Dietary protein residue can result in microbial generation of various toxic metabolites in the gut, such as ammonia. A prebiotic is "a substrate that is selectively utilised by host microorganisms conferring a health benefit". Prebiotics are carbohydrates that may have the potential to reverse the harmful effects of gut bacterial protein fermentation.

Three-stage continuous colonic model systems were inoculated with faecal samples from omnivore and vegetarian volunteers. Casein (equivalent to 105g protein consumption per day) was used within the systems as a fermentab274; le protein source. Two different doses of inulin type fructans (Synergy1) were later added (equivalent to 10g per day in vivo and 15g per day) to assess whether this influenced protein fermentation. Bacteria were enumerated by fluorescence in situ hybridisation with flow cytometry. Metabolites from bacterial fermentation (short chain fatty acid (SCFA), ammonia, phenol, indole and p-cresol) were monitored to further analyse proteolysis and the prebiotic effect. A significantly higher number of bifidobacteria was observed with the addition of inulin, together with reduction of Desulfovibrio spp. Furthermore, metabolites from protein fermentation such as branched chain fatty acids (BCFA) and ammonia were significantly lowered with Synergy1. Production of p-cresol varied among donors as we recognised four high producing models and two low producing models. Prebiotic addition reduced its production only in vegetarian high p-cresol producers.

Importance: Dietary protein levels are generally higher in Western populations than the world average. We challenged three-stage continuous colonic model systems containing high protein levels and confirmed the production of potentially harmful metabolites from proteolysis, especially replicates of the transverse and distal colon. Fermentations of proteins with a prebiotic supplementation resulted in a change in the human gut microbiota and inhibited the production of some proteolytic metabolites. Moreover, we observed both bacterial and metabolic differences between faecal bacteria from omnivore donors and vegetarian donors. Proteins with prebiotic supplementation showed higher Bacteroides spp. and inhibited clostridial cluster IX in omnivore models while in vegetarian modes, clostridial cluster IX were higher and Bacteroides spp. lowered with high protein plus prebiotic supplementation. Synergy1 addition inhibited p-cresol production in vegetarian high p-cresol producing models while the inhibitory effect was not seen in omnivore models.

膳食中的蛋白质残留会导致肠道中各种微生物如氨的有毒代谢产物的产生。益生元是“被宿主微生物选择性利用的赋予健康的底物”。益生元是碳水化合物，可能具有逆转肠道细菌蛋白质发酵的有害作用的潜力。

三阶段连续结肠模型系统接种了杂食动物和素食志愿者的粪便样本。酪蛋白（相当于每天105g蛋白质消耗量）在系统中用作fermentab274；蛋白质来源。随后添加两种不同剂量的菊粉型果聚糖（Synergy1）（相当于体内每天10g和每天15g）来评估这是否影响蛋白质发酵。通过流式细胞术通过荧光原位杂交对细菌进行计数。细菌发酵产生的代谢产物（短链脂肪酸（SCFA），氨，苯酚，吲哚和p-甲酚）被监测以进一步分析蛋白水解和益生元的作用。加入菊粉后，双歧杆菌的数量明显增加，同时Desulfovibrio spp减少。此外，Synergy1可显着降低蛋白质发酵产生的代谢产物，例如支链脂肪酸（BCFA）和氨。对位甲酚的生产因捐助者而异，因为我们认识到四种高产模式和两种低产模式。益生元的添加仅在素食高对甲酚生产者中降低了其产量。

重要性：西方人群的饮食蛋白质水平通常高于世界平均水平。我们挑战了包含高蛋白水平的三阶段连续结肠模型系统，并确认了蛋白水解产生潜在有害的代谢产物，尤其是横结肠和远端结肠的复制。补充益生元的蛋白质发酵会导致人类肠道菌群发生变化，并抑制某些蛋白水解代谢产物的产生。此外，我们观察到杂食性供体和素食供体的粪便细菌之间的细菌和代谢差异。补充了益生元的蛋白质显示出更高的杀菌剂spp。并在杂食动物模型中抑制了梭菌丛IX，而在素食模式下，梭菌丛IX较高，而拟杆菌属则较高。降低高蛋白加益生元补充剂。Synergy1的添加在素食高对甲酚生产模型中抑制了对甲酚的生产，而在杂食动物模型中未见抑制作用。