Upavasa, or fasting, is the practice of denying oneself food and water. This is an ancient spiritual practice that has fallen into disuse. As stated by Charaka in his Charaka Samhita, Upavasa is one of the spiritual therapies and a type of langhana (that which produces lightness of the body) therapy. If properly practiced, it keeps our minds calm and gives us control over our senses. The eleventh day of each ascending and descending moon, known as Ekaadashi, is when the majority of people in Bhaarata observe fasts. It is a form of intermittent fasting (IF) that triggers metabolic switching, autophagy, etc. Studies have demonstrated that it has a wide range of positive health effects, including type-2 diabetes reversal, an increase in energy, and weight loss. It is an inexpensive technique to raise ketone bodies, lower lipids, and lower blood sugar levels. Additionally, it slows or stops the progression of illness and ageing. Modern researchers are also studying how fasting affects the body's metabolic processes. This paper intends to elucidate the biochemical aspects of fasting .i.e., the metabolic switch and the autophagy.