Scientists continuing to study how fibre aids gut microbiome

DEAR DOCTOR: I know that all sorts of studies show that fibre is good for you, but has anyone figured out the reason why?

DEAR READER: You’re right — the upside of fibre has been with us for quite a while now. Not only has the list of proven health benefits continued to grow, but also the language itself has changed: It used to be referred to as “roughage”. But whatever it’s being called, fibre is basically the carbohydrates in our food that resist digestion. And though there has been plenty of educated guessing about why we do measurably better over the short and long haul with a regular supply of fibre in our diets, a definitive answer has proven elusive. Now, however, ongoing research into the gut microbiome is offering up some intriguing answers.

First, some of what researchers had already believed about fibre’s benefits continue to hold true. Foods that are high in fibre help to slow the absorption of sugars during digestion, which is a boon in regulating blood sugar levels. As a result, fibre in the diet can be a hedge against developing diabetes.

Fibre makes you feel full after a meal, helps lower inflammation, and its presence in the intestines aids in elimination. Research shows that a diet high in fibre results in lower rates of heart disease and certain cancers, which may be why eating lots of fibre has been linked to a longer lifespan in general.

What’s really interesting is scientists are now discovering that the fibre we consume feeds the billions of micro-organisms each of us hosts in our bodies. Better known as the gut microbiome, it’s becoming clear that they play an important role in keeping us healthy. If that number sounds like a lot, you’re right. It’s now estimated that these tiny hitchhikers make up between 1- 3% of a person’s total body weight. That means if your scale says 60kg, up to 1.8kg of that weight is beneficial bacteria. And since both quantity and diversity of beneficial bacteria are equally important, making sure they stay fed and happy is key.

Recent studies suggest that the way to cultivate a strong gut microbiome is keeping it supplied with plenty of fibre. When mice were put on a diet loaded with fat and low on fibre, the number and diversity of bacteria in their guts plummeted. At the same time, the mice themselves underwent changes that adversely affected their health. Not only did their intestines shrink, the protective coating of mucus along the intestinal walls became dangerously thin. This woke up the immune system and triggered an inflammation reaction. In time, this chronic inflammation was associated with weight gain and unhealthy blood sugar levels.

Bottom line — the fibre you consume feeds the beneficial gut bacteria that help to keep us healthy in ways we don’t yet fully understand and have yet to discover. So, when you’re having that salad of leafy greens, a handful of walnuts, an apple or banana, or a serving of beans, you’re not just eating for one — you’re eating for a few billion. Dr Eve Glazier is an internist and assistant professor of medicine at UCLA Health. Dr Elizabeth Ko is an internist and primary care physician at UCLA Health.