Fiber is an important part of your daily diet. This is especially true for people living with irritable bowel syndrome (IBS), a gastrointestinal condition characterized by stomach cramps, diarrhea, and constipation. Because the body reacts differently to soluble and insoluble fiber, each type can help or harm.
Differences between soluble and insoluble fiber
Soluble fiber slows down processes in the digestive tract, helping with diarrhea, while insoluble fiber can speed up the process, relieving constipation.
“Soluble fiber is hydrophilic, so people may think of soluble fiber as a magnet for water,” says Melissa Majumdar, a senior bariatric dietitian in Boston.
By attracting water, soluble fiber removes excess fluid, which helps reduce diarrhea. Majumdar recommends that his IBS patients suffering from diarrheaincrease their intake of these soluble fiber-rich fruits and vegetables:
- Sweet potatoes
- Oats, beans, bran, and barley are also good sources of soluble fiber.
Insoluble fiber, on the other hand, does not dissolve in water, so it remains intact as it passes through your digestive system. “This is something that can be useful for constipation, because it adds volume to the stool and increases peristalsis, almost like a laxative effect.”
She advises her constipated patients to focus on adding more of these vegetables to their diet:
- Other foods rich in insoluble fiber include flaxseed, chia seeds, whole grains, bran, brown rice, cereals, and oats.
A meta-analysis published in September 2014 in the American Journal of Gastroenterology evaluated the use of dietary fiber supplements in 14 RCC studies involving 906 people living with IBS. The authors concluded that fiber supplementation-especially with psyllium, a soluble fiber — was effective in improving IBS symptoms compared to placebo.
According to a review published in September 2017 in the International Journal of Molecular Medicine, dietary fiber supplements appear to be safe, although if administered too quickly, they can lead to undesirable side effects, such as bloating.
However, Majumdar warns that supplements are considered functional fibers, meaning they may not be as beneficial as whole foods. Foods that have labels advertising “added fiber” are also forms of functional fiber and should be met with some skepticism.
“While they’re not harmful, we don’t know that they’re necessarily beneficial because they don’t have the same nutrients and biochemicals that whole foods would have, ” she says.
Increase fiber intake to relieve IBS symptoms
While dietary fiber can improve the function of your digestive system, a dramatic increase in intake can leave you feeling bloated when your body isn’t used to large amounts of fiber.
If you want to increase your fiber intake to better control IBS symptoms, Majumdar recommends adding fiber once a day and then waiting a few days a week to see how the body reacts. If all is well, you can continue to add more fiber to your diet.
“The first thing I would do is break down every meal and see where there is room to add fruit and vegetables, ” she says.
For example, instead of eating baked goods for breakfast, try Greek yogurt with fruit, nuts and flaxseed. For lunch and dinner, try adding salads, fruits and vegetables, and whole grains like brown rice, quinoa, and farro.
A good rule of thumb is to fill half your plate with fruits and vegetables, says Majumdar. Also, replace the peeled grains with whole grains. Instead of white bread, refined grains, and white rice, choose wholegrain bread, bran buns, oatmeal, wholegrain cereal, and brown rice.
Don’t forget to make these changes gradually for an easier transition.
And don’t forget to drink plenty of water. “Fiber can’t do its job without water. It can cause even more gastrointestinal distress if not combined with a liquid, ” says Majumdar. It is worth noting that fiber is not the only factor that affects the symptoms of IBS.