Trans fats can be produced by GI bacteria, a process common in ruminants. These trans fats can yield beneficial compounds such as CLA and may not have the adverse effects that commercially produced trans fats from processed foods may have.
Dietary triglycerides are broken down into free fatty acids and monoglycerols by pancreatic lipase and then absorbed in the small intestine. However, the efficiency of absorption is reduced without adequate pancreatic lipase or bile acids, and unabsorbed fatty acids can make their way into the large intestine. Here, unsaturated fatty acids can undergo “biohydrogenation” by anaerobic bacteria. This process takes place in the stomach of ruminant animals such as cattle and sheep. Early in vitro studies suggest that “biohydrogenation” of polyunsaturated fatty acids can take place in humans and produces various forms of cis- and trans-fatty acids (Howard 1999).
In nature, most unsaturated fatty acids (containing at least one double bond) are in the “cis” position except for the trans fatty acids produced by bacterial biohydrogenation in ruminant animals. These trans fats appear to be different from those produced commercially through partial hydrogenation. In 2015 the FDA removed dietary trans fats from the generally recognized as safe (GRAS) list, and in 2018 banned partially hydrogenated oils/trans fats due to their association with increased cardiovascular risk (Gropper 2021).
The most abundant trans fatty acid produced in ruminant animals is trans-11 C18:1 which is further metabolized to stearic acid or conjugated linoleic acid (CLA). Research indicates that CLA, found in the milk and meat of ruminant animals, has antioxidant and anticarcinogenic effects despite it being a trans fat metabolite. Human studies suggest that CLA may have anti-obesity effects as well (Mosley 2002). Several lactic acid bacteria appear to work in conjunction to produce CLA, including L plantarum, L. casei, and L rhamnosus (Kishino 2013), as well as Roseburia species (Hoyles 2010).
The principal commercially produced trans fat is elaidic acid (trans 18:1, n-9), a compound associated not only with CVD but with systemic inflammation, accumulation of cholesterol in macrophages, and promotion of atherosclerotic plaque (Lottenberg 2018).
Animal studies demonstrate that industrially produced trans fats promote dysbiosis, decreasing most beneficial bacteria and increasing potentially harmful bacteria (Ge 2019). Compared to saturated fat, consumption of industrial trans fats was also associated with intestinal inflammation, impaired glucose tolerance, and exacerbation of metabolic disease (Okamura 2021).
In conclusion, industrial trans fats used in processed foods are associated with adverse health effects and have been banned by the FDA.
The trans fats produced by bacterial biohydrogenation in ruminant animals can be converted to less harmful and potentially beneficial compounds, including CLA, which can be found in the meat and milk of these animals.
Although the extent and effects of biohydrogenation in human health require more research, it would be prudent to provide digestive support with lipase and bile acids and identify and correct dysbiosis.
References
Gropper, Sareen S.; Smith, Jack L.; Carr, Timothy P. Advanced Nutrition and Human Metabolism. 8th edition. Wadsworth Publishing Co Inc. 2021.
Howard, F A, and C Henderson. “Hydrogenation of polyunsaturated fatty acids by human colonic bacteria.” Letters in applied microbiology vol. 29,3 (1999): 193-6. doi:10.1046/j.1365-2672.1999.00616.x
Hoyles, Lesley, and J. Wallace R. "Gastrointestinal tract: intestinal fatty acid metabolism and implications for health." Springer, 2010. 3119-3132.
Ge, Yueting et al. “Effect of industrial trans-fatty acids-enriched diet on gut microbiota of C57BL/6 mice.” European journal of nutrition vol. 58,7 (2019): 2625-2638. doi:10.1007/s00394-018-1810-2
Kishino, Shigenobu et al. “Polyunsaturated fatty acid saturation by gut lactic acid bacteria affecting host lipid composition.” Proceedings of the National Academy of Sciences of the United States of America vol. 110,44 (2013): 17808-13. doi:10.1073/pnas.1312937110
Lottenberg, Ana Maria, et al. "Influence of Diet on Endothelial Dysfunction." Endothelium and Cardiovascular Diseases. Academic Press, 2018. 341-362.
Mosley, Erin E et al. “Microbial biohydrogenation of oleic acid to trans isomers in vitro.” Journal of lipid research vol. 43,2 (2002): 290-6.
Okamura, Takuro et al. “Trans Fatty Acid Intake Induces Intestinal Inflammation and Impaired Glucose Tolerance.” Frontiers in immunology vol. 12 669672. 29 Apr. 2021, doi:10.3389/fimmu.2021.669672
Ghosh, Asit Ranjan. "Probiotics in the Rescue of Gut Inflammation." Therapeutic, Probiotic, and Unconventional Foods. Academic Press, 2018. 101-116.