The study, published in Nutrition, tested the associations between dietary intakes of total, soluble, insoluble, and sources of fibre with depressive symptoms in data from nearly 2,000 Japanese workers – finding that vegetable and fruit fibre intake were inversely associated with depression.
Led by Takako Miki from the National Center for Global Health and Medicine and the The University of Tokyo, the research team noted that previous research has suggested that dietary intakes of fibre could play a role in mood and behaviour through its impact on the gut microbiota.
“But epidemiologic evidence linking mood to dietary fiber intake is scarce in free-living populations,” they reported, noting that previous studies that have identified an association have either not provided statistically significant results or have failed to adjust for potentially important cofounders like the intake of other nutrients, sleeping habits and physical activity.
“In this cross-sectional study, we found that higher intake of dietary fiber derived from vegetables and fruits was associated with a lower prevalence of depressive symptoms in Japanese workers, even after adjusting for a wide variety of potentially important dietary (…) and non-dietary confounders,” said Miki et al. “In contrast, dietary intake of total, soluble, insoluble, and cereal fiber was not associated with depressive symptoms.”
Miki and colleagues examined the association between dietary fiber intake and depressive symptoms using data from 1977 Japanese employees aged between 19 and 69 who took part in the Furukawa Nutrition and Health Study.
Dietary intake was assessed through a diet history questionnaire, while depressive symptoms were assessed using the Center for Epidemiologic Studies Depression Scale.
The team then used logistic regression analysis to evaluate the associations between fibre intake and of depressive symptoms after adjustment for a range of dietary and non-dietary potential confounders including: folate, vitamin B6, vitamin B12, omega-3 polyunsaturated fatty acids, magnesium, zinc, coffee, and green tea.
After adjustment for co-founders, the Japanese team found that dietary fiber intake from vegetables and fruits was significantly inversely associated with depressive symptoms, while intake of total, soluble, insoluble, and cereal fiber was not associated with depression.
The Japanese researchers added that while a firm mechanism linking depression to dietary fibre is ‘unclear’, several possibilities have been suggested by previous research projects.
Indeed, an emerging body of evidence suggests that the gut microbiota is potentially important to depression, given its ability to influence neurotransmitters like serotonin, inflammation, oxidative stress, and the stress response, said Miki and colleagues.
“Fibre can alter the composition of the intestinal flora, and bacteria in the gastrointestinal tract can communicate with the central nervous system,” they noted. “In addition, SCFAs, neuroactive bacterial metabolites of dietary fibres, can modulate brain and behavior.”
Based on these mooted mechanisms, the team suggested that the stronger association between depression status and vegetable and fruit fibre intake “could be ascribed to its more readily fermentable properties.”
“In addition, inulin and oligofructose, which are mainly presented in vegetables and fruits and, have been shown to increase bifidobacteria,” they added.
Volume 32, Issue 5, May 2016, Pages 584–589, doi: 10.1016/j.nut.2015.11.014
“Dietary fiber intake and depressive symptoms in Japanese employees: The Furukawa Nutrition and Health Study”
Authors: Takako Miki, et al