Actor Im Siwan went to extreme lengths for his role in the movie '1947 Boston', lowering his body fat percentage to roughly 6% through strict self-management and a rigorous diet. This shocking revelation came during a talk released on the 'Vivo TV' channel, featuring Siwan and his co-star Ha Jung Woo, alongside broadcaster Song Eun Yi.

Siwan adopted this strict regimen due to his role as a marathoner in '1947 Boston'. When a shocked Song Eun Yi asked how one could achieve such a low body fat percentage, Si-wan jokingly quipped, "You almost have to give up being human. Regular exercise is a given, but I had to eat chicken breast until I got fed up with it." He soberly noted the impact this routine had on his life, stating, “Eating is one of life's joys, but that joy was greatly diminished,” plainly expressing the severity of the sacrifices he had made for his role.

Maintaining the habit of health consciousness, Siwan revealed that he continues to run marathons even after the film’s completion. "Running suits my personality well. I decided to continue with marathons after shooting wrapped," Siwan shared, mentioning that he completed a 10 km run alone before receiving a call from seasoned runner, Sean. He extended an invitation to join his running group, an offer that led to the actor joining regular group runs. Siwan confessed, "Reaching your limit and pushing past it is where you find the allure of a marathon. Before you know it, you cross the finish line." It appears that while the actor indeed sacrificed a lot for his role, he also gained a lasting passion for fitness and running marathons.