MICRONUTRIENT MALNUTRITION REMAINS A MAJOR PUBLIC HEALTH PROBLEM, AFFECTING MORE THAN 2 BILLION PEOPLE, BOTH DOMESTICALLY AND INTERNATIONALLY. IN PARTICULAR, WOMEN OF REPRODUCTIVE AGE ARE AT A HIGH RISK FOR MICRONUTRIENT DEFICIENCIES AND ANEMIA. FORTIFICATION OF FOODS WITH FOLIC ACID AND OTHER MICRONUTRIENTS IS AN EFFICACIOUS AND COST-EFFECTIVE PUBLIC HEALTH INTERVENTION TO ADDRESS MICRONUTRIENT DEFICIENCIES, AND HAS BEEN IMPLEMENTED IN OVER 85 COUNTRIES. THE IMPACT OF MICRONUTRIENT-FORTIFIED FOODS ON OTHER HEALTH OUTCOMES BEYOND MICRONUTRIENT DEFICIENCIES IS NEEDED TO FURTHER INFORM FORTIFICATION POLICIES AND GUIDELINES IN THE UNITED STATES AND GLOBALLY - AS ANY ADDITIONAL HEALTH BENEFITS FROM A PUBLIC HEALTH INTERVENTION COULD HAVE A SUBSTANTIAL IMPACT ON POPULATION HEALTH.DIETARY INTAKE OF KEY MICRONUTRIENTS PROVIDES SUBSTRATES THAT CAN BE USED BY THE GUT MICROBIOTA, COMPRISED OF BACTERIA, FUNGI, AND VIRUSES. NOT ONLY CAN THESE DIETARY SUBSTRATES MODIFY THE COMPOSITION OF MICROORGANISMS RESIDING IN THE HUMAN GUT, BUT THEY CAN ALSO INFLUENCE THEIR METABOLIC FUNCTION. PREVIOUS STUDIES HAVE EXPLORED THE IMPACT OF DIETARY INTERVENTIONS ON THE GUT MICROBIOME AMONG ADULTS IN HIGHER INCOME SETTINGS. HOWEVER, NO STUDIES TO DATE HAVE FOCUSED ON THE IMPACT OF CONSUMING MICRONUTRIENT-FORTIFIED FOODS AND NUTRITIONAL STATUS ON THE GUT MICROBIAL COMPOSITION, DIVERSITY, AND FUNCTION, AMONG WOMEN OF REPRODUCTIVE AGE.OUR RANDOMIZED CONTROLLED TRIAL AMONG 1,000 WOMEN OF REPRODUCTIVE AGE IN SOUTH INDIA, FUNDED BY THE CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC), REPRESENTS AN IDEAL OPPORTUNITY TO EVALUATE THE IMPACT OF MULTIPLE MICRONUTRIENT-FORTIFIED SALT ON THE GUT MICROBIOME (ESTIMATED DATE OF COMPLETION: MARCH 2023). THIS RANDOMIZED TRIAL WILL EXAMINE THE EFFICACY OF QUADRUPLE FORTIFIED SALT (QFS; IRON, IODINE, VITAMIN B12, FOLIC ACID, AND IODINE), COMPARED TO DOUBLE-FORTIFIED SALT (DFS; IRON, IODINE), USING A 2X2 FACTORIAL DESIGN, ON ANEMIA AND MICRONUTRIENT STATUS AMONG WOMEN OF REPRODUCTIVE AGE OVER A 12-MONTH PERIOD. WE PROPOSE TO ADD AN ASSESSMENT OF THE GUT MICROBIOME TO THE PARENT TRIAL DESIGN, WHICH IS A COST-EFFICIENT APPROACH TO ANSWER THE QUESTION: "DOES MULTIPLE MICRONUTRIENT-FORTIFIED SALT-- WITH IRON, IODINE, FOLIC ACID, AND VITAMIN B12--IMPACT THE COMPOSITION, DIVERSITY, AND FUNCTION OF THE GUT MICROBIOME OVER 12 MONTHS OF AD LIBITUM CONSUMPTION?'. WE AIM TO INCREASE OUR UNDERSTANDING OF THE LINKS BETWEEN AGRICULTURAL, NUTRITIONAL, AND DIETARY INPUTS AND THE GUT MICROBIOME IN WOMEN OF REPRODUCTIVE AGE (PRECONCEPTION) AND HELP IDENTIFY CRITICAL WINDOWS FOR INTERVENTION TO IMPROVE WOMEN'S HEALTH IN THE UNITED STATES AND GLOBALLY. WE HYPOTHESIZE THAT THE MULTIPLE MICRONUTRIENT-FORTIFIED INTERVENTION IN THIS TRIAL WILL IMPROVE THE COMPOSITION AND FUNCTION OF THE GUT MICROBIOME IN WOMEN OF REPRODUCTIVE AGE.THIS PROPOSAL, IN RESPONSE TO THE PRIORITY OF "FOOD SAFETY, NUTRITION, AND HEALTH", WILL ADDRESS THE CHALLENGES OF A GROWING DIVERSE POPULATION AND PERSISTING MICRONUTRIENT DEFICIENCIES USING FORTIFIED FOODS. THIS REPRESENTS A SUSTAINABLE SOLUTION FOR IMPROVING MICRONUTRIENT STATUS, INCLUDING HUMAN FOOD AND MICRONUTRIENT NEEDS. IN TERMS OF SUSTAINABILITY, FORTIFIED FOOD CAN BE PRODUCED BY LOCAL PRODUCERS, SUSTAINING THE ECONOMIC VIABILITY OF INDUSTRY OPERATIONS. FURTHER, FORTIFICATION IS COST-EFFECTIVE AND FORTIFIED FOODS SUCH AS SALT ARE AFFORDABLE, WIDELY CONSUMED, AND CAN BE INCORPORATED INTO EXISTING PRODUCTION AND DISTRIBUTION SYSTEMS.