You may get “keto flu”
Keto flu is a real thing. Cutting your carbs to the bone and going into a state of ketosis (where your body burns fat for energy) can bring on a cluster of uncomfortable symptoms, such as headaches, fatigue, muscle aches, nausea, and diarrhea. The side effects are the result of your body transitioning to using fat as its primary source of energy instead of carbs, explains Kristen Mancinelli, M.S., R.D.N., author of The Ketogenic Diet. Once it adapts to the new fuel source (usually within a week or two), you’ll start to feel better.
Your mood can fluctuate
When you’re on a low carb diet you may not be getting the carbohydrates needed to produce serotonin, a brain chemical that helps regulate mood, as well as sleep and appetite—two other factors that can mess with your disposition, says Laura Iu, R.D., registered dietitian and nutrition therapist certified intuitive eating counselor based in New York City.