Consuming adequate amounts of fiber has a ton of well-known health benefits, from promoting healthy digestion to increasing satiety to regulating blood pressure. But one of the most interesting—and, perhaps, least-discussed—is its relationship to mental health. “Fiber helps feed the microorganisms in our body, regulating the microbiota, the immune system, and blood glucose,” explains nutrition coach Cristina Barrous. “This in turn has a positive impact on serotonin, dopamine, and cortisol, which play a crucial role in regulating mood and reducing stress,” she says.
Indeed, studies show that eating fiber is linked to a number of positive mental health outcomes— especially in terms of regulating mood, reducing stress, and easing symptoms of depression and anxiety. If that sounds like good news—and a good excuse to up your intake of flaxseed, fruits, and veggies—read on.
The gut-brain axis
Fiber is an essential ingredient for gut health. Fiber contains prebiotics, which feed the beneficial bacteria in the gut, a.k.a. the gut microbiome. These bacteria not only regulate cortisol, they help the gut to produce feel-good neurotransmitters (chemical messengers) such as serotonin and dopamine, which in turn influence mood.
You can think of this interaction between the brain and gut as a two-way path that signals in both directions: “The gut-brain axis (GBA) consists of bidirectional communication between the central and the enteric nervous system, linking emotional and cognitive centers of the brain with peripheral intestinal functions,” notes a study that examined this function. “It interacts with the central nervous system (CNS) by regulating brain chemistry and influencing neuro-endocrine systems associated with stress response, anxiety, and memory function.” In other words, when the gut microbiota is working optimally, dopamine and serotonin are more available to stabalize our moods.
Because of this, higher fiber intake is actually related to lower levels of depression and anxiety symptoms. “Total dietary fiber intake might have a role in preventing anxiety, depression, and distress,” notes a 2021 study that examined how fiber impacts psychological disorders in adults. “More consumption of dietary fiber was also related to reduced odds of depression in women,” the study explains.
Reduced inflammation
Another key way fiber helps the gut? It reduces inflammation, another factor associated with mental health conditions like depression and anxiety. “Increased inflammatory biomarkers including inflammatory cytokines have indeed been found in patients with major depression and generalized anxiety disorder,” notes a 2024 study that looked at the way fiber intake influences maternal mental health issues. “Many features of a ‘healthy’ diet attributed to positive mental health outcomes may include the higher content of antioxidants, phytochemicals, vitamins, and minerals. Additionally, the greater consumption of whole fruits, grains, and greens, naturally exposes individuals to a greater amount of dietary fiber, which is a key modifier of the microbial profile.”
Blood sugar and sleep
Sleep not be the first thing you think about when it comes to fiber’s benefits, but getting enough fiber might help you sleep better, too—and we all know how a good night’s sleep can work wonders on your mood.
Here’s how it works: Because fiber can’t be digested by the body and contains no sugar or calories, it helps prevent blood sugar spikes and crashes. A stable blood sugar level mean you’re less likely to wake up in the middle of the night and more likely to experience the full cycle of sleep. As researchers at the University of Colorado Boulder have pointed out in numerous recent studies, eating a prebiotic-rich diet (i.e., fiber-rich) seems to allow for more time in restorative non-rapid-eye-movement (NREM) sleep as well as in rapid-eye-movement (REM) sleep, “which is believed to be critical for recovery from stress.”
More fiber, more happiness?
Does this mean you should eat more fiber in order to feel happier? Considering that many of us don’t eat enough fiber and that mental health concerns are also on the rise, it couldn’t hurt. “Most people consume between 30-40% less fiber than they should,” says Barrous.
That said, it’s best to start slowly when introducing more fiber to your diet—especially if a diet filled with legumes, whole grains, and raw veggies is new to you. As we’ve all likely experienced at some point, a sudden influx of fiber can cause bloating and other discomforts, so be sure to introduce fiber-rich foods to your diet a little at a time in order to give your intestines time to adjust. “The microorganisms of your microbiota would prefer you don’t suddenly go from 0 to 100,” says Barrous.
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