While a bagel may seem like a safe morning staple, according to health expert, author, and certified nutritionist Samantha Heller, white grains, especially when ingested without protein, can cause a spike in blood sugar. Your body reacts by pulling your blood sugar down, causing you to feel lethargic. So while that morning bagel may fill you up and give you a momentary sense of well-being, you’ll regret it an hour later when you’re tired, cranky, and you forget the client’s name (again) on your 11 a.m. conference call.