The Heartbreak Of Protein Farts

The Heartbreak Of Protein Farts

Published on Tuesday, March 07, 2023 by Alexander Koch

Protein is one of the three macronutrients needed for survival.  

Protein plays an essential role in metabolism, providing amino acids, the building blocks for many of our body’s structures, including skeletal muscle. The USDA recommends a daily protein intake of 0.8g/kg of body mass for the average person and recommended daily protein requirements climb higher than that, depending on who you are.  

For example, elderly folks have a reduced ability to use ingested proteins, so it is recommended that they consume a higher (≥1.0g/kg) amount to preserve muscle mass and reduce their chances of functional disability

Athletes have higher protein requirements as well. To optimize muscle repair and add extra muscle mass, recommended protein ingestion may rise to as high as 2.0g/kg, over double the recommendation compared to sedentary folks.

Protein Can Rock Your Intestines

With all the good protein does for your body, it is hard to complain… But.  

High protein intakes, particularly from protein supplements, are often associated with an increase in flatulence. Particularly smelly flatulence.

Where does intestinal gas come from? Intestinal gas comes from the fermentation of undigested carbohydrates. 

Proteins aren’t carbohydrates, so how does high protein intake relate to more intestinal gas? 

Well, there are two main reasons: Firstly, if you mindfully consume a lot of protein, especially adding more protein through meal supplements, such as shakes and bars, you run the risk of displacing other essential nutrients, particularly fiber. Lack of dietary fiber leads to constipation, which leads to undigested carbohydrates spending an extended period fermenting in your colon and producing higher quantities of gas. 

Secondly, protein supplements are often flavored with low-digestible carbohydrates. Two things make food taste good – fat and sugar. To create a low-fat, low-carbohydrate protein supplement, manufacturers will blend the protein with something to make it taste sweeter. Many protein supplements are milk-based, and lactose, the sugar in milk, can be present in high quantities. Lactose is notoriously hard to digest for adults, thus it has the potential to create intestinal gas. In addition to lactose, food manufacturers often add sugar alcohols to their protein items. Sugar alcohols are low-digestible carbohydrates that enhance flavor without adding calories but have an unfortunate habit of exacerbating GI symptoms.

And that smell? A lot of that can be traced to a specific amino acid, L-tryptophan. When digested, L-tryptophan is easily converted to a structurally similar aromatic ring compound called skatole. This chemical is literally what gives feces its smell. Why that particular fact is my most vivid memory of the organic chemistry class I took in 1992 is a question I will never be able to answer…

Strategies For Coping

So how can one get their protein and still be suitable for polite company?  

1) Make sure you are consuming adequate fiber to keep your intestines flowing smoothly. Protein is an essential part of a good mixed diet, but fiber sources such as vegetables, fruits, and grains should not be discarded.  

2) Check your protein sources for the presence of lactose or sugar alcohols – sorbitol, erythritol, xylitol, and maltitol are common sugar alcohols you can spot on a label. As an alternative, some protein brands are flavored with stevia. Stevia is a natural sweetener that may be beneficial to the gut microbiome and less likely to provoke gut irritation. 

  1. Claus, R., & Raab, S. (1999). Influences on skatole formation from tryptophan in the pig colon. Advances in experimental medicine and biology, 467, 679–684. 
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  4. Kasti, A. N., Nikolaki, M. D., Synodinou, K. D., Katsas, K. N., Petsis, K., Lambrinou, S., Pyrousis, I. A., & Triantafyllou, K. (2022). The Effects of Stevia Consumption on Gut Bacteria: Friend or Foe?. Microorganisms, 10(4), 744. 
  5. McGrath, R., Stastny, S., Casperson, S., Jahns, L., Roemmich, J., & Hackney, K. J. (2020). Daily Protein Intake and Distribution of Daily Protein Consumed Decreases Odds for Functional Disability in Older Americans. Journal of aging and health, 32(9), 1075–1083. 

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