STEARIC ACID (18:0) IS A SATURATED FATTY ACID FOUND IN FOODS SUCH AS COCOA BUTTER, MEAT AND DAIRY. UNLIKE OTHERDIETARY SATURATED FATS WHICH ARE CONSIDERED TO BE UNHEALTHY, STEARIC ACID HAS A NEUTRAL EFFECT ON BLOOD LDL CHOLESTEROL LEVELS AND HAS BEEN INVERSELY ASSOCIATED WITH CARDIOVASCULAR DISEASE (CVD) RISK. EXISTING STUDIES HAVE EXPLORED POSSIBLE MECHANISMS SUCH AS REDUCED INTESTINAL ABSORPTION, INCREASED EXCRETION OR OXIDATION, AND CONVERSION TO OLEIC ACID IN THE BODY, BUT THESE DO NOT FULLY ACCOUNT FOR ITS DISTINCT METABOLIC EFFECTS. PRELIMINARY DATA INDICATE THAT STEARIC ACID MAY INFLUENCE THE GUT MICROBIOME, PARTICULARLY MICROBES INVOLVED IN BILE ACID (BA) METABOLISM. CHANGES IN THESE MICROBES CAN ALTER THE PRODUCTION OF SECONDARY BILE ACIDS, WHICH ARE KNOWN TO PLAY ROLES IN LIPID METABOLISM AND INFLAMMATION. MOST PREVIOUS RESEARCH HAS RELIED ON STOOL SAMPLES TO STUDY THE GUT MICROBIOME. HOWEVER, STOOL REFLECTS MICROBIAL ACTIVITY PRIMARILY IN THE LARGE INTESTINE (COLON), NOT THE ENTIRE GASTROINTESTINAL (GI) TRACT. MICROBIAL TRANSFORMATION AND REABSORPTION OF BAS OCCUR MAINLY IN THE ILEUM, A REGION OF THE SMALL INTESTINE, WHICH IS NOT WELL-REPRESENTED IN STOOL-BASED ANALYSES. TO ADDRESS THIS LIMITATION, WE WILL CONDUCT A CLINICAL TRIAL IN OLDER ADULTS USING AN INGESTIBLE SAMPLING DEVICE (MINI-PILL) TO COLLECT REGION-SPECIFIC GASTROINTESTINAL SAMPLES AND EVALUATE THE EFFECTS OF DIETARY STEARIC ACID ON GUT MICROBIAL COMPOSITION, FUNCTION, AND BA METABOLISM. FINDINGS FROM THIS WORK WILL PROVIDE A MORE DETAILED UNDERSTANDING OF THE EFFECTS OF STEARIC ACID WITHIN THE GUT AND ITS RELATIONSHIP TO HOST METABOLIC PROCESSES RELEVANT TO CARDIOVASCULAR HEALTH. THIS WILL CONTRIBUTETO THE EVIDENCE BASE NEEDED TO MODIFY CURRENT DIETARY GUIDANCE/NUTRIENT LABELING RELATED TO SATURATED FAT, AND THE POTENTIAL USE OF STEARIC ACIDAS AN ALTERNATIVE FOR TRANS FATTY ACIDS (TFAS) IN THE FOOD SUPPLY.