Why do protein shakes make me poop?

Why do protein shakes make me poop?


Protein shakes have become increasingly popular among fitness enthusiasts and athletes as a convenient and effective way to supplement their protein intake. However, some individuals may experience an unexpected side effect after consuming protein shakes – an increased frequency of bowel movements or even diarrhea. This article aims to explore the reasons behind why protein shakes can make some people poop more frequently.

Protein Content and Digestion

Protein Content: Protein shakes are typically high in protein, which is an essential macronutrient for muscle growth, repair, and overall health. The protein content in these shakes can vary depending on the brand and type of protein used, such as whey, casein, soy, or plant-based proteins.

Digestion Process: When we consume protein, our body breaks it down into amino acids through the process of digestion. This breakdown primarily occurs in the stomach and small intestine, where enzymes help break down the protein molecules into smaller components for absorption.

Lactose Intolerance and Dairy-Based Protein Shakes

Lactose Intolerance: Many protein shakes, especially those made from whey or casein protein, are derived from dairy sources. Lactose, a sugar found in milk and dairy products, can be difficult for some individuals to digest due to lactose intolerance. Lactose intolerance occurs when the body lacks the enzyme lactase, which is responsible for breaking down lactose.

Diarrhea and Lactose Intolerance: In individuals with lactose intolerance, consuming dairy-based protein shakes can lead to gastrointestinal symptoms, including diarrhea. This happens because undigested lactose moves into the large intestine, where it ferments and draws water into the colon, resulting in loose stools or diarrhea.

Artificial Sweeteners and Sugar Alcohols

Artificial Sweeteners: Protein shakes often contain artificial sweeteners like sucralose, aspartame, or acesulfame potassium to enhance the taste without adding extra calories. While these sweeteners are generally recognized as safe by regulatory authorities, some individuals may experience gastrointestinal discomfort or laxative effects when consuming them.

Sugar Alcohols: Another common ingredient found in protein shakes is sugar alcohols, such as xylitol, sorbitol, or erythritol. These sugar substitutes are lower in calories and have a minimal impact on blood sugar levels. However, excessive consumption of sugar alcohols can have a laxative effect and lead to diarrhea.

Inadequate Fiber Intake

Fiber Content: Protein shakes often lack dietary fiber, which is an essential nutrient for maintaining healthy bowel movements. Fiber adds bulk to the stool and helps regulate bowel movements by promoting regularity.

Insufficient Fiber: If protein shakes are consumed as a meal replacement or a significant portion of one’s diet, it may result in inadequate fiber intake. This lack of fiber can lead to constipation or irregular bowel movements. However, some individuals may experience the opposite effect, with increased bowel movements, as the body tries to compensate for the low fiber content.


While protein shakes are generally considered safe and beneficial for most individuals, some people may experience an increase in bowel movements or even diarrhea after consuming them. This can be attributed to factors such as lactose intolerance, artificial sweeteners or sugar alcohols, and inadequate fiber intake. It is important to listen to your body and make adjustments to your protein shake routine if you experience any gastrointestinal discomfort. Consulting a healthcare professional or registered dietitian can also provide personalized guidance and recommendations.


– Mayo Clinic. (2021). Lactose intolerance. Retrieved from mayoclinic.org/health/lactose-intolerance
– National Institute of Diabetes and Digestive and Kidney Diseases. (2020). Lactose Intolerance. Retrieved from niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance
– National Institute of Diabetes and Digestive and Kidney Diseases. (2020). Gas in the Digestive Tract. Retrieved from niddk.nih.gov/health-information/digestive-diseases/gas-digestive-tract
– National Institute of Diabetes and Digestive and Kidney Diseases. (2020). Eating, Diet, & Nutrition for Irritable Bowel Syndrome. Retrieved from niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/eating-diet-nutrition
– Harvard Health Publishing. (2021). Protein: Are You Getting Enough? Retrieved from health.harvard.edu/blog/protein-how-much-do-you-need-201506188096