"Fasting is so interesting, because if you really think about it from an evolutionary perspective, fasting was always part of our life," Dr. Arad told POPSUGAR. He explained that because of this, the body has different mechanisms that allow it to handle fasting particularly well. Whether or not fasting is healthy is up for debate, he explained, noting that some studies suggest that fasting could improve your metabolism, your insulin sensitivity, and "different markers that relate to longevity and to health and wellness."
According to Dr. Arad, your body typically goes into fasting mode after eight to 12 hours, but this depends on how much glucose you have in your blood and how long it takes to deplete the sugar stored in your liver. Once your body hits fasting mode, "it's trying to conserve the little amount of sugar that we have, and it's really trying to rely on fat," he explained.