If you eat more fiber, should you also drink more water? Original paper

Among participants with low fiber intake, increasing both fiber and water intake resulted in fewer unpleasant abdominal symptoms and similar effects on bowel function, compared to increasing only fiber intake.

This Study Summary was published on June 28, 2022.


For people with a low-fiber diet, increasing fiber intake is often recommended for a variety of reasons, including improving bowel function. Dietary fiber binds water in the gastrointestinal tract, meaning that increasing water and fiber intake may have synergistic effects on gut health compared to increasing fiber intake alone.

The study

In this 2-week randomized controlled trial, 20 participants (mean age of 31) with a habitually low daily fiber intake (below 15 grams for women, below 22.8 grams for men) were assigned to either increase their fiber intake or increase both their fiber and water intake. Female participants added 13 grams of fiber and male participants added 20 grams of fiber in the form of powdered wheat bran, pectin, and green banana. For participants who increased their water intake, 2 liters of mineral water were provided for daily consumption.

The primary outcome was bowel habits, including number of defecations, amount of straining during defecation, and stool consistency. The secondary outcomes were stool characteristics, urine output, abdominal complaints, and fecal microbiota.

The results

Both groups experienced a similar increase in weekly bowel movements (fiber only: from 6.8 to 8.8 per week; fiber + water: from 8.6 to 10 per week). Other bowel outcomes did not change. Urinary output was higher in the fiber+water group compared to the fiber only group.

The incidence of any new abdominal symptoms (e.g., pain, flatulence, bloating) was higher in the fiber only group compared to the fiber+water group (9 versus 3).

Fecal microbiota displayed several differences between groups, including higher levels of Bifidobacterium, Faecalibacterium prausnitzii, and Bacteroides+Prevotella in the fiber+water group compared to the fiber only group.


The participants in this trial were described as “friends and coworkers” of the investigators

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This Study Summary was published on June 28, 2022.