How is fasting related to insomnia? Yesterday I started a new diet using intermittent fasting. For this reason I only ate one meal all day. I was pretty surprised how well I passed that day: I studied a lot, did some sports and fulfilled several programming exercises from university. After sports I had my first meal. Overall—a great day without any side effects from the intermittent fasting.

However, at 11 PM I went to bed. There I realized that I was not tired. So I read a book. One hour passed—still no feeling of fatigue. So, I thought, some push ups will make me tired. Nope, the push-ups did not work. It was already 1 AM, and I had to get up early. I decided to use my strongest means, which I only use before big exams: a glass of brandy. No effect! Meditation—nope. After that, 30 minutes of running outside in the cold—again, no effect. At 4 AM I decided to get up and study. 

A weird experience. I know that I lack sleep; nevertheless, I can study and concentrate.

I Googled the keywords fastening and sleeplessness. Then I realized that it is a common pattern that some people sleep less during fasting.

Why is fasting related to insomnia?
Fasting causes stress and makes your body work off of fat rather than sugar. Sugar is of course related to insulin, which even in normal (non-diabetic) people must be maintained at a certain level (Kaditis et al., 2005). Without a proper level of insulin, your body will upregulate orexin in the brain until you eat (Willie, Chemelli, Sinton, &amp; Yanagisawa, 2001). Orexin will give you artificial energy and inhibit sleep.

References

Kaditis, A. G., Alexopoulos, E. I., Damani, E., Karadonta, I., Kostadima, E., Tsolakidou, A., ... &amp; Syrogiannopoulos, G. A. (2005). Obstructive sleep‐disordered breathing and fasting insulin levels in nonobese children. Pediatric Pulmonology, 40(6), 515–523.

Willie, J. T., Chemelli, R. M., Sinton, C. M., &amp; Yanagisawa, M. (2001). To eat or to sleep? Orexin in the regulation of feeding and wakefulness. Annual Review of Neuroscience, 24(1), 429–458.