What to Know About Fiber if You Have IBS With Constipation

Fiber is a must for regular bowel movements. But if you have irritable bowel syndrome with constipation (IBS-C), you might worry that filling up on fiber could worsen symptoms such as cramps, gas, and bloating — and make constipation even worse.

Used correctly, though, fiber can be a useful tool for managing your IBS-C symptoms. “Getting enough dietary fiber from various foods can help manage constipation and support a healthy gut microbiome,” says Elisabeth Moore, RD, a registered dietitian at Beth Israel Deaconess Medical Center in Boston.

The trick is choosing the right high-fiber foods — namely, those that feel good for your body and don’t trigger your symptoms. Here’s what to know about making fiber work for you.

There are two types of fiber, both of which help regulate digestion and bowel movements:

• Soluble fiber: This type of fiber dissolves in water to form a gel-like material that slows digestion and helps soften the stool. You can find it in foods like apples, oranges, grapefruit, vegetables, lentils, peas, barley, oats, and oat bran.
• Insoluble fiber: This type of fiber does not dissolve in water. It helps move food through the digestive system and adds bulk to your stool, promoting regular bowel movements. You can find it in foods like fruits with edible peels and seeds, vegetables, whole-grain products (such as whole-wheat bread or pasta), stone-ground cornmeal, oats, buckwheat, and brown rice.

The downside? If you overdo it, too much fiber (of either kind) can end up making your GI symptoms worse, Moore says. So, you might need to experiment to find your sweet spot. It may also take some trial and error to find which sources of fiber are easiest for you to tolerate.

As you increase your fiber intake, go slow. This will give your digestive system time to adjust over the course of several weeks. Adding too much fiber to your diet all at once is a recipe for more gas, bloating, and constipation. Up your fiber intake (particularly the soluble kind) by just a few grams at a time, then wait a few days before adding a bit more.

Be sure to drink plenty of water too, Moore recommends. Fiber absorbs fluids as it passes through your GI tract, and not drinking enough water can make it even harder to have a bowel movement.

If you aren’t sure which FODMAPs are problematic for you, a registered dietitian who specializes in IBS can help.

It’s best to discuss fiber supplements with your dietitian or doctor to figure out if they are needed and which ones may be most useful for you, Moore says.

Many people with IBS-C find that soluble fiber sources are gentler on their systems than insoluble fiber sources. Some good options to try include:

• Avocado
• Bananas
• Barley
• Cabbage
• Chickpeas
• Oatmeal
• Oranges
• Root vegetables (like carrots, parsnips, or sweet potato)
• Strawberries

Use these foods as a starting point, and experiment with different portion sizes and prep methods to see what feels good for you, recommends Moore. For example, if a big bowl of black bean soup makes you gassy, try a small cup instead. Thoroughly cooking fruits and vegetables — think steaming or roasting — can make them easier to tolerate too, she adds.

• Getting enough fiber can make it easier to manage IBS-C symptoms, though soluble fiber may be easier to tolerate than insoluble fiber.
• It’s important to increase your fiber intake gradually and drink plenty of water as you do.
• Don’t fill up on fiber all at once. Stick to smaller portion sizes and opt for cooked fruits and vegetables rather than raw ones.