What happens to poop on a high-protein diet? Everything you need to know

January 7, 2026 •

3 min read

According to the National Institute of Diabetes and Digestive and Kidney Diseases, constipation is a common complaint, and dietary changes are often a contributing factor. Understanding what happens to poop on a high-protein diet is the first step toward managing digestive issues and maintaining a healthy gut while pursuing your fitness goals.

Quick Summary

A high-protein eating plan can significantly alter bowel movements, potentially causing constipation due to low fiber and dehydration, or diarrhea from specific supplements. Diets heavy in animal protein can also change the gut microbiome, sometimes causing digestive issues and unpleasant odor.

Key Points

Constipation Risk: Constipation is a common side effect of high-protein diets due to often low fiber and water intake, not the protein itself.
Hydration is Key: Increased protein metabolism requires more water to process waste; insufficient fluid intake leads to harder, drier stools.
Diarrhea Triggers: Diarrhea can result from artificial sweeteners or lactose in certain protein supplements, causing osmotic effects in the colon.
Gut Microbiome Changes: A diet high in animal protein and low in plant fiber can negatively alter the gut microbiome, potentially increasing inflammatory bacteria.
Pungent Stool Odor: A higher intake of protein, especially from animal sources, can lead to more sulfur-containing compounds produced during fermentation, causing foul-smelling poop.
Balance is Best: The most effective solution is a balanced diet that includes high-protein foods alongside plenty of fiber from fruits, vegetables, and whole grains.

Common Causes for Altered Bowel Movements

When you increase your protein intake, especially if it's accompanied by a reduction in carbohydrates and fiber, your digestive system can react in a few predictable ways. The primary driver behind many digestive issues is not the protein itself, but rather the nutritional imbalance created by focusing on one macronutrient.

The Low-Fiber Trap

Many popular high-protein diets emphasize animal products like meat, fish, and eggs, which contain no dietary fiber. Fiber is essential for digestive health because it adds bulk to stool, helping it move smoothly through the intestines. When fiber is sidelined in favor of protein, transit time slows, leading to hard, dry stool that is difficult to pass, resulting in constipation. This is especially common for those who swap out whole grains, fruits, and vegetables for extra meat or protein shakes.

The Dehydration Effect

Protein metabolism increases the body's need for fluids to help flush out waste products, like urea, via the kidneys. If you don't increase your water intake to match your higher protein consumption, your colon will absorb more water from your waste to compensate, making your stool even drier and harder. This cycle exacerbates constipation and can cause significant discomfort.

Constipation vs. Diarrhea

While constipation is the most frequently reported issue, some individuals experience the opposite—diarrhea. The culprit is often hidden within the convenience of protein supplements:

Artificial Sweeteners and Sugar Alcohols: Common in many protein powders and bars, these can cause a laxative effect in some people. Sugar alcohols are not fully absorbed by the body and can draw water into the colon, leading to loose stools.
Lactose Intolerance: Whey and casein protein powders are derived from milk and contain lactose. If you are lactose intolerant, consuming these products can cause gas, bloating, and diarrhea.

The Role of the Gut Microbiome

Your gut is home to trillions of bacteria that play a critical role in digestion and overall health. The balance of this microbial community, or microbiome, can be heavily influenced by your diet.

Animal vs. Plant Protein and Gut Health


Feature	High Animal Protein Diet	High Plant-Based Protein Diet
Fiber Content	Lacks fiber	High in fiber
Microbial Diversity	Can reduce diversity, decreasing beneficial bacteria like Roseburia	Supports a more diverse and healthy microbiome
Fermentation Byproducts	Associated with harmful byproducts like ammonia and hydrogen sulfide	Promotes beneficial short-chain fatty acids (SCFAs)
Risk of Constipation	Higher risk due to low fiber	Lower risk due to high fiber
Stool Odor	Often more pungent due to bacterial fermentation	Generally less pungent due to healthier gut environment

A diet high in animal protein and low in plant-based fiber can shift the gut's bacterial composition, potentially increasing harmful metabolites. This can lead to increased gas, odor, and inflammation. Plant-based proteins, on the other hand, often contain fiber which supports a balanced gut ecosystem.

Practical Solutions for Digestive Comfort

Digestive issues on a high-protein diet can be managed by focusing on restoring digestive balance.

Increase Your Fiber Intake

Include Fibrous Vegetables: Incorporate leafy greens and other vegetables like broccoli.
Choose Whole Grains and Legumes: Opt for whole grains, lentils, and beans.
Snack on High-Fiber Options: Choose snacks like almonds or berries.

Prioritize Hydration

Drink More Water: Aim for 2 to 3 liters daily to aid waste removal.
Start Your Day with Fluids: Drink water in the morning to stimulate digestion.
Monitor Urine Color: Pale urine indicates sufficient hydration.

Consider Probiotics and Enzymes

Eat Fermented Foods: Include foods like yogurt and kefir.
Consider Supplements: Probiotic or digestive enzyme supplements may help with persistent issues.

Diversify Your Protein Sources

Include plant-based options like tofu and lentils to provide fiber and support a diverse gut microbiota.

Conclusion

High-protein diets can cause digestive side effects like constipation, diarrhea, and odor changes. These are often due to insufficient fiber and hydration. Balancing protein intake with fiber-rich foods and adequate water can help mitigate these issues. Consulting a dietitian is recommended for personalized guidance.

Practical Steps for Better Digestion

Increase Fiber Gradually: Avoid sudden increases in fiber.
Stay Active: Regular exercise promotes bowel movements.
Chew Your Food Thoroughly: Proper chewing aids digestion.
Avoid Excess Protein Supplements: If experiencing diarrhea, evaluate supplement ingredients.
Listen to Your Body: Adjust your diet based on your body's reactions.

Frequently Asked Questions

A higher intake of protein can increase the production of sulfur-containing compounds during bacterial fermentation in the colon, which can lead to a more pungent stool odor.

Yes. Protein shakes can cause constipation if they lead to lower fiber intake, or cause diarrhea if they contain artificial sweeteners or if you have lactose intolerance from whey protein.

To prevent constipation, increase your intake of dietary fiber from sources like vegetables, fruits, and legumes, and ensure you drink plenty of water throughout the day.

Yes, animal proteins lack fiber and can alter the gut microbiome, while plant-based proteins come with fiber that helps regulate bowel movements and supports beneficial gut bacteria.

Proper hydration is crucial as the body needs more water to process and eliminate waste products from increased protein metabolism. Insufficient water can lead to dehydration and harder, more difficult-to-pass stools.

Yes, probiotics can help by restoring and maintaining a healthy balance of gut bacteria, which supports regular bowel movements and can reduce digestive discomfort.

If you experience persistent digestive problems, it's advisable to adjust your diet by balancing your macronutrient intake, or consult a healthcare professional to rule out underlying issues.