Tuna is a popular source of lean protein and omega-3 fatty acids, and is generally considered highly digestible. Despite its nutritional benefits, many people report experiencing digestive discomfort, particularly flatulence, after eating it. This gas production is a normal biological process. Intestinal gas occurs when unabsorbed substances reach the large intestine and interact with resident bacteria.
Why Tuna Digestion Can Cause Gas
Tuna, a concentrated protein source, contains high levels of sulfur-containing amino acids, primarily methionine and cysteine. While the body absorbs most of these, any undigested portion travels to the colon.
In the large intestine, gut microbes ferment these sulfur-rich compounds. This microbial activity produces various gases, including hydrogen sulfide (H2S). Hydrogen sulfide is a volatile sulfur compound known for its strong, unpleasant odor, which causes odorous flatulence after consuming tuna.
The preparation of tuna also influences gas production. While lean cuts are low in fat, oil-packed varieties or those prepared with mayonnaise add significant fat. High-fat foods slow down gastric emptying and digestion. This slower passage gives gut bacteria more time to ferment undigested protein, potentially increasing gas volume and discomfort.
The Role of Histamine and Individual Tolerance
A distinct source of digestive trouble is the accumulation of biogenic amines, notably histamine. Tuna is naturally high in the amino acid histidine. If the fish is not stored properly, bacteria convert histidine into histamine. Since this process depends on time and temperature, poorly handled tuna contains significantly higher histamine levels.
High histamine levels can cause scombroid poisoning, which mimics an allergic reaction with symptoms like diarrhea, cramps, and gas. Even without poisoning, some individuals struggle to process normal histamine levels due to a deficiency in the enzyme diamine oxidase (DAO). DAO is responsible for breaking down histamine in the digestive tract.
When the body’s DAO enzyme cannot keep pace with the ingested histamine, the excess amine is absorbed, causing systemic symptoms like bloating and gas. These symptoms are frequently mistaken for standard indigestion or a food allergy. For sensitive individuals, the issue is the acquired chemical compound resulting from the fish’s handling, not the fish protein itself.
Strategies for Reducing Digestive Discomfort
To mitigate histamine-related discomfort, ensure the tuna is as fresh as possible, since histamine levels increase rapidly with poor temperature control. If consuming canned tuna, draining the liquid helps remove residual oils or preservatives that might contribute to digestive upset.
To address gas from sulfur-containing amino acids, consume smaller portions of tuna. This presents a less overwhelming load for the digestive system and gut bacteria. Combining tuna with non-fermentable, low-gas side dishes, such as white rice or carrots and zucchini, can also assist in smoother digestion.
Eating slowly and chewing food thoroughly reduces swallowed air, minimizing one source of gas. For those with confirmed DAO deficiencies, consuming supplements containing the diamine oxidase enzyme before a meal may help the body break down histamine more efficiently.