The Effect of Probiotic Foods on Depression

Nadide Gizem Tarakci Filiz30 enrolled

Overview

This exploratory study examined whether different frequencies of consuming three fermented foods commonly eaten in Türkiye-kefir, tarhana, and mixed pickles-were associated with short-term changes in body measurements and psychological well-being in adults. Thirty adults aged 18 to 55 years were randomly assigned to one of three groups for four weeks. The control group followed an individualized dietary plan that excluded fermented foods. The lower-frequency group followed a similar dietary plan and consumed kefir, tarhana, and mixed pickles once per week. The higher-frequency group consumed kefir daily, tarhana four times per week, and mixed pickles three times per week. Body weight, body mass index, waist circumference, mid-upper arm circumference, estimated body fat measures, depressive symptoms, and general psychological distress were assessed at the beginning and end of the four-week intervention. The study was designed as an exploratory dietary intervention and did not have a prespecified primary outcome.

This was an exploratory, three-arm, parallel-group randomized dietary intervention conducted in adults living in Istanbul, Türkiye. The study evaluated two different frequencies of incorporating kefir, tarhana, and mixed pickles into individualized dietary plans over a four-week period. Thirty participants were randomly allocated in a 1:1:1 ratio to a control group, a lower-frequency fermented-food group, or a higher-frequency fermented-food group. All participants received individualized dietary plans based on estimated daily energy and nutrient requirements. The control-group plan excluded fermented foods. In the intervention groups, the study foods were added to the individualized dietary plans rather than replacing other prescribed food servings. Participants in the lower-frequency group were instructed to consume one serving each of kefir, tarhana, and mixed pickles once per week. Participants in the higher-frequency group were instructed to consume kefir daily, tarhana soup four times per week, and mixed pickles three times per week. One serving was defined as 200 mL of kefir, one serving of tarhana soup prepared with 20 g of powdered tarhana, and 100 g of mixed pickles. The intervention schedules were intended to create a pragmatic contrast between occasional and more frequent fermented-food consumption rather than microbiologically standardized doses. Anthropometric assessments included body weight, body mass index, waist circumference, mid-upper arm circumference, estimated body fat percentage, and estimated body fat mass. Psychological outcomes included depressive symptom severity assessed using the Beck Depression Inventory and general psychological distress assessed using the General Health Questionnaire-28. Assessments were performed at baseline and after the four-week intervention. The study was exploratory and did not have a prespecified primary outcome. All anthropometric and psychological outcomes were analyzed as exploratory study outcomes.

Interventions

Individualized diet excluding fermented foodsOTHER

Participants followed an individualized dietary plan based on estimated daily energy and nutrient requirements for four weeks. Fermented foods were excluded from the dietary plan, and participants were instructed not to consume additional fermented foods or probiotic supplements during the intervention.

Lower-frequency fermented-food dietary interventionOTHER

Participants followed an individualized dietary plan for four weeks with the addition of kefir, tarhana soup, and mixed pickles. Participants consumed one 200-mL serving of kefir once per week, one serving of tarhana soup once per week, and one 100-g serving of mixed pickles once per week. One serving of tarhana soup was prepared with 20 g of powdered tarhana, 200 mL of water, 5 g of olive oil, and 5 g of tomato paste.

Higher-frequency fermented-food dietary interventionOTHER

Participants followed an individualized dietary plan for four weeks with the addition of kefir, tarhana soup, and mixed pickles. Participants consumed one 200-mL serving of kefir daily, one serving of tarhana soup four times per week, and one 100-g serving of mixed pickles three times per week. One serving of tarhana soup was prepared with 20 g of powdered tarhana, 200 mL of water, 5 g of olive oil, and 5 g of tomato paste.

Outcomes

Primary Outcomes

Depressive symptom severity assessed by the Beck Depression Inventory (BDI)

Depressive symptom severity was assessed using the 21-item Beck Depression Inventory (BDI). Each item is scored from 0 to 3, yielding a total score from 0 to 63. Higher total scores indicate greater depressive symptom severity. The BDI was administered at baseline and after the four-week dietary intervention. The original ethics application focused on depression and general health but did not formally classify outcomes as primary or secondary. For retrospective registration, depressive symptom severity assessed by the BDI is listed as the primary outcome because depression was the principal focus reflected in the original study title.