Over the past several years, the role that the digestive process and gut microbiome play in mood and mental health outcomes has become a well-established target by those specializing in fiber and probiotics alike. A recent clinical trial involving 2,960 adults who participated in the Korean National Health and Nutrition Examination Survey (KNHANES) found that certain types of dietary fibers appeared to have a significant impact on the likelihood that an individual may have in receiving a depression diagnosis. While previous research postulated that dietary fiber could have an effect on the rates of depression in population-based studies, the authors said they couldn’t find prior studies breaking down the benefits of fiber by source.
 
The participants of this trial, who were between the ages of 19 and 64, provided information about their diet in the form of a food frequency questionnaire, which researchers used to determine the quantities of various types of fiber each participant was consuming – the fiber types were broken down into crude, cereal, vegetable, fruit, seaweed, and mushroom fibers.
 
Incidences of depression among the population were recorded either through questionnaires, or through a self-reported clinical diagnosis by a physician.
 
It was noted by the authors of the study that high seaweed and mushroom fiber intakes were the most inversely associated with depressive symptoms as assessed by a patient health questionnaire, with odds ratios of 0.38 and 0.18, respectively. Notably, there were significantly reduced rates by which those who consumed high amounts of seaweed fibers were clinically diagnosed by a physician, with an odds ratio of 0.45.
 
“This was the first study to find that higher intakes of seaweed and mushroom fiber were associated with a lower likelihood of depression in a representative cohort of Korean adults, indicating that the specific source of dietary fiber may be an important dietary factor in modulating depression,” the authors of the study said. While cereal, vegetable and fruit fibers did have some inverse association with depression incidences, their effect was not significant after adjusting for the results of participant groups from different quartiles.
 
The authors of the study went on to explain that the benefits seen in this particular study may not be generalizable to other populations, due to genetic variations which alter a person’s physiology at the level of the microbiome. In other words, different types of fiber may yield different benefits depending on the population in question.

“For example, genes for the algal polysaccharide porphyrin in the microbiomes, which determine a carbohydrate qualified as a MAC [microbiota-accessible carbohydrates], were present in Japanese people, but were rarely found in North American and European individuals,” the authors wrote. “In addition, it has been suggested that host genotypes also play a role in defining MACs since the host’s genotype affects mucus structure and the efficiency of digestion and the absorption of carbohydrates in the small intestine.”