Of course we all know, we should eat fiber. But, did you know there is a “right” type of fiber?! Scientists have just shown that some sources of fiber are actually more beneficial for your gut health than others.

By Lena Baumann and GUTXY Editor Dietary fiber is actually more complex than we think. Whether we eat it in an apple, or apple-crisp cereal, makes a difference. As we know, fiber is found in many different foods. Yet, it also comes in different types. Since they all have their own complex structures, and biological effects, it's no surprise that they likely impact our bodies differently. Unfortunately, experts have been missing detailed knowledge on these differences, and their biological significance. We'd all like to know: is fiber from different sources equally beneficial? Luckily, scientists decided to test just that.

Different fiber, different effects

Researchers at the Washington University School of Medicine in St. Louis conducted a study to test how different sources of fiber affect the abundance of gut bacteria. In this mice study, the animals were bred under sterile conditions, so they did not have their own gut microbiomes. Instead, they each got a 20-strain cocktail of Bacteroides, a common type of gut bacteria, that had been isolated from a human gut. Afterwards, each mouse was given a selected diet for 4 weeks, essentially a base diet with supplementary fiber. The base diet was a model of a typical Western diet, and was made up of a high amount of saturated fats, and low in fruits and vegetables – and, therefore, fiber. Different types of fiber were then added to this base. In total, 34 different sources were tested, including pea protein, citrus peel, citrus pectin, tomato peel, orange fiber, apple fiber, oat hull fiber, cocoa, chia seeds, and rice bran. This meant a final total of 144 combinations!

Notably, the abundance of B. thetaiotaomicron increased in the presence of citrus pectin and pea fiber, whilst B. ovatus levels rose in conjunction with barley beta-glucan and barley bran.

With that, the team then analysed how the various 20 bacterial strains actually reacted to the presence of the various fiber sources. They found significant effects in 21 of the combinations, whose strains’ they deemed to have “distinct nutrient harvesting capabilities.” Notably, the abundance of B. thetaiotaomicron increased in the presence of citrus pectin and pea fiber, whilst B. ovatus levels rose in conjunction with barley beta-glucan and barley bran. Other fibers that inspired increases in Bacteroides strains were high molecular weight inulin, resistant maltodextrin, and psyllium.

Fiber ≠ fiber: Choose the right type

Fiber is not fiber. Is it not only important that we eat fiber, but moreover that we eat the right type of fiber! As this research shows, some might have more beneficial effects than other: certain components of dietary fiber actually encourage the growth and metabolic activity of gut microbes linked with good health.

Certain components of dietary fiber actually encourage the growth and metabolic activity of gut microbes linked with good health.

For instance, it may be worth choosing fiber in citrus fruits, peas or barley, particularly over processed and fortified foods that proudly proclaim their fiber richness. According to WHO recommendations, you should eat 25 – 29 gram fiber each day to lower your risk of Type 2 diabetes, heart disease, stroke and colon cancer. Fortunately, it’s not that hard to do! Simply sprinkle some nuts and seeds over your morning oats, add peas or beans to your salad/soup at  lunchtime, snack on citrus fruits and replace white rice with barley or bulgur for dinner. As knowledge in this area develops, researchers hope to decipher which dietary ingredients beneficial microbes crave. This can help us craft our meals in a way that means well for our microbiome.
Reference:
  1. Patnode ML, et al. Interspecies competition impacts targeted manipulation of human gut bacteria by fiber-derived glycans. Cell. Sept. 19, 2019. DOI: 10.1016/j.cell.2019.08.011.