Does Eating a Lot of Protein Affect Your Bowels? Understanding the Digestive Impact

November 3, 2025 •

4 min read

According to the American Journal of Clinical Nutrition, participants on high-protein, low-carbohydrate diets often report increased intestinal discomfort and reduced stool frequency. So, does eating a lot of protein affect your bowels? The answer is that protein itself is not the primary cause of digestive problems, but related factors often associated with high-protein diets can significantly impact bowel function.

Quick Summary

A high-protein diet can affect bowel movements, often causing constipation due to low fiber and inadequate hydration. Some protein sources may also cause diarrhea. The impact depends on balancing protein intake with fiber, fluids, and healthy gut bacteria.

Key Points

High protein alone is not the issue: Bowel problems on high-protein diets are typically caused by insufficient dietary fiber and water intake, not the protein itself.
Constipation often stems from low fiber: A heavy focus on animal protein, which contains no fiber, often replaces fiber-rich plant foods, leading to hard, sluggish stools.
Hydration is vital for digestion: A high-protein intake increases the body's need for water. Inadequate hydration can dehydrate the colon, causing constipation.
Diarrhea can be caused by supplements: Dairy-based protein powders can trigger loose stools in lactose-intolerant individuals, while artificial sweeteners in supplements can have a laxative effect.
Protein source matters for gut health: Plant-based proteins contain fiber that feeds beneficial gut bacteria, whereas high animal protein with low fiber can alter the gut microbiome negatively.
Balance is the solution: To prevent bowel issues, pair protein with high-fiber foods, drink plenty of water, and ensure a diverse diet.

While protein is a crucial macronutrient for muscle growth, satiety, and overall health, a drastic increase in protein consumption can significantly alter your bowel habits. The digestive system thrives on balance, and when a high-protein diet displaces other vital components like dietary fiber and adequate hydration, unwanted side effects can occur.

The Link Between High Protein and Constipation

Contrary to popular belief, protein itself does not cause constipation. The problem typically arises when high-protein diets, especially those emphasizing animal products and limiting carbohydrates, inadvertently reduce the intake of fiber-rich plant foods.

The Low-Fiber Conundrum

Dietary fiber is the non-digestible part of plant foods that is essential for healthy bowel function. It adds bulk to stool, which helps it move more easily through the intestines. Insoluble fiber, found in nuts, seeds, and leafy greens, adds bulk, while soluble fiber, present in oats, beans, and certain fruits, softens the stool by absorbing water. When following a diet heavy in animal proteins like meat, poultry, and fish, which contain zero fiber, it's easy to fall short of the recommended daily fiber intake, leading to hard, difficult-to-pass stools.

The Role of Hydration

Proper hydration is critical for the digestive process, especially when consuming more protein. Protein metabolism produces urea and other waste products that are filtered by the kidneys and excreted through urine, increasing the body's need for water. Without enough fluid, the colon compensates by absorbing more water from waste, resulting in dry, compact stools that contribute to constipation. Staying hydrated ensures fiber can work effectively to soften stool and facilitate smooth transit through the digestive tract.

Can Too Much Protein Cause Diarrhea?

While constipation is a more common complaint, some individuals may experience loose stools or diarrhea on a high-protein diet due to specific triggers.

Lactose Intolerance and Protein Supplements

Many protein powders and supplements are derived from dairy products, like whey and casein. For those with lactose intolerance, consuming these products can lead to gastrointestinal symptoms such as gas, bloating, and diarrhea. Even if a person can tolerate some dairy, a sudden increase in intake can overwhelm their digestive system and cause a reaction.

Artificial Sweeteners and Additives

Protein bars and shakes often contain artificial sweeteners and sugar alcohols (such as xylitol and mannitol) to keep the calorie count low. These ingredients are not fully absorbed by the body and can have a laxative effect, drawing water into the colon and causing diarrhea, particularly in large doses.

Undigested Protein and the Gut Microbiome

Excessive protein intake, especially from poorly digested sources, can lead to undigested protein reaching the large intestine. The gut microbiota then ferment this protein, producing potentially toxic metabolites like ammonia, phenols, and amines. This can lead to a less diverse and more unbalanced gut microbiome, which can disrupt normal digestive function and trigger symptoms like loose stools.

Protein Sources: Animal vs. Plant-Based

The source of your protein plays a significant role in how it affects your bowels. A diverse approach that includes both animal and plant-based proteins is often the best strategy for maintaining digestive health.


Feature	Animal-Based Protein	Plant-Based Protein (e.g., legumes, nuts)
Fiber Content	None	High in fiber (both soluble and insoluble)
Saturated Fat	Often higher, especially in red meat and full-fat dairy	Lower or absent
Microbiome Impact	Can reduce beneficial bacteria populations and increase harmful metabolites if fiber intake is low	Feeds beneficial gut bacteria, promoting diversity and resilience
Digestibility	Highly digestible, but lacks fiber to aid transit	Can be harder to digest for some individuals, especially with conditions like IBS, but contains essential fiber

Strategies to Maintain Healthy Bowels on a High-Protein Diet

Successfully following a high-protein diet without digestive issues requires a balanced approach. Here are some actionable strategies:

Prioritize fiber: Actively seek out high-fiber foods to pair with your protein. Aim for at least 25-38 grams of fiber daily from sources like fruits, vegetables, whole grains, nuts, and legumes.
Increase hydration: Drink at least 8-10 glasses of water daily. Increase your fluid intake as your protein consumption rises to help your kidneys filter waste and keep stool soft.
Choose plant-based proteins: Incorporate more plant-based protein sources like lentils, chickpeas, tofu, and beans, which offer the dual benefits of protein and fiber.
Use caution with supplements: If you rely on protein shakes or bars, be mindful of their ingredients. Choose brands without excessive artificial sweeteners or opt for a simple protein powder mixed with water.
Add probiotics: Include fermented foods like yogurt, kefir, or kimchi in your diet, or consider a probiotic supplement. This can support a healthy gut microbiome and aid digestion.
Don't forget exercise: Regular physical activity helps stimulate bowel contractions (peristalsis), which is essential for regularity.

Conclusion: Balance is Key to Bowel Health

While a high-protein diet is popular for various fitness and weight management goals, its impact on your bowels is not a simple matter of cause and effect. It is the common practices associated with these diets, such as reducing fiber intake and becoming dehydrated, that are often to blame for constipation. Furthermore, individual sensitivities and the choice of protein source, whether animal- or plant-based, can influence your digestive comfort. By deliberately balancing your high-protein intake with plenty of fiber, proper hydration, and a diverse range of nutrients, you can reap the benefits of a protein-rich diet without compromising your digestive health. Focusing on whole, nutrient-dense foods and listening to your body's signals is the best way to maintain regularity and overall wellness. For further reading on the link between protein and constipation, you can consult this article from Healthline.

Frequently Asked Questions

Yes, protein powder can cause constipation, but it is not the protein itself that is the issue. The problem often lies in the lack of fiber and fluids accompanying protein shakes or bars, or the replacement of whole foods with supplements. Ensure your diet includes fiber-rich foods and plenty of water.

A high-protein, low-carb diet often causes constipation because it excludes many fibrous carbohydrates found in fruits, vegetables, and whole grains. Fiber is essential for adding bulk to stool and promoting regular bowel movements. Without it, stools become hard and difficult to pass.

To prevent constipation, increase your fiber intake with plenty of fruits, vegetables, and legumes, stay well-hydrated by drinking enough water, and engage in regular physical activity. Consider adding plant-based protein sources like lentils and chickpeas to your meals for extra fiber.

Diarrhea from protein shakes can be caused by lactose intolerance if the shake contains whey or casein, or by artificial sweeteners and sugar alcohols that have a laxative effect. Your body may also need time to adjust to a sudden increase in a specific protein or supplement.

High-protein diets with low fiber can alter the composition of the gut microbiome, potentially reducing beneficial bacteria and increasing those that produce toxic metabolites from undigested protein. Plant-based proteins, with their natural fiber content, can promote a healthier microbial balance.

Animal protein is generally highly digestible, but since it contains no fiber, it does not aid the digestive process in the same way plant protein does. Plant-based proteins are often rich in fiber and act as a prebiotic for gut bacteria, which is beneficial for overall digestive health.

Adults should aim for a daily fiber intake of 25-38 grams, depending on age and gender. This can be achieved by prioritizing fiber-rich foods like vegetables, fruits, whole grains, nuts, and seeds with every meal.