Background. Functional dyspepsia is characterized by symptoms that apparently originate in the stomach without detectable cause by conventional diagnosis test. The pathophysiology of functional dyspepsia is not known, but a number of data indicate that dyspeptic patients have increased sensitivity of the digestive system, so that physiological stimuli may induce their symptoms. Some patients with functional dyspepsia have also functional constipation and the investigators hypothesize that in them constipation triggers or facilitates dyspeptic symptoms, and consequently, correction of constipation relieves dyspeptic symptoms.

Objective. To demonstrate the superiority of biofeedback versus a fiber supplement for the treatment of dyspeptic symptoms in patients with constipation due to functional outlet obstruction.

Design. Randomized, controlled parallel trial performed in a referral center. Participants. Consecutive patients complaining of symptoms of functional dyspepsia and functional outlet obstruction.

Interventions: Patients will be assigned to experimental (biofeedback for functional outlet obstruction) and active comparator (fiber supplementation) arms. Biofeedback for functional outlet obstruction: sessions of biofeedback guided by anorectal manometry (performed during the first 3 weeks of the intervention period) combined with instructions for daily exercising for 4 weeks. Fiber supplementation: 2.5 g plantago ovata per day for 4 weeks. Main outcome and measures. Clinical symptoms of functional dyspepsia measured by daily questionnaires for 7 consecutive days before and during the last week of intervention.

Relevance. Functional Dyspepsia, defined by purely clinical criteria, brings together a diverse group of conditions with different pathophysiology. As a result, the treatment is empirical and globally inefficient. This study will identify a subset of patients with a common pathophysiological mechanism of dyspeptic symptoms (functional outlet obstruction) which respond to specific treatment (biofeedback).

Patients with functional dyspepsia and functional constipation.

Inclusion Criteria

• Rome IV criteria for functional dyspepsia type of postprandial distress syndrome.
• Rome IV criteria of functional constipation
• Anorectal manometry showing defective sphincter relaxation during the defecatory manoeuver.

Exclusion Criteria:

• History of organic gastrointestinal disorders
• Cognitive impairment.