The keto flu is not really a virus. It's just a side effect of the keto diet that some people get. It usually includes a feeling of exhaustion, cramps, and sometimes even headaches. The keto flu is usually caused by the body trying to adjust to a new fuel source and/or an electrolyte imbalance. Adding salt and other electrolytes to the diet helps as well as increasing the intake of healthy fats such as avocados, olives, macadamia nuts, and eating more green leafy vegetables. This typically goes away on its own with patience and an improved diet and by adding extra salt to your food.