NIHR Nottingham Biomedical Research Centre, Nottingham University Hospitals NHS Trust and the University of Nottingham, Nottingham, United Kingdom.
Nottingham Digestive Diseases Centre, School of Medicine, University of Nottingham, Nottingham, United Kingdom.
Am J Clin Nutr. 2020 Sep 1;112(3):595-602. doi: 10.1093/ajcn/nqaa173.
Wheat bran, nopal, and psyllium are examples of particulate, viscous and particulate, and viscous fibers, respectively, with laxative properties yet contrasting fermentability.
We assessed the fermentability of these fibers in vitro and their effects on intestinal function relevant to laxation in vivo using MRI.
Each fiber was predigested prior to measuring gas production in vitro during 48-h anaerobic incubation with healthy fecal samples. We performed a randomized, 3-way crossover trial in 14 healthy volunteers who ingested 7.5 g fiber twice on the day prior to study initiation and once with the study test meal. Serial MRI scans obtained after fasting and hourly for 4 h following meal ingestion were used to assess small bowel water content (SBWC), colonic volumes, and T1 of the ascending colon (T1AC) as measures of colonic water. Breath samples for hydrogen analysis were obtained while patients were in the fasted state and every 30 min for 4 h following meal ingestion.
In vitro, the onset of gas production was significantly delayed with psyllium (mean ± SD: 14 ± 5 h) compared with wheat bran (6 ± 2 h, P = 0.003) and was associated with a smaller total gas volume (P = 0.01). Prefeeding all 3 fibers for 24 h was associated with an increased fasting T1AC (>75% of values >90th centile of the normal range). There was a further rise during the 4 h after psyllium (0.3 ± 0.3 s P = 0.009), a fall with wheat bran (-0.2 ± 0.2 s; P = 0.02), but no change with nopal (0.0 ± 0.1 s, P = 0.2). SBWC increased for all fibers; nopal stimulated more water than wheat bran [AUC mean (95% CI) difference: 7.1 (0.6, 13.8) L/min, P = 0.03].Breath hydrogen rose significantly after wheat bran and nopal but not after psyllium (P < 0.0001).
Both viscous and particulate fibers are equally effective at increasing colonic T1 over a period of 24 h. Mechanisms include water trapping in the small bowel by viscous fibers and delivery of substrates to the colonic microbiota by more fermentable particulate fiber. This trial was registered at clinicaltrials.gov as NCT03263065.
麦麸、仙人掌和车前草分别是颗粒状、粘性和颗粒状粘性纤维，具有通便作用，但发酵能力不同。
我们使用 MRI 评估这些纤维在体外的发酵能力及其对体内通便相关的肠道功能的影响。
将每种纤维进行预消化，然后在 48 小时的厌氧孵育过程中，与健康粪便样本一起测量气体生成。我们在 14 名健康志愿者中进行了一项随机、三向交叉试验，他们在研究开始前的两天每天摄入 7.5 克纤维两次，并在研究测试餐中摄入一次。空腹后进行连续 MRI 扫描，并在进食后 4 小时内每小时进行一次扫描，以评估小肠水含量 (SBWC)、结肠容量和升结肠 T1（T1AC），作为结肠水的测量指标。在禁食状态下和进食后 4 小时内每 30 分钟采集一次呼吸样本进行氢分析。
在体外，车前草（14 ± 5 小时）的气体生成起始时间明显晚于麦麸（6 ± 2 小时，P = 0.003），且总气体体积较小（P = 0.01）。预喂食所有 3 种纤维 24 小时与空腹 T1AC 升高（超过 90%正常值范围的 75%以上）有关。在喂食车前草后的 4 小时内，T1AC 进一步升高（0.3 ± 0.3 s，P = 0.009），麦麸则降低（-0.2 ± 0.2 s，P = 0.02），但仙人掌纤维没有变化（0.0 ± 0.1 s，P = 0.2）。所有纤维的 SBWC 均增加，仙人掌纤维刺激的水量多于麦麸纤维[AUC 平均值（95%CI）差值：7.1（0.6，13.8）L/min，P = 0.03]。麦麸和仙人掌纤维后呼吸氢显著升高，但车前草纤维后无显著升高（P < 0.0001）。
粘性纤维和颗粒状纤维在 24 小时内均可同等有效地增加结肠 T1。其机制包括粘性纤维在小肠中捕获水分，以及更可发酵的颗粒状纤维向结肠微生物群提供底物。该试验在 clinicaltrials.gov 上注册，编号为 NCT03263065。
