The importance of dietary fiber (DF) in animal diets is increasing with the advancement of nutritional research. DF is fermented by gut microbiota to produce metabolites, which are important in improving intestinal health. This review is a systematic review of DF in pig nutrition using in vitro and in vivo models. The fermentation characteristics of DF and the metabolic mechanisms of its metabolites were summarized in an in vitro model, and it was pointed out that SCFAs and gases are the important metabolites connecting DF, gut microbiota, and intestinal health, and they play a key role in intestinal health. At the same time, some information about host-microbe interactions could have been improved through traditional animal in vivo models, and the most direct feedback on nutrients was generated, confirming the beneficial effects of DF on sow reproductive performance, piglet intestinal health, and growing pork quality. Finally, the advantages and disadvantages of different fermentation models were compared. In future studies, it is necessary to flexibly combine in vivo and in vitro fermentation models to profoundly investigate the mechanism of DF on the organism in order to promote the development of precision nutrition tools and to provide a scientific basis for the in-depth and rational utilization of DF in animal husbandry. KEY POINTS: • The fermentation characteristics of dietary fiber in vitro models were reviewed. • Metabolic pathways of metabolites and their roles in the intestine were reviewed. • The role of dietary fiber in pigs at different stages was reviewed.

OBJECTIVE: Abdominal distention results from abdominophrenic dyssynergia (ie, diaphragmatic contraction and abdominal wall relaxation) in patients with disorders of gut-brain interaction. This study aimed to validate a simple biofeedback procedure, guided by abdominothoracic wall motion, for treating abdominal distention.
METHODS: In this randomized, parallel, placebo-controlled trial, 42 consecutive patients (36 women and 6 men; ages 17-64 years) with meal-triggered visible abdominal distention were recruited. Recordings of abdominal and thoracic wall motion were obtained using inductance plethysmography via adaptable belts. The signal was shown to patients in the biofeedback group, who were taught to mobilize the diaphragm. In contrast, the signal was not shown to the patients in the placebo group, who were given a placebo capsule. Three sessions were performed over a 4-week intervention period, with instructions to perform exercises (biofeedback group) or to take placebo 3 times per day (control group) at home. Outcomes were assessed through response to an offending meal (changes in abdominothoracic electromyographic activity and girth) and clinical symptoms measured using daily scales for 7 days.
RESULTS: Patients in the biofeedback group (n = 19) learned to correct abdominophrenic dyssynergia triggered by the offending meal (intercostal activity decreased by a mean ± SE of 82% ± 10%, anterior wall activity increased by a mean ± SE of 97% ± 6%, and increase in girth was a mean ± SE of 108% ± 4% smaller) and experienced improved clinical symptoms (abdominal distention scores decreased by a mean ± SE of 66% ± 5%). These effects were not observed in the placebo group (all, P < .002).
CONCLUSIONS: Abdominothoracic wall movements serve as an effective biofeedback signal for correcting abdominophrenic dyssynergia and abdominal distention in patients with disorders of gut-brain interaction. ClincialTrials.gov, Number: NCT04043208.

Patients with functional dyspepsia are believed to have increased sensitivity of the gastrointestinal tract, and some also have functional constipation. We investigated whether in patients with functional dyspepsia, correction of dyssynergic defecation can reduce postprandial fullness.
We performed a parallel trial at 2 referral centers in Spain, from June 2016 through January 2018 of 50 patients who fulfilled the Rome IV criteria for functional dyspepsia with postprandial distress syndrome and functional constipation and dyssynergic defecation. After a 2-week pretreatment phase, the patients were randomly assigned to groups that learned to correct dyssynergic defecation (2-3 sessions of biofeedback combined with instructions for daily exercise; n = 25) or received dietary fiber supplementation (3.5 g plantago ovata per day; n = 25) for 4 weeks. The primary outcome was change in postprandial abdominal fullness, measured daily on a scale of 0-10, during the last 7 days treatment phase vs the last 7 days of the pretreatment phase. Anal gas evacuations were measured (by an event marker) during the last 2 days of the pretreatment vs treatment phases.
Biofeedback treatment corrected dyssynergic defecation in 19/25 patients; corrected dyssynergic defection reduced postprandial fullness by 22%±1% in these patients (P < .001), and reduced the number of anal evacuations by 21%±8% (P = .009). Fiber supplementation did not reduce postprandial fullness or anal evacuations (P ≤ .023 between groups for both parameters in the intent to treat analysis).
Diagnosis and correction of dyssynergic defecation reduces dyspeptic symptoms by more than 20% in patients with functional dyspepsia and associated constipation. Dietary fiber supplementation does not reduce symptoms in these patients. ClinicalTrials.gov no: NCT02956187.

OBJECTIVE: Abdominal distention is produced by abnormal somatic postural tone. We developed an original biofeedback technique based on electromyography-guided control of abdominothoracic muscular activity. We performed a randomized, placebo-controlled study to demonstrate the superiority of biofeedback to placebo for the treatment of abdominal distention.
METHODS: At a referral center in Spain, we enrolled consecutive patients with visible abdominal distention who fulfilled the Rome III criteria for functional intestinal disorders (47 women, 1 man; 21-74 years old); 2 patients assigned to the placebo group withdrew and 2 patients assigned to biofeedback were not valid for analysis. Abdominothoracic muscle activity was recorded by electromyography. The patients in the biofeedback group were shown the signal and instructed to control muscle activity, whereas patients in the placebo received no instructions and were given oral simethicone. Each patient underwent 3 sessions over a 10-day period. The primary outcomes were subjective sensation of abdominal distention, measured by graphic rating scales for 10 consecutive days before and after the intervention.
RESULTS: Patients in the biofeedback group effectively learned to reduce intercostal activity (by a mean 45% ± 3%), but not patients in the placebo group (reduced by a mean 5% ± 2%; P < .001). Patients in the biofeedback group learned to increase anterior wall muscle activity (by a mean 101% ± 10%), but not in the placebo group (decreased by a mean 4% ± 2%; P < .001). Biofeedback resulted in a 56% ± 1% reduction of abdominal distention (from a mean score of 4.6 ± 0.2 to 2.0 ± 0.2), whereas patients in the placebo group had a reduction of only 13% ± 8% (from a mean score of 4.7 ± 0.1 to 4.1 ± 0.4) (P < .001).
CONCLUSIONS: In a randomized trial of patients with a functional intestinal disorder, we found that abdominal distention can be effectively corrected by biofeedback-guided control of abdominothoracic muscular activity, compared with placebo. ClincialTrials.gov no: NCT01205100.