You can eat before donating blood, and you must eat before donating blood and avoid giving blood on an empty stomach. This is because if you donate blood on an empty stomach, blood sugar may drop, causing the donor to experience discomfort such as dizziness, weakness and panic, or in severe cases, hypoglycemic coma and convulsions, so you must not fast before donating blood. In addition, the night before the blood donation, you should pay attention to avoid high sugar, high fat and greasy food in your diet, and avoid cloudy blood when you donate blood the next day, otherwise the quality of blood donation will be affected. Also make sure to get enough sleep before donating blood and not to be overly stressed. Do not donate blood if you have a recent cold or other discomfort. It is more appropriate to donate blood after the cold has subsided.