“…Among all the psychiatric symptoms, emotional symptoms, especially anxiety symptoms, are the most ideal targets of probiotics because anxiety is closely related to GI symptoms, such as stomachaches, constipation, or diarrhea (Haug, Mykletun, & Dahl, 2002). For example, some studies reported (Guyonnet et al, 2007;Lorenzo-Zuniga et al, 2014;Silk, Davis, Vulevic, Tzortzis, & Gibson, 2009;Williams et al, 2009) that probiotics are superior to placebo in alleviating anxiety, while others (Begtrup, de Muckadell, Kjeldsen, Christensen, & Jarbol, 2013;Lyra et al, 2016;Simren et al, 2010;Stevenson, Blaauw, Fredericks, Visser, & Roux, 2014) found no significant difference between probiotics and placebo. Thus, with the above theoretical basis derived from the findings of animal studies, many clinical trials have been implemented to test the effect of probiotics on anxiety either in healthy subjects or in subjects with mental or physical illness.…”