In agreement to the Joint Programming Initiative “A Healthy Diet for a Healthy Life”, the transnational and multidisciplinary AMBROSIA project fits with the areas of food and health tackling one of major social challenges in current healthcare, the undernutrition in a well-defined “older” population, or rather Heart Failure (HF) and Atrial Fibrillation patients (AF). In this patients’cohort, undernutrition, is one key factors leading through inflammation, to loss of function, disability and, ultimately, to death. In addition, AF and HF synergistically contribute to determine a frail status. Undernourished AF and HF patients enter a vicious cycle “of undernutrition, inflammation, cachexia”, determining a progressive cognitive decline and lean body mass regression. .Since the inflammation is closely related with the health of intestinal microbiota, shaping the gut microbiota composition with a probiotic-based food, specifically enriched with key nutrients, could be an efficacious and safe approach to break this cycle improving the cognitive functioning and skeletal muscle mass. AMBROSIA is based on a novel research, it was planned to leverage and blend the skills of all applicants, so that there is a partnership to achieve the main objectives and an even distribution of tasks in the various work packages. AMBROSIA aims to develop an innovative food product to prevent undernutrition in HF and AF older patients: a new chocolate AMBROSIA bar containing specific mix of probiotic strains and a cocktail of micro/macronutrients (fibers, protein hydrolysates, coenzyme Q10); further studies on the metabolism and absorption of novel hydrolysates will be performed involving the patient association. In addition, the realization of a proper-realistic strategy from development and delivery of the AMBROSIA bar to the HF and AF patients is included. The efficacy of “AMBROSIA” bar on undernutrition prevention and its impact on cognitive functioning and skeletal muscle mass of older HF and AF patients will be evaluated through a prospective monocentric interventional clinical study. Finally, statistical and machine learning methods will be developed for the identification of features from the “Microbiota-Inflammation-Brain axis” that are predictive for undernutrition (biomarkers) and/or related to AMBROSIA bar treatment outcome.