Objectives: Two historical evidence supported the concept of Gamrosu. The first one was Jeho-tang, a selected thirst quencher in Chosun Dynasty and the second one was Saeng- Maek-san, Dongeuibogam`s recommendation as one of the qi-vigorating summer beverages. Gamrosu is a modified fasting therapy beverage which is manufactured from those two prescriptions and the carbohydrates (420.6 kcal/d). A retrospective observational study was conducted to evaluate the clinical outcomes. Methods: Thirty-three cases were reviewed at three local Korean Medical clinics that each site`s participant has finished the modified fasting for 10 consecutive days. Clinical outcomes were reviewed at pre- and post-fasting sessions by retrieving the changes of body composition, blood pressure, blood chemistries & urine tests, and subjective symptoms & fatigue scores. Results: Demographics of the observed participants were 17 of male and 16 of female. Post-Gamrosu session, -6.89% of body weight, -8.97% of body fat mass were reduced with the nutrition indices being improved (P＜0.001). -8.72% of systolic blood pressure, -39.86% of serum triglyceride, -6.75% of fast blood sugar and -8.12% of waist circumference were improved (P＜0.05). The levels of high sensitivity C-reactive protein (-58.34%), CRP (-43.55%) and eosinophil (-21.30%) showed the significant diminished profiles (P＜0.05). Liver/kidney functions and the standard of electrolytes were maintained within normal range in stable manners. The fatigue scale scores indicated significant lower scores. Conclusions: Taken together, obesity-related clinical outcomes after a modified fasting therapy with Gamrosu were sufficiently feasible and the observed findings should be considered for further prospective clinical studies.