Why Does Protein Give You Gas?
By: Nicholas Belden
Tags: Protein, Functional Medicine, Nutrition, Ibs, Gut Health

Gas Creation

No, not the product from Shell Oil that lets you drive around, but rather the gas and subsequent flatulence that our own body creates. Gas in the gut comes from four sources: 1) Swallowed air and air mixed with food, 2) Bacterial fermentation of food products, 3) Chemical reactions in the gut (food mixing with digestive juices), and 4) Diffusion of gases from the bloodstream (Levitt et al, 1970). For our purposes, we’re going to be referring to mostly numbers 2 & 3, as 75% of gas creation comes from bacterial fermentation (Hasler, 2006).

Once you have a buildup of gas, sometimes it just becomes too uncomfortable to handle, and you feel like you have to let it out. Fortunately, most of us have a pretty high tolerance of gas build-up before we start to experience abdominal pain or discomfort (Serra et al, 1998). The human body is also tremendous at clearing gas, evident in the previously cited study where researchers infused gas into healthy subjects (imagine that plane ride) in a dose-dependent manner, and saw a dose-dependent gas clearance (aka the people who had more gas infused in them excreted more gas out).

Gas commonly occurs after a meal, as solid and liquid ingestion accelerate the passage of gas through the digestive tract. The major gases in flatus (fancy medical term for farts) are Hydrogen, Methane, Oxygen, Carbon Dioxide and Nitrogen. Hydrogen Sulfide is a less commonly produced gas, but when it is you and everyone around you sure knows about it (Hydrogen Sulfide produces that classic ‘rotten egg’ smell).

Protein Digestion

Some people see gas after a high protein meal as a signal that the protein was not digested well… sort of. Protein consists of peptides and amino acids bonded together (amino acids are the building blocks for protein). Once you’ve had protein and it reaches the stomach, Hydrochloric Acid (HCl) is released, which ‘turns on’ an enzyme called Pepsin to start breaking down the protein. Once that partially digested protein reaches the small intestine (SI), the pancreas secretes more enzymes to further break down the protein into single amino acids, or several amino acids still bonded together (Tri- and Dipeptides). From this point the amino acids should be absorbed in the small intestine.

Sometimes, for reasons we will discuss shortly, undigested protein is not absorbed in the SI and makes its way to the large Intestine (LI). From there, the ‘protein remnants’ can be fermented by our gut bacteria. Gut bacteria, particularly in the LI, normally ferment carbohydrates (dietary fiber and resistant starches) as fuel. When our gut bacteria start to ferment protein rather than carbohydrates, some questionable compounds are made: ammonia, phenols, amines, and the previously mentioned Hydrogen Sulfide gas (Yao et al, 2016).

That is one of my concerns over the new craze of the carnivore diet, as we don’t have any long term data on the effects of really high protein consumption (greater than 50% of calories) on the gut microbiome. Quick side note, I’ve done a carnivore diet, and it can be done right with proper attention to consuming organ meats, a collagen source, and a quality fat source.