We're learning more about why one type of carb is so good for you

  • Fibre is a key ingredient found in whole grains and produce that appears to help with weight loss and overall health.
  • We’ve known for decades that fibre helps with digestion and keeps us feeling full, but scientists haven’t known why that is.
  • Two new studies suggest that fibre’s most important impact is on the bacteria that thrive in our gut – a finding that jives with some research published in the 1990s.

Not all carbs are created equal.

Whole grains like those found in wheat bread, as opposed to their refined cousins like white bread, are a key component of a healthy diet. A growing body of research suggests that several components of whole grains make them healthy cornerstones of any diet, but one of the most mysterious of those ingredients is fibre.

Scientists and nutritionists know that fibre – which can be found in whole grains as well as fruits and vegetables – assists with digestion and keeps us feeling full. Diets rich in fibre have also been linked with a reduced risk of diseases like diabetes and arthritis, and even a lower risk of death from all causes. Nutritionists and dietitians have been suggesting we eat more of it for decades.

Yet what experts aren’t as clear on is why the ingredient appears to be so beneficial. The results of two studies on mice, published this winter, shed some light on this enduring mystery – especially since their findings jibe with the conclusions of a handful of small studies in humans published between the 1980s and early 2000s.

They essentially conclude that fibre helps nourish the diversity of bacteria that thrives in our guts, also known as our microbiome. By keeping these bacterial communities healthy and varied, high-fibre diets appear to be help with weight loss, staving of disease, and keeping us healthier overall. It’s why fibrous foods are sometimes called “prebiotics” – “pre” as in before or generating, and “biotics” as in life.

The latest research suggests fibre’s biggest benefit is on our guts

For a study of fibre’s impacts on mice, published in December 2017 in the journal Cell Host, researchers from Georgia State University fed the rodents a high-fat, low-fibre diet then tested the amount of bacteria in their guts.

Within a few days, the diverse bacterial communities flourishing in the animal’s gut microbiome flat-lined.

In a similar experiment published in the same journal, researchers at the University of Gothenburg in Sweden put mice on a low-fibre, high-fat, high-sugar diet and observed the changes that occurred within their guts.

Essentially, the low-fibre diet appeared to flip the delicate balance of bacterial populations in the mice’s guts – some of the sparsest species of bacteria suddenly blossomed, while the most common species shriveled.

Scientists have been performing studies like these in humans since the 1990s, but most of them have involved small numbers of people. A handful of research highlighted in a 2007 review published in the Journal of Applied Microbiology suggested that the reason fibre and other prebiotics were so beneficial was that they appeared to promote the growth of beneficial bacteria in the gut.

While some of these studies focused on the compounds produced by fermented foods like sauerkraut, others looked exclusively at inulin, otherwise known as dietary fibre. Together, these prebiotics “beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon and thus improve health,” according to a 1995 paper published in the Journal of Nutrition.

“Prebiotics are arguably a practical and efficient way to manipulate the gut microflora,” the authors of the 2007 review wrote.

Whole grains vs. ‘stripped carbs’

As opposed to their refined cousins, whole grains are an excellent source of fibre (which is key for healthy digestion), protein (which helps fill you up and power your muscles), and several key vitamins and minerals.

In fact, whole grains are one of the cornerstones of a plant-based diet, which has been increasingly championed by nutritionists and dietitians as the best for your brain and body.

The key difference between whole grains and processed carbohydrates – like white rice and the wheat in white bread – is that the latter has had its nutritious, fibre-rich outer shells, such as the germ and bran, stripped away. The end result is soft bread, smooth rice, and sweet cereal that gets processed by the body almost as quickly as it was ingested.

Business Insider / Anaele Pelisson

While refined carbs may taste delicious, experts agree that they don’t belong in a healthy diet. Unlike their whole-grain counterparts that get digested slowly and fill you up for hours, refined carbs are rapidly turned into sugar in your body.

This is why those ingredients can contribute to weight gain, according to Roxanne B. Sukol, the medical director of the Cleveland Clinic’s Wellness Enterprise. In the book “Grocery: The Buying and Selling of Food in America,” Sukol told author and chef Michael Ruhlman that people should think of things like white rice and white bread as “stripped carbs.”

Instead of eating those ingredients, Sukol advises people to fill up on more whole grains, which she calls “good carbs.”

So add more brown rice, fruits, and vegetables to your diet. Your gut – and entire body – will thank you.

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