Knowledge BaseYou're Questions Answered


Can casein protein powder cause diarrhea?

Casein protein powder can cause diarrhea in some individuals, especially those who are sensitive to dairy products or lactose-intolerant. Casein, a major protein found in milk, digests slowly, which can sometimes lead to gastrointestinal issues, including diarrhea, in susceptible individuals1.

There are several reasons why casein protein powder might lead to diarrhea:

  • Lactose Content: Some casein protein powders contain lactose, which can cause diarrhea in lactose-intolerant individuals. The inability to properly digest lactose leads to its fermentation in the colon, resulting in gas, bloating, and diarrhea2.
  • Dairy Sensitivities: Aside from lactose intolerance, some people have a sensitivity to dairy proteins like casein, which can trigger an inflammatory response in the gut, leading to diarrhea3.
  • High Protein Intake: Consuming high amounts of protein, particularly in supplement form, can sometimes overwhelm the digestive system, particularly if dietary fiber intake is not sufficient to help manage digestion4.

To mitigate the risk of diarrhea when using casein protein powder, consider the following tips:

  • Choose casein protein powders that are low in lactose or lactose-free, especially if you are lactose intolerant.
  • Increase your intake of dietary fiber to help support digestive health and prevent constipation, which can sometimes accompany the use of protein supplements.
  • Introduce casein protein slowly into your diet to allow your digestive system to adjust.
  • Stay hydrated by drinking adequate amounts of water, as dehydration can contribute to digestive problems.

If diarrhea persists despite taking these measures, it may be advisable to consult with a healthcare provider to rule out other underlying causes or to consider an alternative protein supplement5.


  1. Boirie, Y., Dangin, M., Gachon, P., Vasson, M. P., Maubois, J. L., & Beaufrère, B. (1997). Slow and fast dietary proteins differently modulate postprandial protein accretion. Proceedings of the National Academy of Sciences, 94(26), 14930-14935.
  2. Suarez, F. L., Savaiano, D., & Levitt, M. D. (1995). A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance. New England Journal of Medicine, 333(1), 1-4.
  3. Høst, A. (1994). Cow's milk protein allergy and intolerance in infancy. Some clinical, epidemiological and immunological aspects. Pediatric Allergy and Immunology, 5(5 Suppl), 1-36.
  4. Slavin, J. (2005). Dietary fiber and body weight. Nutrition, 21(3), 411-418.
  5. Skovbjerg, H., Norén, O., Anthony, P., Sjöström, H., & Flensburg, J. (1981). Further characterization of intestinal lactase/phlorizin hydrolase. Biochimica et Biophysica Acta (BBA) - Enzymology, 659(2), 302-311.
The content on this site has not been written, reviewed or endorsed by a medical professional. We assume no liability for the misuse of supplements and recommend you review the label of any product, as well as consulting with your health care professional.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.