A phase I–II clinical trial showed that the Immunoglobulin G positive restricted diet (IgG res diet) and the cold/spicy/fried restricted diet (CSF res diet) both effectively alleviated symptoms in irritable bowel syndrome with diarrhea (IBS-D) patients. The IgG res diet was a crucial means for precisely excluding particular items. If intolerant foods cannot be completely avoided, avoiding raw, chilled, hot, fried, and alcoholic foods is a wise move. The best choice is using a probiotic together with IgG food elimination.

To treat IBS-D patients, Xian-Shu Zhao et al. compared the CSF res diet with the IgG res diet and investigated how well the diets worked when paired with a probiotic. In Phase I, subjects were randomly assigned to one of four diets: control, CSF res diet, IgG res diet, and a combination of both diets (CSF + IgG res diet). Patients were randomly assigned to the IgG res diet plus placebo or the IgG res diet with probiotics in phase II. Both treatments lasted for 12 weeks. IgG titer and the IBS-D Symptom Severity Scale (IBS-D-SSS) were measured at the start and conclusion of the trial.

The two parts of the study (Phase I and II) were completed by 214 and 167 participants, respectively. IBS-D-SSS and total positive IgG (TIgG) grade considerably enhanced post-intervention contrasted to baseline, with outcomes comparable to the control group. Reductions in IBS-D-SSS and TIgG grades were noted and substantially varied among the groups. There were few outliers, however; neither IBS-D-SSS nor TIgG grades showed any changes between the CSF res diet, IgG res diet, or CSF + IgG res diet.

There were some cases where no notable distinctions were found. Between IgG res diet and CSF + IgG res diet, there were no significant differences witnessed in terms of IBS-D-SSS. Additionally, there were no noteworthy variations in TIgG grade among the CSF res diet, IgG response diet, and CSF plus IgG res diet. On the other hand, the CSF res diet and IgG res diet exhibited a synergistic impact, leading to a reduction in both IBS-D-SSS and TIgG  titer. The IgG res diet played a more pivotal role in this combined effect.

The IBS-D-SSS and TIgG grade reduced from baseline when the IgG res diet was assessed using either a placebo or probiotic. The probiotic considerably reduced IBS-D-SSS, although there was no appreciable difference in TIgG grade between the IgG diet + placebo and the IgG diet + probiotic. Even though IgG res diet had more contribution, both CSF res diet and IgG res diet mitigated IBS symptoms and showed synergy. A better approach is to avoid raw, cold, spicy, fried, and alcoholic meals when intolerant foods cannot be completely excluded from a diet. The best diet was the IgG res diet with Bifidobacteria, which may work via a non-IgG pathway.