Twenty healthy volunteers had their baseline parameters (symptoms, bowel habit, quality of life, fecal characteristics and microbiota) measured during a week of monitoring followed by randomization to a 14 days course of increased fiber in diet or increased fiber and water intake, with repetition of parameters measuring at the end.

Demographic and clinical data were collected and recorded in the first interview after signing the informed consent. The protocol was composed of two phases. The baseline phase lasted 7 days, when participants reported their usual diet on a food dairy in the first 3 days, between Sunday and Tuesday. Calculation of nutrient intake was performed using ADS nutri software (UFPEL, Pelotas, Brazil). Participants approved for the next phase were then randomized to fiber and fiber+water groups, which lasted 14 days. During this period participants were asked to report their intestinal habits including bowel movements, graduation of straining and subjective stool consistency. Participants were instructed to rank straining using a Likert scale from 1 (minimum) to 5 (maximum), and the Bristol scale for stool consistency. In the last day of treatment phase (Saturday) participants collected feces and urine of 24 hours, and responded a symptoms questionnaire. Food and liquid intake were recorded on a diary during the last 3 days of treatment for comparison with the baseline phase stage.

Inclusion Criteria:

• non-obese
• absence of abdominal complaints

Exclusion Criteria:

• use of medications that interfere with the gastrointestinal tract function
• past of abdominal surgery
• any acute or chronic disease