Can fasting cause headache?

Headache attributed to fasting is a diffuse non-pulsating headache, usually mild to moderate intensity, occurring during and caused by fasting for at least eight hours. The headache is relieved after eating. Headache sufferers have a higher risk of developing headache during fasting than people who do not have history of a primary headache disorder. In patients with migraine without aura, fasting can also be a trigger for migraine headache. 

Headache attributed to fasting has been reported in prolonged religious fasting such as during Yom Kippur and Ramadan.