This randomized controlled study examined supplementation with inulin and oligofructose dietary fibres and its effects on digestive function and intestinal microflora. It reported increased intestinal Bifidobacterium levels and improved measures of depression, anxiety and mood in adults with mild to moderate anxiety and stress
.


What was studied
?


The effects on the gut microbiome and mood of two inulin-type fructans
 (ITFs), 
oligofructose (also called fructooligosaccharide) and 2′-fucosyllactose
.


The primary outcome was an increased microbiome count of
 Bifidobacterium. 
Secondary outcomes included improvements in depression, anxiety symptoms, mood, sleep quality, salivary cortisol measures, urinary metabolites, gastrointestinal sensations and bowel habits.


Study design:

The researchers conducted a randomized controlled trial
 (RCT) 
lasting 5 weeks with 4 groups. Participants were randomly assigned to receive the following
:

Maltodextrin (placebo), oligofructose, inulin, or a combination of the two fibres, 8–10 grams per day.

  • Stool samples were collected and analysed for intestinal bacterial load and composition.
  • Mental health was assessed using several questionnaires
    : Beck Depression Inventory (BDI); 
    for depression
    ), STAI (
    for anxiety), versions
     Y1 
    and
    -Y2, 
    and the Positive and Negative Affect Schedule
     (PANAS-SF, 
    for aspects of mood).
  • Sleep quality was assessed with the Pittsburgh Sleep Quality Index
     (PSQI) .
  • Urine and saliva were collected to assess changes in urinary metabolites and the cortisol awakening response.
  • Bowel habits and gastrointestinal sensations were monitored with a daily diary and the Bristol Stool Scale during the final intervention week and the week before the intervention
    .

 


The broader picture:

Higher dietary fibre intake is associated with a lower risk of some mental health disorders, such as depression. Dietary fibres are carbohydrates that humans cannot digest or absorb but that intestinal microbiota can ferment to varying degrees. A fibre may be classified as a prebiotic if it causes specific changes in the composition and/or activity of intestinal bacteria that improve host health. Mental health disorders have been associated with an imbalanced gut bacterial profile (dysbiosis), with fewer friendly bacteria and more pathogenic bacteria. Prebiotics and probiotics have therefore been proposed as potentially useful for mental health through the gut–brain axis. Indeed, irritable bowel syndrome
 (IBS) 
is consistently associated with mental health disorders. Substances affecting gut–brain signalling, including prebiotics, probiotics, synbiotics and fermented foods, have been proposed as key components of interventions to improve depression management alongside other dietary, medical and psychological interventions
.


Inulin-type fructans (
ITFs
) are among the few dietary fibres accepted by the International Scientific Association for Probiotics and Prebiotics (
ISAPP
) as prebiotics because of their bifidogenic action (ability to stimulate bifidobacteria) and beneficial health effects
.


Conclusions:

Increasing inulin and oligofructose dietary fibre intake was shown to directly affect
Bifidobacterium 
and was associated with a greater bifidogenic effect of the intervention.

Higher dietary fibre intake (39 grams per day) was associated with a greater and more favourable intestinal microbial response, particularly an increase in
Bifidobacterium
, in response to the
ITF
intervention (a 50:50 inulin–fructooligosaccharide blend), compared with the usual low-fibre diet (18 grams per day).


A direct gut–brain axis relationship between fibre intake and mental health was reported. The overall trend suggests that greater fibre intake, preferably from whole foods, improves mental health, but should be combined with other psychological and medical interventions for optimal treatment.

References

^Liangkui Li, Peng Li, Li XuAssessing the effects of inulin-type fructan intake on body weight, blood glucose, and lipid profile: A systematic review and meta-analysis of randomized controlled trialsFood Sci Nutr.(2021 Jun 21)

^Saghafian F, Hajishafiee M, Rouhani P, Saneei PDietary fiber intake, depression, and anxiety: a systematic review and meta-analysis of epidemiologic studies.Nutr Neurosci.(2023-Feb)

^Liu Y, Ju Y, Cui L, Liu T, Hou Y, Wu Q, Ojo O, Du X, Wang XAssociation between Dietary Fiber Intake and Incidence of Depression and Anxiety in Patients with Essential Hypertension.Nutrients.(2021-Nov-20)

^Saghafian F, Sharif N, Saneei P, Keshteli AH, Hosseinzadeh-Attar MJ, Afshar H, Esmaillzadeh A, Adibi PConsumption of Dietary Fiber in Relation to Psychological Disorders in Adults.Front Psychiatry.(2021)

^Holscher HDDietary fiber and prebiotics and the gastrointestinal microbiotaGut Microbes.(2017 Mar 4)

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