“When total fiber intake was at approximately 21 grams per day, the risk of depressive symptoms reached a relatively low level, which has important public health implications,” the researchers wrote in their paper, due for publish in the October 2018 edition of the journal Nutrition.
The results were consistent even after adjustment for a wide variety of potential confounders, they added.
The researchers from The School of Public Health of Qingdao University looked at data from the 2007 to 2014 National Health and Nutrition Examination Survey (NHANES) results, a publicly available data set of the dietary habits and nutritional status of more than 16,000 US individuals.
They were building on previous research exploring a link between dietary fiber consumption and depression symptoms, such as a 2016 study published in the same journal, which suggested that higher fiber intake among Japanese employees may result in lower risk of depression.
But the combined scientific literature on the topic reveals mixed results, with many researchers of such studies arguing that outcomes may be specific to different populations.
“Thus, the purpose of the present study was to evaluate the associations among dietary intakes of total, cereal, vegetable, and fruit fiber and depressive symptoms in US adults,” the researchers of this present study wrote.
Public health implications
The authors concluded that, based on NHANES data, US adults who consumed 21 grams of fiber per day were less likely to exhibit depression symptoms as defined by the survey’s parameters.
They evaluated dietary fiber intakes of total cereal, vegetable, and fruit fiber intakes.
However, the usual intake of dietary fiber averaged only 15 grams per day in most Americans, “thus, increasing intake of the foods rich in dietary fiber may be advocated for the prevention of depressive symptoms,” the researchers wrote.
This conclusion mirrors that of several other studies that found a positive link between higher dietary fiber intake and lowered depression symptoms. Possible explanations on the conflicting results with other studies include the different parameters to measure depression symptoms as well as different study population demographics.
Gut-brain axis?
The underlying mechanism of dietary fiber’s impact on depression “remains poorly understood,” the authors added, but they postulated that dietary fiber may modulate the composition of the intestinal microbiota, in turn influencing brain function—a concept dubbed the ‘gut-brain’ axis.
This concept is gaining more popularity not just as a subject for study by researchers, but also as a tool for dietary fiber manufacturers to market their ingredients as ‘prebiotics,’ fibers that can selectively feed beneficial bacteria in the gut to provide health outcomes to the host.
For example, a study presented at the Probiota Americas 2018 conference in Miami last month by Dr. Monika Fleshner of the University of Colorado Boulder revealed that prebiotic supplementation in rats can armor against stress by altering brain structure.
Another proposal is that dietary fiber may lower glucose levels after a meal, inhibiting the inflammatory processes caused by a blood sugar spike.
“Further large-scale prospective studies are needed to confirm our findings,” they added.
Source: Nutrition
Published online ahead of print, https://doi.org/10.1016/j.nut.2018.03.009
“Exploration of the association between dietary fiber intake and depressive symptoms in adults”
Authors: Hui Xu, et al.