There are difference in practicing fasting in different religions. Difference may be in form of patterns (continuous versus intermittent) or duration. Although fasting simply defined as intentional abstinence of food, pathophysiology that run behind fasting is similar to starvation ketosis. Case presentation: We observe clinical and laboratory determinants of healthy person who voluntary choose to go on religious fasting of Chaitri for 9 days at Nootan medical college & research center, a rural medical college at Visnagar, Mehsana, Gujarat. He has not taken any food or even water and no any parenteral treatment was given. Routine Laboratory blood investigation was done on day of admission and on daily basis for 9 days. He was closely monitored for vital examinations and any symptoms development every 4 hourly. Results and discussion: On day of admission, he was conscious and no signs of any disease present. On admission, his weight was 76 kg, height was 176 cm, BMI was 24.53 kg/m2 and physical examination was within normal limit. Baseline vital data shows pulse was 68/min, blood pressure was 124/88 mmHg, respiratory rate was 16 per minute and oxygen saturation was 99% on admission. His weight remains stable during whole course of fasting. Increase in pulse rate was noted after 5th day onwards and no significant change in blood pressure noted. There was increase in urine output noted on 5th day of fasting followed by subsequent decrease because of ketosis and natriuretic property of ketone bodies. Routine laboratory blood investigation like complete blood count, renal function test and liver function test was within normal limit on date of admission and there was no significant change during fasting. His fasting blood sugar was 86 mg/dl on admission and decreased to level of 64mg/dl on last day of fasting, however no any symptoms of hypoglycemia was noted. Serum acetone was absent on day of admission but very next day it become positive and remain positive for next eight day of fasting. Urine acetone was trace on 2nd day of fasting and there was increased in grading as fast progress. Hormonal assay of insulin and growth hormone showed decremental response in insulin level and incremental response in growth hormone level. It shows that transition from the food replenished state to fasting and into prolonged starvation is mediated by a series of complex metabolic, hormonal and glucoregulatory mechanisms. Conclusion: The body adapt to long-term fasting by increase in utilization of alternate source of fuel like ketone bodies and sparing need of glucose. The remarkable ability of the body to adapt to long-term starvation has been critical for survival in adverse situation.