What’s the Difference Between Fiber, FODMAPs, and Prebiotics?

Science is just beginning to understand the importance of good gut health—and it's already a hot topic among health professionals. But in order to figure out what's best for you, it's necessary to understand the difference between some of the more complicated (but necessary) lingo: fiber, FODMAPs, and prebiotics.

Fiber, FODMAPs, and prebiotics all promote gut health and feed those beneficial microbes that reside in our colon. Although some foods may contain all three elements, (fiber, FODMAPs and prebiotics) these terms do not refer to the same thing. Let’s break it down.

Fiber is any non-digestible carbohydrate present in plant foods such as whole grains, legumes, vegetables, fruits, nuts, and seeds. Dietary fiber escapes digestion in the upper gastrointestfodminal (GI) tract but may be degraded and consumed by the microbes that live in our large intestine.

If a fiber can be used as a food source for our healthy gut microbiota, it qualifies as prebiotic. Some fiber cannot be consumed even by gut microbes. But it still offers other health benefits such as alleviating constipation, keeping blood sugar in check, and improving mineral absorption.

Unfortunately, most of us are not eating enough fiber. According to the Institute of Medicine, we should aim for about 25-38 grams per day, and most Americans eat less than half of that.

However, adding fiber too quickly to one's diet may cause gas, bloating, and abdominal symptoms, so it's important to adjust your fiber intake gradually along with adequate water, until you meet your fiber goal. Plant foods that are ultra-processed tend to have less fiber such as white bread, pasta, and juices, versus whole grain pasta, breads and whole fruits. An apple has about 4 ½ grams of fiber while a cup of apple juice has zero.

Prebiotics, like fiber, are not digested in the human GI tract but are consumed or acted upon by our gut microbes to produce beneficial effects for human health. Although most prebiotics are fiber, there are some non-fiber prebiotics including polyphenols (chemicals found in plants that provide the plant color and often act as antioxidants) and lactulose (a non-absorbable sugar).

The health benefits of prebiotics include helping maintain healthy cholesterol levels, regulating the immune system, reducing risk of constipation, and enhancing absorption of minerals, to name a few.

Prebiotics by definition feed beneficial gut microbes (i.e. “the healthy bacteria”). There is no specific daily recommended amount of prebiotics but the research suggests that most people should try to consume more than they are currently eating. Common prebiotic rich foods are onion, leeks, wheat, garlic, oats, artichoke, unripe banana, beans, and cooked then cooled potato (as in a potato salad).

FODMAP is an acronym referring to Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols, a group of commonly malabsorbed carbohydrates including some sugars and some fiber—in fact, a popular anti-bloating diet aims to help people avoid FODMAP-rich foods.  

FODMAP sugars include lactose and fructose, fiber (oligosaccharides) and sugar alcohols (sorbitol and mannitol). The oligosaccharides contain prebiotic fiber. There are two primary prebiotic fiber in this so called “O” group: Fructans (found in garlic, onion, wheat) and galacto-oligosaccharides (found in legumes). In short, a diet that reduces FODMAP carbohydrates will restrict intake of some prebiotic fiber.

FODMAPs by nature, are small size carbohydrates and their size allows for rapid consumption by gut microbes. Think of FODMAP fiber as “fast food” for our gut microbes!

In a nutshell, the FODMAP diet is a 3 phase science-based nutritional intervention used to manage digestive symptoms for people with irritable bowel syndrome, gas, bloating, or abdominal pain. The low FODMAP diet has been shown to offer digestive relief in about 50-75 percent of individuals with IBS.

When it comes to diet: One size does not fit all

To complicate things, prebiotics appear to work differently for different people. For example, one person may consume a prebiotic rich food and this is acted upon by a specific microbe in their gut which offers a specific health benefit. Another person may have a similar microbe that eats the prebiotic, but their intestinal bacterial may not make the same healthy end product.

It’s an individual process as we all have our very own unique "fingerprint" of microbes. This is an area of science that needs much more research, remains quite new and continues to evolve.

Bottom line: Fiber and prebiotics offer a number of health benefits such as helping people maintain normal bathroom habits; regulate satiety, blood sugar, and our immune system. Most of us would benefit from increasing our consumption until we meet the recommended fiber intake.

Some fiber rich foods may also function as prebiotics, but not all. And some may be a source of FODMAP gastrointestinal issues, but not all. For the majority of people without irritable bowel syndrome, we recommend consuming a variety of fiber-rich foods, including foods with FODMAP fiber (prebiotics), to keep your gut microbes well fed and gut health in check.

For those with IBS, reducing FODMAP carbohydrates may leads to improvement in GI distress. In that instance, try incorporating other non-FODMAP fiber and prebiotics such as oats (raw and cooked), and unripe bananas, among others, allow as many tolerable prebiotic foods back into your diet.

---

Kate Scarlata is a Boston-based registered and licensed dietitian as well as a New York Times best selling author with 25+ years of experience. Kate specializes in the low FODMAP diet and digestive health conditions including: IBS, celiac disease, inflammatory bowel disease, and small intestinal bacterial overgrowth (SIBO).