Social media users can actively choose how they portray themselves and review the information they share to form and manage positive impressions on their audience. A high Body Mass Index (BMI) can lead to a bias of attention towards self-reported unattractive personal body areas. This dysfunctional body-related attention can lead to increased body dissatisfaction. Concerning social networks, people who usually post more photos on Instagram more frequently show higher body satisfaction. The main objective of this work was to analyze the relationship between BMI in young people, their own exposition on Instagram, positive body image and certain psychological variables: self-esteem, coping and well-being. The population-based sample consisted of 687 young Instagram users aged between 18 to 35 years old. The results found in this work revealed that BMI had a significant influence on the body exposure on Instagram in both genders, as well as in body image and certain psychological variables, such as coping and well-being. Moreover, we found that there is not a direct relation between BMI and the exposure of the entire body on Instagram. This relationship exists through positive body image, appearance care and management appearance behaviors. These results imply that positive body image affects body’s exposure, so people with obesity or overweight tend to upload less photos with half or full body visible than people with normal weight or underweight. This is not because of their weight, but their valuation and appreciation of their bodies.