Social networks become a global communication phenomenon. The paper describes the term "fitness" and discusses the advantages and disadvantages of using social networks. The main goal was to show the impact they have on the fitness industry. In the Republic of Croatia, Facebook and Instagram are the most widely used, which is the main reason why those have been subjects of the study. It has been shown that social networks are an excellent channel for promoting a healthy lifestyle because the preferred audience is using them. Apart from reading literature, this is also proven by the personal experience of prominent fitness trainers who have relayed their communication to social networks. They can interact with fans and highlight the importance of regular physical activity and healthy eating on Facebook and Instagram. Of course, social networks are also used for self-promotion and sale of their Nutrition and Training Plans. In fact, fitness trainers become, thanks to their own popularity, educators of healthy living. They are trying to fight against prejudice, "fast" diets and self-employed experts who usually give false promises about fast weight loss. Fitness trainers believe that the greatest advantages of communication through Facebook and Instagram are the freedom of speech and two-way communication with their fans. Also, their opinions can reach a large number of people in a short time. New functionalities on social networks are bringing new ways for promotion - those are the reasons why more and more content related to the fitness industry is emerging every day. All this is happening with the aim of making users choose regular physical activity, balanced and healthy nutrition, and to become ultimately "fit".