Keto flu symptoms can start to kick in within a day or two of adopting a ketogenic diet, Mancinelli says. If you recently cut your carbs below 50 grams daily and soon notice that you feel downright awful, you’ve probably got a case of keto flu.
That’s not to say everyone starting out on a keto diet ends up wholly incapacitated for days. “You might find that you fatigue more quickly or that exercise seems harder than normal,” says Seattle-based nutritionist and Academy of Nutrition and Dietetics spokesperson Ginger Hultin, MS, RDN. Your body might also have an easier time transitioning (read: fewer symptoms) if you were already eating a relatively low-carb diet, Mancinelli explains.
Is keto flu dangerous? Do I need to call my doctor?
Adopting a keto diet for the short term is generally considered safe, and any symptoms you might experience will typically clear up within a couple weeks, Hultin explains. (The jury’s still out on how eating this way might impact your body long-term.)