Fiber is good for health—that much we know. But for decades, scientists have been searching for the answer to a very simple question: how does dietary fiber manage to benefit the body?

The answer turns out to be quite complicated. Currently, scientists think the gut microbiota plays a pivotal role in the how fibre benefits health—and it’s mostly thanks to their host of molecular messengers, called short-chain fatty acids (SCFAs).

SCFAs are molecules produced by bacteria when they ferment dietary components (primarily fibre: non-digestible carbohydrates) inside the colon. Some of these molecules stay close to home in the gut, but others travel far and wide throughout the body, taking part in complex interactions that produce various effects on health and are the subject of active scientific study.

SCFAs (in particular, butyrate) have anti-inflammatory effects and may play a role in protecting the body against colorectal cancer.

First, SCFAs have effects in the gastrointestinal (GI) tract that influence gut health. In fact, their main reason for existence is serving as a source of energy for cells inside the colon. They help boost the protective mucus layer in the gut and also have the ability to influence genes that control cell proliferation and cell cycle (whereby cells prepare to divide and duplicate their DNA). Not only that, SCFAs are under investigation for their apparent influence over gut motility—the muscular contraction responsible for propelling the intestinal content through the GI tract during digestion process—in both humans and animal models.

SCFAs also have an effect on how energy is metabolized in the body, and thus, a possible protective effect against metabolic disease and obesity. Evidence on this, however, is somewhat contradictory. Studies show SCFAs seem to reduce levels of cholesterol and glucose—which would ultimately protect against obesity—but at the same time, they provide a source of calories in the gut that could contribute to obesity. More study is needed on this link.

Another known influence of SCFAs is on the immune system. Research shows that SCFAS (in particular, the SCFA butyrate) have anti-inflammatory effects and seem to play a part in kick-starting the differentiation (that is, specialization) of immune cells that help ‘keep the peace’, called regulatory T cells. And if that weren’t enough, SCFAs may play a role in protection against colorectal cancer, by favorably altering the gut environment or perhaps by modulating the immune system in a way that reduces cancer risk.

At this stage, there’s no doubt that SCFAs are important molecules—one of the main ways in which the gut microbiota and diet co-contribute to better health. Since the production of SCFAs by bacteria in the body is influenced by food intake, many scientists believe they are a key link between diet, the gut microbiome, and health.

Get the quick overview of SCFAs in our infographic here.

If you want to go deeper into the science on this topic, feel free to check out our new “best of” document on gut microbiota & short-chain fatty acids.