Gut Health: The Impact of Fiber and Indigestible Proteins

Plant-based diets have been touted as a key component of a healthy lifestyle, and for good reason. Not only do they support weight management, but they also have a profound impact on our gut health. Research has shown that the diverse population of bacteria in our intestines plays a crucial role in our overall well-being, and dietary fiber is a key contributor to this process.

Scientists have long known that dietary fiber contributes to the benefits associated with plant-based diets. However, researchers are still working to understand exactly how gut bacteria process the many components of plant foods and how those interactions produce beneficial effects. Two recent studies led by Jenna AbuSalim and Joshua Rabinowitz of the Ludwig Institute for Cancer Research offer new insight into this process.

Study 1: The Impact of Fiber and Indigestible Proteins on Gut Health

In their study published in the Proceedings of the National Academy of Sciences, AbuSalim and Rabinowitz examined how plant-based foods influence phenol metabolites. Gut bacteria create these compounds when they digest the amino acids tyrosine and phenylalanine, but the resulting metabolites can have very different effects on health.

The researchers found that both the fiber and indigestible proteins from plants, which they refer to as ‘proteins imitating fiber’ (Prif), shift the balance of phenol metabolites from the harmful kind made from tyrosine to the healthful variety derived from phenylalanine. Fiber has long been recognized as an important part of a healthy diet, but indigestible plant proteins have received far less attention.

The researchers also discovered that Prif are processed by gut microbes and can alter both the makeup of the microbiome and the host’s metabolism. Working together with indigestible plant fiber, they can also change the metabolic activity of gut bacteria in ways that favor the production of beneficial phenols.

Study 2: The Origins of Phenol and Indole Metabolites

The second study, published in Nature Metabolism, focused on the origins of phenol and indole metabolites. Researchers had generally assumed that these compounds were produced only by gut bacteria. However, AbuSalim, Rabinowitz, and their colleagues decided to test this assumption using isotope tracing in mice, rats, and human cells.

The researchers found that mammalian metabolism can produce many indole and phenol metabolites on its own. These included important compounds such as indole-3-lactate and indole-3-acetate. In mice, circulating levels of these metabolites remained high even after antibiotic treatment disrupted the microbiome.

A similar pattern appeared in samples from patients taking antibiotics, including cancer patients. At the same time, metabolites made exclusively by microbes, including indole-3-propionate and p-cresol sulfate, declined after antibiotic treatment.

The findings of these two studies provide a clearer picture of where phenol and indole metabolites come from and how they are produced. The researchers believe that understanding these interactions will help them develop therapies designed to raise or lower specific metabolites.

The studies were funded by the Ludwig Institute for Cancer Research, the National Institutes of Health, the National Institute of Diabetes and Digestive and Kidney Diseases, the Princeton Alliance for Collaborative Research and Innovation, and Princeton University.