Eating more plant foods has long been linked to better health.
People who regularly eat vegetables, fruits, beans, nuts, and whole grains tend to have lower rates of heart disease, type 2 diabetes, obesity, and some cancers.
Scientists believe one important reason is that plant-based foods help feed the trillions of bacteria living in our digestive system.
These tiny microbes, known as the gut microbiome, break down food that our bodies cannot digest on their own.
During this process they produce many natural chemicals, called metabolites, that can affect the immune system, digestion, metabolism, and even brain function. Researchers are now trying to understand exactly which foods produce the most helpful compounds.
A research team led by scientists at Ludwig Princeton and Princeton University has now provided important new clues. Their work, published in two separate scientific journals, examined how plant foods influence the chemicals made in the gut and whether some of these compounds really come only from gut bacteria.
The first study focused on compounds called phenols. Some phenols support healthy digestion and body weight, while others have been linked to kidney disease complications and poorer outcomes in people with cancer.
The researchers wanted to understand why different diets change the balance between these helpful and harmful compounds.
They discovered that plant fibre was only part of the answer. Certain plant proteins that are difficult for people to digest also reached the large intestine, where gut bacteria used them as food. The researchers called these proteins ‘proteins imitating fibre’, or Prif.
Experiments showed that fibre and Prif worked together to encourage gut bacteria to make more beneficial phenols while reducing production of less healthy ones. Fibre also reduced the breakdown of the protective mucus lining of the gut, lowering the production of harmful compounds.
The second study challenged a long-held scientific belief. Many researchers assumed that several important phenol and indole compounds were made only by gut bacteria. Using isotope tracing in animals and human cells, the scientists found that our own bodies can also produce many of these substances.
Even after antibiotics greatly reduced gut bacteria, levels of several important metabolites remained high. This showed that human cells continued making them. However, compounds known to come only from microbes dropped sharply after antibiotic treatment, confirming that some metabolites still depend entirely on the microbiome.
These discoveries improve scientists’ understanding of how diet, gut bacteria, and human metabolism work together. Instead of looking only at fibre, future nutrition advice may also consider indigestible plant proteins as another valuable nutrient for supporting gut health.
The findings may also influence future medical treatments. Researchers hope they can eventually adjust the gut microbiome through diet to reduce harmful metabolites and increase beneficial ones, potentially helping prevent or treat a range of chronic diseases.
This research provides a more complete picture of how plant-based foods influence health. A major strength is that it combined advanced laboratory techniques with animal and human evidence.
However, much of the work remains experimental, and more clinical studies are needed before these discoveries can be translated into dietary recommendations or new therapies.
Even so, the findings highlight that the health benefits of plant-rich diets are more complex than previously thought and extend beyond fibre alone.
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