Fiber, you have probably noticed the screaming advertisements in the supermarket on specific bars, cereals, and other products. However, why do manufacturers put so much emphasis on this specific food component? Your answer would probably be something like: ‘It is good for our health’, which is technically speaking correct, but what is its effect on brain health specifically? In this article, we will dive into the latest research around fiber and its beneficial effects on cognition.
Let's get on the same page, and explain what we mean by dietary fiber. The definition has undergone some changes, but is nowadays defined as a carbohydrate that cannot be cut into small pieces by protein units called enzymes. Therefore, dietary fibers do not release energy like other carbohydrates do. Nevertheless, dietary fibers are a crucial part of our diet, especially if we are talking about our brain.
In our previous articles, we introduced you to the microbiota-gut-brain axis. This axis forms a highway between our gut and brain and is important for transferring signals and other metabolites between them. The fermentation of dietary fiber by bacterial species in our gut results in the build-up of gut hormones, which among others regulate our hunger cues, and microbial metabolites such as short-chain-fatty-acids or SCFAs. These SCFAs like butyrate, acetate, or propionate are important among others for the communication between the microbiota and the brain and enhance neurotransmitter production. Another proposed pathway how dietary fiber exerts influence on cognition could be via the immune system. However, up to this date these possible pathways have only been studied mechanistically in animals.
Crucially, our Westernized diet stands in sharp contrast to the current fiber guidelines that tell us to eat 25 to 30 grams of dietary fiber per day. In the Netherlands, the average intake lies somewhere between 15 to 23 grams, so there is plenty of room for improvement! Luckily, as my colleague who is a dietician told me during my internship, it is relatively easy to make small adjustments in your diet to hit this fiber target. Before I will provide you with two of his tips and tricks that blew my mind, I will give a summary of what research currently has shown regarding fiber and its effects on cognitive performance.
Mao and colleagues published in 2019 the results of their study in which the fiber intake of 3316 participants was followed for 25 years. After these years they measured their cognitive performance. Interestingly, higher fiber intake throughout young adulthood was associated with better memory of learned words during midlife. Moreover, Khan and colleagues already showed in 2015 that fiber intake was associated with better adaptation skills in prepubertal children, also known as cognitive control. As for both studies it is crucial to mention that correction was applied for certain variables such as exercise, socioeconomic status, education level etc.. Otherwise, we could have argued for example that a high intake of fiber is mostly seen in higher income households that are either better educated, or can afford to spend extra money on a healthier lifestyle. If it’s the latter, then it is also likely that these same families can afford better education for their children, leading to improved cognitive performance later in life. However, what is still missing from these observational studies such as the ones described above, is that it is only possible to speak about a positive correlation between for example higher fiber intake and cognitive performance. Therefore, it remains unclear whether it is fiber alone that accounts for these improvements or if other nutrients also play a role here.
In contrast, interventional studies looking at the effects of supplementation of one dietary fiber specifically or diets high in fiber can give us more information. Berding and colleagues showed in 2021 that supplementation of daily meals with a specific dietary fiber named polydextrose in healthy females resulted in improved cognitive flexibility and sustained attention, which was not seen in the females receiving only a placebo. Another study performed by Chung and colleagues in 2012 put 28 high-school students on either a mixed-grain diet or a regular diet for 9 weeks. Interestingly, the mixed-grain diet high in fiber was shown to be protective. The regular diet group scores on a mental fatigue task indicative of cognitive control were lower after 9 weeks compared to their scores at the start. This was in contrast to the mixed-grain group whose scores stayed consistent over time.
This sounds quite promising, right? Well, the current evidence is too scarce to boldly state that dietary fiber enhances cognitive performance, but the results described above certainly point into that direction. What is missing from current research is a controlled study with many participants as well as data about what happens in the gut when people switch their fiber intake. If these two types of studies will be conducted in the future, we can be more certain about which type of fiber digested in our gut results in beneficial products that travel to our brain to influence our cognition. Nonetheless, I can confidently say that the last word about fiber and its effect on cognition has yet to be spoken, since studies are on their way to further unravel its relationship!
So in the meantime, there is no harm in eating popcorn as a snack from time to time or adding some cocoa powder to your porridge in the morning. You might be surprised about how much fiber you add to your diet with these small and easy adjustments which will probably and hopefully taste delicious to you as well.
Author: Joyce Burger
Illustration: AI (Bing image creator)