Toxicological, biological and clinical studies showed that high-purity stevia leaf extract sweetener, called steviol glycosides, is generally recognized as safe for all individuals, including children, pregnant women and individuals with diabetes. It has been approved by the U.S. Food and Drug Administration (USFDA) for the antioxidant and antidiabetic properties. 

Governing bodies such as Food and Agriculture Organization of the United Nations (FAO), World Health Organization (WHO) and Food and Drug Administration (FDA) have also established an Acceptable Daily Intake (ADI) of 4 mg/kg of body weight per day. This equates to approximately 12 mg of high-purity stevia extracts/kg of body weight per day. However, whole-leaf stevia and raw stevia extract for use in processed foods and beverages are not approved by USFDA due to a lack of safety information. 

Human saliva which contains amylase enzyme is not able to hydrolyze the glycosidic bonds present in stevioside. However, the gut microbiota of human is able to degrade stevioside to steviol. This is because Bacteroides species are primarily responsible for the hydrolysis of steviol glycosides in the gut. The released sugar moieties are not absorbed and are most likely quickly utilized by the gut microbes as an energy source, thus making it a zero-calorie sweetener. After that, steviol is transported to the liver where it is conjugated with glucuronic acid to form steviol glucuronide which is then excreted in urine. Thus, it doesn’t cause blood sugar spikes.