The standard treatment for chronic constipation is to eat a high fiber, plant-based diet. In 1969, Denis Burkitt showed that lack of fiber in the diet was associated with increased risk for diverticulosis, hemorrhoids and colorectal cancer (Lancet, 1969;294:1229–31), and today it is accepted that eating lots of dietary fiber in plant foods is healthful and helps to prevent heart attacks, strokes, certain cancers and premature death (Nutr Rev, 2009;67:188–205), as well as constipation.
However, other studies have shown that taking in large amounts of fiber can actually cause constipation in some people. In one study, constipated people on a high-fiber diet solved most of their constipation problems by going on a very low fiber diet (World J Gastroenterol, Sept 7, 2012;18(33):4593–4596). Doctors followed 63 people with an average age 47. They were all severely constipated, their doctors could not find a cause, they had normal colonoscopies to rule out disease, and had not had colon surgery. The participants ate no fiber for two weeks and then went on the diet of their choice: no-fiber, reduced-fiber, or high-fiber. Six months later, the 41 patients who stayed on a no-fiber diet and the 16 on a reduced-fiber diet had significant improvement in their symptoms:
• bowel frequency increased from one movement every 4.19 days to one movement per 1.9 days (compared to the high fiber dieters who had one movement every 6.43 days
• reduced symptoms of bloating
• reduced straining to pass stools
The six participants who had returned to a high-fiber diet had no change in their constipation.
Try Prunes First
Before you try a low-fiber diet to see if it will affect your constipation, at least give prunes a trial. Prunes contain soluble fiber and sorbitol, which produce gas that helps to push stool along (Pediatr Gastroenterol Hepatol Nutr, Dec 2014;17(4):203-208). They also contain a compound called chlorogenic acid that stimulates the muscles that line your intestines and colon to contract. To avoid excessive amounts of gas, take only two or three prunes at a time, and work up to five or more servings a day or as many as you need. A study of 120 healthy adults assigned them to groups that were given either 0, 10 or 15 prunes per day for four weeks (Clinical Nutrition, Feb 2019;38(1):165-173). Adding prunes to their diets increased:
• number of bowel movements to almost every day
• stool weight
• stool content of Bifidobacteria, healthful colon bacteria that reduce inflammation because they do not try to invade cells lining the colon
If you are chronically constipated and the standard treatments have not helped, you may want to try a low-fiber diet to see if this corrects your problem. Unfortunately, a low-fiber diet misses a lot of important nutrients that are found in vegetables, fruits and seeds (including legumes and whole grains), so I would not recommend it as a long-term diet. However, a trial could help you find out whether too much fiber is part of your constipation problem. You could then gradually re-introduce the healthful high-fiber foods and see what is the ideal balance for you.