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Try these fiber copycats for your gut.

Reviewed by Dietitian Jessica Ball, M.S., RD

Key Points

• A group of proteins that imitate fiber may serve as fuel for your gut microbes.
• A new study suggests proteins imitating fiber may help produce beneficial metabolites.
• Proteins imitating fiber are often found in fiber-packed plant-based foods, like beans.

They say imitation is the sincerest form of flattery. When someone copies your work, behavior or style, it shows that they admire or respect you. But what if that homage wasn’t just reserved for people, but could also apply to compounds that may benefit your health?

While it may sound unbelievable, a group of proteins called “proteins imitating fiber” may do just that. These proteins, similar to fiber, can resist digestion in parts of the digestive tract and make their way to the large intestine, where they become available to gut bacteria. In that sense, they imitate one important, health-supportive function of fiber—they can provide fuel for your gut microbes. These digestion-resistant proteins can be found in a variety of foods, especially legumes. Research has identified resistant protein segments in foods such as soy beans, peas and beans; however, the amount and type of resistant protein can vary depending on the food and how it’s processed.

It’s no secret that plant-based diets rich in fiber and other beneficial compounds are associated with a number of health benefits, including benefits for gut health. Your gut microbiome is home to trillions of microorganisms, and, just like any living thing, what you feed them matters. But scientists are still working to understand exactly how different components of our diets, including dietary fiber, plant proteins and, even more recently, proteins imitating fiber, shape microbial activity and the compounds produced by our gut bacteria.

In fact, two recent studies published in PNAS and Nature Metabolismboth led by researchers out of Princeton, offer new clues. Together, the research provides a more nuanced look at how plant foods influence gut health and suggests that some proteins imitating fiber may have beneficial effects that resemble those of fiber.

How Were the Studies Conducted?

In both studies, the research teams used a technique called stable isotope tracing. Isotope tracing is a method in which researchers give a specific nutrient to an experimental cell or animal and they track it to see where it ends up and how it affects the test subject. While both studies used this method, they each set out to answer slightly different questions.

In the PNAS study, the researchers used isotope tracing to investigate what gut microbes were eating and how it affected gut health. Specifically, they were interested in understanding whether microbes were using dietary fiber or proteins. They also studied whether certain plant proteins that can resist digestion could reach the gut microbiome and act as a source of nutrients for gut bacteria. In a nutshell, they were trying to determine what gut microbes are eating and how that changes the metabolites produced.

The Nature Metabolism study also used isotope tracing to determine how metabolites—substances necessary for energy and overall health that are made or used when the body breaks down food—found in the gut microbiome are actually made. While some of these compounds are assumed to be produced by gut bacteria, researchers wanted to determine whether they were actually made by microbes, by our cells or by both. They used isotope tracing to follow different nutrients in animals and humans as they were converted into different metabolites. In other words, they were trying to determine what exactly produces metabolites.

Together, the studies used isotope tracing to highlight that what we eat can influence what fuels our microbes and allows them to produce certain metabolites.

What Did the Studies Find?

In the PNAS study, researchers found that certain plant proteins can resist digestion in parts of the digestive tract and reach the large intestine, where gut bacteria are able to use them as fuel. They dubbed these proteins “proteins imitating fiber,” or Prif, because like fiber, they are not digested and are instead made available to be used as fuel by the gut microbes. The researchers discovered that when proteins imitating fiber were paired with actual fiber, they could shift microbial metabolism in a more favorable direction—producing more beneficial metabolites.

And while those beneficial metabolites were part of the picture, researchers also took a look at where some of the less favorable metabolites produced by gut bacteria came from. They found that when the gut bacteria don’t have enough nutrients to eat, they can turn to proteins produced by the body, including proteins in the mucus that protects the intestinal lining.

In other words, when dietary fuel is scarce, gut bacteria may start looking for less ideal sources, including protein from your intestinal lining. Over time, this type of microbial activity can negatively affect the gut’s protective mucus layer. While this study doesn’t show that a low-fiber diet can directly cause poor gut health, it may offer another possible explanation for why providing gut bacteria with adequate dietary fuel may matter.

To round out those findings, the Nature Metabolism study looked at where the metabolites we find in the body actually come from. It’s easy to assume that if a metabolite is associated with the gut microbiome, the bacteria must have made it. But researchers found that may not always be the case. Using isotope tracing, they found that our own cells can produce many of the metabolites that have been historically attributed to gut bacteria. Some metabolites did depend heavily on the microbiome, while others could be produced by the body’s cells, which suggests that both an individual and its microbes can contribute to the various metabolites circulating in the body.

The results from both studies offer an interesting perspective of the relationship between diet, the gut microbiome and our metabolism. What we eat can influence our gut health and, in turn, what it produces.

How Does This Apply to Real Life?

Similar to a lot of nutrition research, these two studies reveal that multiple parts of your diet can influence your gut microbiome, for better or for worse. Fiber and certain plant proteins—specifically proteins imitating fiber—resist digestion and provide a beneficial source of fuel for your gut microbes. On the other hand, without adequate dietary fuel, gut bacteria may turn to proteins produced by your body, including proteins found in the mucus that protect your intestinal lining.

The findings from these studies add to a growing body of research suggesting that the gut microbes benefit from a diverse diet that provides them with plenty of different nutrients (especially plant-based nutrients) to work with. If you’re looking to add more plant-based choices into your diet, here are a few simple strategies:

• Add a source of fiber with each meal and snack. Fiber-rich foods like vegetables, fruits, whole grains, lentils, nuts and seeds are good options.
• Replace some animal-based protein with plant-based protein. Instead of overhauling and following a completely vegetarian or vegan diet, try replacing some animal protein with plant protein. Beans, lentils, tofu, tempeh and edamame are good starting points.
• Don’t just focus on one type of plant food. Eating a variety of fruits, vegetables, whole grains, legumes, nuts and seeds gives your gut microbes access to more beneficial nutrients.
• Increase fiber gradually. A sudden increase can cause digestive discomfort, so give your gut some time to adjust.
• Don’t replace fiber with protein. While proteins imitating fiber are an interesting new area of research, they aren’t a replacement for dietary fiber. Fiber remains an important part of a balanced diet and a well-studied source of fuel for gut microbes.

Our Expert Take

These recent findings suggest that proteins imitating fiber may work alongside dietary fiber to nourish your gut microbiome and influence the metabolites your microbes produce. While there is already a large body of research supporting plant-based eating patterns, these studies offer new insight into why these foods may benefit the gut. They also serve as a helpful reminder that nourishing your gut microbiome with a variety of plant foods can provide microbes with plenty of dietary fuel to work with, potentially reducing their need to turn to proteins produced by the body as an alternative food source.