Fecal Fat - Long Chain Fatty Acids Test

Long chain fatty acids (LCFAs) are fat molecules made of 12 or more carbon atoms. They form the majority of dietary fats found in foods like meat, dairy, nuts, and oils. During normal digestion, these fats are broken down and absorbed in the small intestine. Measuring LCFAs in stool offers a window into how efficiently this process is happening, and how well your gut, pancreas, and liver are working together to handle fat.

In healthy digestion, only small traces of LCFAs appear in feces because most dietary fat is broken down into smaller molecules, absorbed through the intestinal lining, and transported into the bloodstream. When LCFA levels in stool rise, it usually means fat digestion or absorption is impaired. This can occur in conditions such as exocrine pancreatic insufficiency (when the pancreas does not release enough enzymes to digest fat), celiac disease, or short bowel syndrome. In cystic fibrosis, for example, even with enzyme replacement therapy, long-chain fats are poorly absorbed, which can lead to essential fatty acid deficiency, a state that affects skin, brain, and cell membrane health.

Beyond digestion, fecal LCFAs are emerging as noninvasive markers of metabolic and intestinal health. Studies have shown that people with obesity tend to have higher levels of certain polyunsaturated long-chain fats (especially omega-3 and omega-6 types) in their stool. This may reflect differences in gut microbial metabolism or inefficiencies in fat processing. In men with colorectal cancer, elevated stool levels of n-6 fats like linoleic acid have been reported, suggesting these LCFA patterns might someday serve as early screening biomarkers for intestinal disease.