The effect of diet on test results It is common knowledge that you need to fast to have blood drawn, but why do you need to fast? How long do you need to fast? Many people are not very clear about this. That is because diet or fasting for too long can affect the results of many tests, such as after a standard meal: triglyceride increases by about 50% bilirubin, sugar increases by about 15%, alanine transferase increases by about 10%, total protein, albumin increases by about 5% bilirubin, inorganic phosphorus, calcium, sodium and cholesterol increases by about 5% high fat diet will make triglycerides rise significantly high protein diet will make ammonia, uric acid Therefore, it is required to fast for 12 hours before the blood draw and to eat a light diet for the first three days, preferably in the morning. However, if patients fast for too long, serum albumin, complement c3, transferrin, and glucose levels may decrease, and serum bilirubin may increase due to decreased clearance.