In IBS with constipation (IBS-C), hard or lumpy stools (Bristol types 1 and 2) dominate on days when bowel movements aren't normal, along with the abdominal pain that defines IBS.[1] Diet helps in two ways. Soluble fiber and enough fluid keep stools softer and easier to pass,[2] while avoiding fibers that produce a lot of gas, such as wheat bran and inulin, limits the bloating and discomfort a sensitive gut reacts to.[3]
Should I avoid fiber if I have IBS-C?
No, but choose the type carefully. Monash University's dietitians point out that most people with IBS eat too little fiber, which may make constipation and abdominal pain worse.[4] UK advice is to increase fiber if constipation is your main problem,[5] but to favor soluble fiber, such as psyllium (ispaghula) and oats, over insoluble fiber such as bran.[6] Trials back this up: soluble fiber improves IBS symptoms, while bran shows no clear benefit[7] and was the fiber people were most likely to give up early because their symptoms got worse.[8] Increase fiber gradually to limit extra gas and bloating.[9] Our guide to IBS trigger foods covers the fiber evidence in more detail.
What foods help IBS-C?
| Food or supplement | What the evidence shows | Tips |
|---|---|---|
| Psyllium (ispaghula) | More people improved than on placebo in a primary-care trial (57% vs 35% in the first month)[8]; a recommended first-line treatment for IBS[9] | Take it with plenty of water and build up slowly[2][3] |
| Kiwifruit | In a multinational crossover trial, two green kiwifruit a day for four weeks added about 1.7 complete bowel movements a week in people with IBS-C and improved abdominal comfort[10]; an earlier small trial found faster colon transit[11] | A low-FODMAP fruit in normal servings[4] |
| Oats | A food source of soluble fiber recommended in UK guidance[6] | Porridge or an oat-based cereal |
| Linseeds (flaxseeds) | Mixed: NICE suggests them for wind and bloating,[6] but a small trial found no clear benefit over no linseeds[12] | Monash says they may help constipation, though more studies are needed[3] |
| Other low-FODMAP, high-fiber foods | Oranges, carrots, quinoa, brown rice, firm tofu, nuts, chia seeds and potatoes with the skin on add fiber at low-FODMAP servings[4] | Spread vegetables across at least two meals or snacks[2] |
| Wheat bran | No clear benefit, and it may make IBS symptoms worse[9][3] | Best avoided |
Some soluble-fiber foods often suggested for constipation, such as beans and lentils,[13] are high in FODMAPs, although small servings of canned lentils or chickpeas are low in FODMAPs.[2] The same goes for fruit: apples, pears, stone fruits and dried fruit are high in FODMAPs, while kiwifruit, blueberries and citrus fruits are lower-FODMAP choices.[14]
How much should I drink, and what else helps?
Fiber works best with enough fluid. NICE advises at least 8 cups of fluid a day, mainly water or non-caffeinated drinks,[6] and Monash stresses that fluid matters even more if you take soluble fiber supplements or osmotic laxatives.[2] Coffee stimulates the colon about as strongly as a meal,[15] but NICE suggests keeping tea and coffee to 3 cups a day.[6]
Regular activity helps too. In a trial, people with IBS who increased their physical activity for 12 weeks had a bigger drop in symptom scores than those who kept to their usual routine.[16] On the toilet, give yourself enough time, avoid straining, and try leaning forward with your forearms on your thighs and your feet raised on a small footstool.[4] Logging stool form on the Bristol stool chart shows whether a change is working; an app such as IBS Clue keeps that log alongside your meals.
Does the low-FODMAP diet help IBS-C?
It may ease pain and other symptoms, as it does in IBS generally,[9] but it rarely fixes constipation on its own. Monash notes that people with IBS-C often find a low-FODMAP diet alone doesn't relieve their symptoms enough.[2] Fiber is part of the reason. Wheat, rye, barley and legumes are major fiber sources,[3] and some studies show fiber intake falls during the strict phase of the diet.[17] In one study, constipation didn't improve when the diet was led by a physician without a dietitian, possibly because patients weren't shown how to keep their fiber up.[17] If you try it, plan your fiber from the start, ideally with a dietitian; see our low-FODMAP diet guide.
What causes IBS-C?
As with other types of IBS, there isn't a single cause. An oversensitive gut, the gut-brain connection, changes in gut bacteria and genes are all thought to contribute, and the mix varies from person to person.[5] Diet can make things worse: too little fiber may aggravate constipation and pain,[4] and drinking too little makes stools harder to pass.[2] Abdominal pain is what separates IBS-C from ordinary constipation; without it, the diagnosis isn't IBS.[1]
When should I see a doctor about IBS constipation?
See your doctor if diet changes and pharmacy remedies aren't helping.[13] Laxatives are a standard next step. NICE recommends considering them but advises against lactulose, which can cause bloating, and the BSG says polyethylene glycol (PEG) may help constipation in IBS.[6][5][9] Prescription medicines are available if laxatives haven't worked.[6] See a doctor promptly for warning signs such as blood in your stool, unexplained weight loss, anemia, a lump in your abdomen, or symptoms that first start after about age 50.[18] More in IBS red flags.