping the benefits of a high-fiber diet as simple as hitting a daily quota of fiber grams through supplements and fortified products? I dug into the research to see if it really matters where your fiber comes from.

What Is Fiber?

Fiber is a complex carbohydrate that the body can’t digest, meaning it doesn’t contribute calories or trigger an insulin response like other carbs. Dietary fiber is what gives plants structure (such as the stalk and florets in broccoli, or the peel on an apple). All plant foods such as vegetables, fruits, grains, seeds, and nuts contain some fiber, and most all are good sources. The Adequate Intake (AI) for fiber from the Institute of Medicine is 14g per 1000 calories. Since adults need more than 1000 calories per day, the simplified and more common recommendation is 25g/day for women and 38g/day for men.

What’s the Difference Between Fibers?

In the past, fibers were classified as either “soluble” or “insoluble”, based on their ability to absorb water. But with the increase of fiber-fortified foods and supplements on the market, fibers are now also referred to as dietary or functional, based on where the fiber in a food originates. Here’s a quick look at what the classifications mean and differences.  

Soluble fibers: By absorbing water in the GI tract, soluble fibers slow the digestive process and create gels of different viscosities. It’s soluble fibers that research has linked to improvements in glycemic control and lower cholesterol.

Insoluble fibers: While they don’t absorb water, insoluble fibers play a key role in adding bulk to digestive contents. This bulk stimulates the digestive tract to regularly get rid of waste product, which is why most insoluble fibers are associated with preventing or alleviating constipation.

Dietary (intact) fibers: These are fibers that are naturally occurring in food, like the fiber that a pear or brown rice provides. Dietary fiber is made of a variety of different soluble and insoluble fibers.

Functional fibers: These are fibers used in supplements and added to foods during processing. Unlike the dietary fiber makeup in foods, functional fibers usually consist of a single, isolated type of either soluble or insoluble fiber. Foods may contain both dietary and functional fibers if functional ones are added during processing.

Does Where You Get Your Fiber From Really Matter?

Yes, and research suggests that aiming to meet fiber needs—or at least a large portion—through naturally occurring fiber in foods is ideal.

The health recommendation to eat a “higher-fiber diet” isn’t just to encourage people to hit their daily quota of fiber grams, but also to promote improvements in overall eating. When food choices focus on getting fiber, an individual typically consumes fewer calories, chooses foods that have a lower glycemic index, consumes more whole foods like fruits and vegetables (and thus more nutrients), and consumes fewer processed foods. Relying primarily on supplements or fortified foods means missing out on these things. So, while you may be getting plenty of fiber, overall diet quality hasn’t improved. Also, most research looking at health benefits is based on higher dietary or intact fiber intake, so consuming functional fibers doesn’t necessarily guarantee the same outcomes.

Fibers also have different effects based on their solubility. For example, an insoluble fiber like wheat bran helps constipation, but has little to no effect on glycemic response or heart disease; a soluble fiber such as b-glucan lowers cholesterol, but isn’t the most effective when it comes to regularity. Additionally, not all soluble and insoluble fibers are equal in effectiveness. In fact, research has linked only a handful of specific fibers as being effective when it comes to inducing certain health benefits. This means that consuming a supplement or fortified food has little effect if it doesn’t contain a specific type associated with health benefits.

When to Use Fiber-Fortified Foods and Supplements

Even though food should be first, it can be hard to hit daily recommendations, even with a diet full of produce, nuts, seeds, and grains. In this case, it’s not a bad idea to add in some fortified foods or a supplement—particularly if you have a condition like heart disease, pre-diabetes, type 2 diabetes, or a GI issue such as constipation. Because a fortified food or supplement usually only contains one or two types of fiber, the key is finding a product that contains a functional fiber to effectively address issues. To help navigate the grocery and drug store aisles, see the chart below for which fibers are associated with specific health effects, and then look for those on packaging.

Desired Health Effect

Functional Fiber(s) Associated

Alleviate or prevent constipation

Wheat bran (All Bran)

Psyllium* (Metamucil)

Reduce cholesterol levels/heart disease risk

b-glucan (oats & barley)

Psyllium* (Metamucil)

Guar gum

Increased satiety

b-glucan (oats & barley)

Psyllium* (Metamucil)

Improved glycemic control

b-glucan (oats & barley)

Psyllium* (Metamucil)

Guar Gum

Alleviating diarrhea and/or some IBS symptoms

Psyllium* (Metamucil)

Improved gut/microbiota health

In theory, fermentable fibers such as wheat dextrin (Benefiber), inulin (chicory root), guar gum and b-glucan may aid growth of good bacteria, but research has limited documentation that overall gut health is improved due to supplementation of these fermentable fibers.

*Psyllium is from the seed husks of Plantago ovata plant and may also be referred to as ispaghula on labels.

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