If you don't get enough, you can have symptoms such as fatigue, dizziness, constipation, dehydration, and not being able to tolerate cold temperatures. Fasting too long can be life threatening. Don't fast, even for a short time, if you have diabetes, because it can lead to dangerous dips and spikes in blood sugar.

What happens if you fast too much?

If you want to increase your fasting period to more than 72 hours, you should seek medical supervision. Summary Longer periods of fasting increase your risk of side effects, such as dehydration, dizziness and fainting. To reduce your risk, keep your fasting periods short.

Can you overdo fasting?

However, if you continue to feel tired or to have low energy levels during your fasting window several weeks into your new schedule, you may be overdoing it. You may be trying to fast for too long for too often, or not getting enough calories in during your eating windows.