This occurs when someone switches their diet from one that is carb-heavy to a diet with a dramatically reduced carb intake. People can experience headaches, tiredness or exhaustion and an inability to think clearly. Often, people will take to bed thinking their body needs rest. This is not strictly true.
What is happening is that, when given a choice, the body will burn carbs for energy. When an individual switches from a diet plentiful in carbs to one with greatly reduced carbs, the body is perplexed. It is used to burning carbs for energy and doesn’t naturally switch to burning fat when no carbs are present. This can lead to an insatiable hunger in someone who should not be hungry, but their body is craving energy and it needs carbs for energy.
Fortunately, the body is not meant to rely solely on carbs for energy. In the absence of carbs, it is perfectly capable of burning fat for energy…the problem is that many of our bodies are quite out of this habit. When we switch to a low carb diet, there is a period of adjustment as our bodies remember what it is they’re supposed to do!
Most people have an imbalanced diet that is heavily weighted towards carbs. The change to a diet lacking in carbs will prove a challenge to our bodies, at least in the short term. However, once that period of adjustment is over, you will feel the difference and lose your carb cravings. Imagine your computer is running slowly and you give it a factory reboot - that is what is happening inside you.
The level of the low carb flu that you experience will depend on a number of factors, but that doesn’t mean that you should make yourself seriously ill going through the process.