## 3 Results
### Effects of Treatment with Psychobiotics
#### 3.1.4 Overall Findings  
Among the studies analyzed, six reported a significant reduction in both physiological and psychological stress-related measures. In a 4-week crossover study involving healthy male participants, _Bif. longum_ 1714 significantly lowered post-SECPT salivary cortisol levels and perceived stress compared to both the placebo and baseline measurements. However, perceived stress levels increased again during the follow-up period [71]. Similarly, _Bif. breve_ CCFM1025 significantly reduced both salivary and plasma cortisol levels in a 4-week RCT with 20 healthy participants [75]. In another study, _L. gasseri_ CP2305 suppressed the escalation of salivary cortisol levels during an examination period in a 12-week RCT. Additionally, this psychobiotic significantly prevented an increase in the STAI-S scores in females prior to examination, although no significant differences were observed in the HADS-A [78]. However, in a separate study, the same probiotic showed no significant effects on salivary cortisol levels after a 24-week double-blind RCT, although it did reduce STAI-T anxiety scores, not STAI-S anxiety scores [79]. A multi-strain probiotic was also found to significantly decrease serum cortisol levels in a 28-day RCT involving 74 participants experiencing academic stress. The probiotic group exhibited a 43.02% reduction in serum cortisol levels, alongside a 38.62% decrease in perceived stress from baseline [84]. Furthermore, supplementation with _L. plantarum_ PS128 TM and _HK-PS23_ significantly reduced salivary and blood cortisol levels, self-perceived stress, anxiety, and overall job stress and job-related stress, respectively, after an 8-week intervention in a baseline-controlled study with highly stressed individuals [85; 86]. Finally, the only study assessing the effects of a psychobiotic diet was conducted in a sample of 21 males and females with poor dietary habits in a 4-week RCT. The findings indicated a significant decrease in perceived stress in the diet group (\(-32\%\) change from baseline) [72]. Additionally, _L. rhamnus_ HA-114 wasadministered in a RCT lasting 12 months involving 152 males and females with obesity under a weight loss program. The results showed a significant reduction in perceived stress over time in the probiotic group, although no significant group-by-time interaction effect was observed [73]. Conversely, several studies found no significant effects of psychobiotic treatment on stress biomarkers or self-reported psychological measures. One study reported that _L. rhamnous_ administration for 8 weeks failed to prevent the elevation of salivary cortisol output, anxiety measures, and stress measures following the SECPT in healthy male volunteers [74]. Similarly, _Bif. Longum_ administration for 16 weeks had no effect on salivary or hair cortisol levels and in stress or anxiety in healthy male volunteers undergoing academic stress in a double-blind, cross-over RCT [76]. Furthermore, no significant effects on anxiety were observed following 4 weeks of _L. helveticus_ supplementation in male and female participants [77] or 12-week treatment with a combination of omega-3 and various psychobiotics [80]. Additionally, in a study involving male and female patients diagnosed with major depression, 12 weeks of _L. Plantarum_ administration did not alter cortisol concentrations nor anxiety or stress levels [81]. Likewise, double-blind, cross-over RCT in healthy males and females experiencing stress-related symptoms after 19 weeks of Lactoflurene(r) treatment reported no significant effects [82]. Moreover, an additional study investigated urinary cortisol levels in a double-blind, cross-over RCT but did not observe significant differences between the psychobiotic and placebo groups [83]. Additional stress-related biomarkers were also evaluated. ACTH levels in blood were assessed in one study, but no significant differences among groups were found [75].