Q&A: How does processed fiber impact human health?

UNIVERSITY PARK, Pa. — The rate of Americans diagnosed with digestive disorders and gastrointestinal cancers is rising, especially in those ages 50 and younger, so researchers in the Penn State Department of Nutritional Sciences are studying how processed food additives affect humans’ gastrointestinal health.

One such additive is processed dietary fiber, which is extracted from natural sources and chemically modified for use in foods. It is used in a variety of processed foods — including bakery items, yogurt, ice cream and soda — to improve flavor, texture and appearance to make them more appealing for consumers.

Some companies market the health benefits of processed fibers in their nutrition supplements and fortified food products, the process of adding nutrients not naturally present or in higher amounts. However, these marketing claims may not be accurate, according to Vishal Singh, associate professor of nutritional physiology and microbiome.

“Every time I see any advertisement, food product or supplement in a store that markets fiber content, I feel this urgency to better understand how these processed fibers are impacting our health,” Singh said. “We, as a field, do not know much about the long-term effects of these refined, isolated fiber products, but they are so widely available. Also, people are using them without knowing if there are any risks to consuming them long term.”

Singh, who leads the Nutrition and Microbiome – Singh Lab, studies how different processed fibers impact intestinal and liver health. The lab uses pre-clinical animal models to investigate how these fibers impact digestive health in both healthy individuals and those with chronic inflammatory conditions, such as inflammatory bowel disease (IBD) and colon cancer. In this Q&A, he discussed what his research has revealed about different processed fibers and how they affect the digestive system.

Q: How are processed fibers different from natural fibers?

Singh: There are a few different types of isolated and chemically modified fibers that you can find in processed foods and supplements. By employing pre-clinical models, my lab has been primarily investigating inulin, guar gum and partially hydrolyzed guar gum (PHGG) and how these processed fibers affect metabolic, liver and intestinal health.

While these fibers are derived from natural sources, they are not always used in their original form. For example, cluster beans are rich in guar gum, but in their natural state, they also contain other types of fibers in addition to guar gum. After extraction, guar gum — known for its thick consistency and difficulty in blending with other ingredients — is treated with enzymes to break down its long-chain fibers into shorter ones. This enzymatic treatment improves its solubility and functionality, making it easier to incorporate into various processed foods and beverages.

Everyone needs fiber to maintain optimal gut and digestive health, yet most people fall short of their daily recommended intake. It's easy to see why many turn to supplements or processed foods labeled 'high fiber' as a quick fix. However, relying heavily on these isolated, chemically modified fibers raises a significant question: What are the long-term health consequences of consuming them in large quantities? That is precisely the critical, unanswered question my lab is working to solve.

Q: Does it matter which type of fiber, natural or processed, we eat?

Singh: When we eat fiber from a whole food source, we consume a mixture of different types of fibers rather than an isolated type of fiber, as seen in processed foods. In processed foods with added fiber and fiber supplements, you are consuming a much larger quantity of single types of fiber than you would from a natural source. A banana, for instance, contains multiple types of fiber, including a relatively small amount of inulin compared to other fiber types, such as pectin and hemicellulose, along with other beneficial nutrients.

Consuming a variety of fiber types is important to the digestive process, such as breaking down complex foods, maintaining healthy bowel movements, balancing blood sugar and promoting good gut health. If we only consume a single source of fiber, we will miss key components that contribute to healthy digestion and disrupt the gut’s microbiome.

The gut microbiome, a vast community of trillions of microorganisms — mostly bacteria — residing in our lower digestive tract, is key to understanding the impact of processed fibers on digestive health. Similar to how table sugar is easily metabolized by humans, these powdered fibers are highly accessible nutrients for the bacteria living in our gut. However, their rapid fermentation tends to promote imbalanced bacterial overgrowth. For instance, in one of our experimental studies, we observed that this undesirable overgrowth of a specific group of bacteria, triggered by excessive inulin — a type of complex sugar — intake, led to the accumulation of non-beneficial microbial metabolites in the specific areas of the digestive system. This accumulation potentially contributes to and worsens health issues such as IBD and colon cancer.

Q: Are there certain people who should limit how much processed fiber they eat?

Singh: Those with digestive conditions, like IBD or irritable bowel syndrome (IBS), and those with cancers related to the digestive system should try to avoid consuming processed fibers. The microbiomes of individuals with these conditions may not handle processed fibers in a beneficial way. They tend to experience negative effects, such as worsening of their conditions and other digestive-related issues like abdominal pain, bloating and diarrhea. Research on this topic is still in its early stages, so we have a lot more to learn about how processed fiber affects individuals with existing digestive issues.

Most studies investigating the effects of processed fiber include healthy participants, rather than those with preexisting conditions, such as IBD. This was one of the reasons we started our recent study on PHGG, to at least learn from the pre-clinical models whether these refined fibers will be beneficial in some respects or not.

Q: How should people get fiber in their diet?

Singh: While our recent findings were derived from pre-clinical models, we found that relying on a single source of fiber may not be beneficial for long-term intestinal and liver health. If someone wants to increase their fiber intake, instead of relying on a fiber supplement that is a high dose of a single type of fiber, we recommend including a variety of fruits, vegetables and whole grains to help get the different types of necessary fibers, as well as the other essential nutrients. Whole foods provide multiple types of fiber that support the growth of diverse microbes in our gut, fostering microbial diversity, which is beneficial for overall health.