His research focuses on physical activity and clinical epidemiology to study the impact of physical activity on energy metabolism and the development of cardiovascular diseases, particularly obesity and insulin resistance. Moreover, his research has unequivocally shown that regular physical activity has an important protective effect on cardiovascular health already in youth. Dr. Ruiz got the Prestigious Ramón y Cajal Research Fellow becoming the first Ramón y Cajal researcher with a Sport Science background in Spain, and his project was the best project application out of 6 given in the area of Clinical Medicine and Epidemiology. He has been the PhD supervisor of researchers who got prestigious postdoctoral contracts such as Ramón y Cajal, Marie Curie, Talent Hub, Juan de la Cierva, Ramón Areces or Martín Escudero. Jonatan is honorific member of the Spanish Young Academy.