Can Low FODMAP Make You Constipated? Unpacking the Digestive Impact

November 24, 2025 •

4 min read

According to Monash University, a primary developer of the low FODMAP diet, many people who experience constipation as part of their Irritable Bowel Syndrome (IBS) still struggle with it during the elimination phase. It is a common, and sometimes unexpected, side effect for many following the diet, so the question 'can low FODMAP make you constipated?' is a very valid one.

Quick Summary

The low FODMAP diet can inadvertently lead to constipation by significantly reducing fiber and fluid intake. The elimination phase is restrictive, removing many high-fiber foods along with high FODMAPs. Key strategies to manage this include increasing low FODMAP fiber sources, prioritizing hydration, and staying active.

Key Points

Reduced Fiber Intake: The low FODMAP elimination phase removes many high-fiber foods, which can slow digestion and lead to constipation.
Less Water in the Bowel: Fewer osmotic FODMAPs and inadequate fluid intake can cause stools to become dry and hard to pass.
Gradual Fiber Increase: Consciously add low FODMAP, high-fiber foods like ground flaxseed, chia seeds, and kiwifruit to your diet slowly to avoid exacerbating symptoms.
Stay Hydrated: Increased fiber intake requires ample fluid to be effective, so prioritize drinking plenty of water.
Importance of Exercise: Regular physical activity helps stimulate the gastrointestinal muscles and promotes regular bowel movements.
Reintroduction is Key: The long-term goal of the diet is to reintroduce trigger-free high FODMAP foods, which can provide more dietary variety and fiber.
Consult a Professional: Working with a registered dietitian is crucial for navigating the diet safely and ensuring nutritional needs are met.

Why the Low FODMAP Diet Might Trigger Constipation

The low FODMAP diet is designed to reduce the intake of fermentable carbohydrates that can trigger IBS symptoms like gas, bloating, and diarrhea. However, a side effect of this restriction is that many high-fiber foods, such as wheat-based grains and legumes, are also high in FODMAPs and must be temporarily eliminated. This can result in a significant drop in a person's overall fiber intake, a primary cause of constipation.

Reduced Fiber Intake

Many high-FODMAP foods are also excellent sources of fiber. When these are removed, and not adequately replaced, dietary fiber levels can plummet.

Soluble Fiber: Absorbs water and forms a gel-like substance that softens stool. Eliminating high-FODMAP soluble fiber sources can leave stools dry and hard.
Insoluble Fiber: Adds bulk to stool and helps speed up its transit through the digestive system. Many high-FODMAP foods are also high in insoluble fiber.

Lowered Water Content in the Bowel

FODMAPs are osmotic, meaning they draw water into the large intestine. When high-FODMAP foods are avoided, the stools may contain less water, becoming drier and harder to pass, especially if fluid intake is not consciously increased.

Changes to Gut Bacteria

The gut microbiota relies on a variety of fermentable carbohydrates (FODMAPs) for fuel. During the restrictive elimination phase, the food sources for these bacteria are reduced, which can alter the gut microbiome and potentially affect bowel motility and regularity.

Other Potential Contributors

While the diet itself is a major factor, other issues can compound the problem. These include:

Insufficient overall food intake due to dietary restrictions.
A lack of physical activity, which helps stimulate bowel movements.
Certain medications or supplements that can have constipation as a side effect.

Strategies to Relieve and Prevent Constipation on a Low FODMAP Diet

Thankfully, constipation on a low FODMAP diet is manageable with the right approach. Incorporating low FODMAP, high-fiber alternatives and other lifestyle adjustments can help restore regular bowel movements.

Increase Your Fiber Intake with Low FODMAP Foods

Ground Flaxseed: Add 1–2 tablespoons to smoothies, oatmeal, or yogurt for a significant fiber boost.
Chia Seeds: A great source of fiber, chia seeds can be used to make puddings or sprinkled on other low FODMAP dishes.
Kiwifruit: Eating two kiwifruit per day is a well-researched method for improving constipation in people with IBS.
Brown Rice and Quinoa: Opt for these low FODMAP whole grains instead of refined options.
Low FODMAP Veggies: Include plenty of carrots, spinach, kale, green beans, and bell peppers in your meals.
Legumes: Canned lentils and chickpeas are low FODMAP in smaller, specific serving sizes if rinsed well.

Prioritize Hydration

Drinking enough water is crucial for keeping stool soft and preventing it from becoming hard and dry. Aim for light straw-colored urine throughout the day as a hydration guide. Fluid intake is especially important when increasing fiber, as fiber needs water to work effectively.

Stay Physically Active

Regular exercise stimulates the muscles in the digestive tract, which helps move food and waste along the intestines more efficiently. Even moderate activity like a daily walk can make a significant difference in promoting bowel regularity.

Consider the Reintroduction Phase

The elimination phase of the diet is not meant to be a permanent solution. If constipation persists after other measures, it might be a sign that it's time to move into the reintroduction phase. This process, done with the guidance of a dietitian, helps identify your personal triggers and allows for the reintroduction of higher FODMAP, potentially more fibrous foods.

Low FODMAP Fiber Sources: A Comparison Table


Low FODMAP Food	Serving Size (approx.)	Fiber Content (g)	Key Notes
Ground Flaxseed	1 tbsp (15g)	~5.2 g	Rich in soluble fiber, great for softening stool.
Chia Seeds	2 tbsp (24g)	~7 g	Excellent soluble fiber source. Can be used in many dishes.
Oats	1/2 cup (52g) raw	~5.5 g	A staple low FODMAP grain, rich in soluble fiber.
Quinoa	1 cup (155g) cooked	~5.5 g	A gluten-free whole grain alternative with high fiber.
Kiwifruit	2 small fruits	~4 g	Contains an enzyme that helps promote laxation.
Brown Rice	1 cup (180g) cooked	~3 g	Good source of insoluble fiber for adding bulk.

Conclusion: Finding the Right Balance

While the answer to 'can low FODMAP make you constipated?' is yes, it's a manageable issue with proper planning. The restrictive nature of the diet's elimination phase often reduces fiber and fluid, leading to slower transit and harder stools. The key is to consciously and gradually incorporate low FODMAP, high-fiber foods, prioritize hydration, and maintain an active lifestyle. Remember that the diet is a diagnostic tool, not a permanent eating plan, and working with a registered dietitian can provide personalized guidance for a smoother digestive journey. The goal is to identify your unique triggers and expand your diet as much as possible for long-term gut health. Learn more about the different phases of the low FODMAP diet from Monash University, the creators of the diet, for a better understanding of how to progress effectively.

Frequently Asked Questions

The low FODMAP diet can cause constipation primarily due to a reduction in fiber intake. Many high-FODMAP foods, like wheat and legumes, are also high in fiber. Removing these foods without conscious replacement can lead to harder, slower-moving stools.

Effective low FODMAP foods for constipation include ground flaxseed, chia seeds, kiwifruit, oats, quinoa, and certain vegetables like spinach and carrots. These foods are good sources of fiber and can help promote regular bowel movements.

To increase fiber, incorporate foods like ground flaxseed in smoothies, add chia seeds to oatmeal, and eat low FODMAP fruits like kiwis and oranges. Be sure to increase your fiber intake gradually to allow your digestive system to adjust.

Yes, some fiber supplements can be safe. Good options include psyllium husk, acacia fiber, and certain low FODMAP certified products. Consult with a dietitian before starting any new supplement.

Aim to drink enough water throughout the day to ensure your urine is a light, straw color. When increasing fiber, it is especially important to increase your fluid intake to keep stools soft and prevent potential blockage.

Yes, regular physical activity is very helpful. Exercise stimulates the muscles of the gastrointestinal tract, which encourages faster and more regular movement of waste through the intestines.

The elimination phase of the diet is short-term (typically 2-6 weeks). If constipation persists despite lifestyle adjustments, it may be a sign to move into the reintroduction phase with a dietitian's guidance.