After three days on a keto diet, your body typically starts to enter a state of ketosis, where it starts to burn more fat for fuel instead of carbohydrates. This process can lead to symptoms commonly known as the “keto flu”, which may include headaches, fatigue, irritability, dizziness, nausea, and muscle cramps. These symptoms are usually temporary and often subside once your body becomes more efficient at using ketones for energy.