Fasting before blood work means you shouldn’t eat or drink anything except water for at least eight hours before a blood test. For some tests, you may need to fast for 12 hours. Ask your health care provider how long to fast before your blood test if you’re unsure. Besides food, you should also avoid chewing gum and mints. This is what you need to know to do 16/8 intermittent fasting. Choosing a time window. To get started, begin by picking an 8-hour window and limiting your food intake to that time span. 18/6. 18/6 intermittent fasting is a type of time-restricted eating where you fast for 18 hours and eat within a 6-hour window each day. Other popular TRE methods include 12/12 and 14/10, and you can go off script here, too, to try something like 15/9 if it fits better! Yk0Oaw.