Brain & Nervous System Headaches Causes & Risk Factors How Fasting Causes Headaches By Colleen Doherty, MD Updated on November 07, 2023 Medically reviewed by Nicholas R. Metrus, MD Print Table of Contents View All Table of Contents Symptoms Causes Prevention A fasting headache is a type of head pain that occurs after not eating for 16 hours or more. You may experience a headache when you skip meals, while practicing intermittent fasting, or when fasting for religious reasons such as Ramadan. A fasting headache is usually mild to moderate and does not throb or pulse. Fasting headaches may be felt all over the head (diffuse), or the pain may centralize around the forehead. Fasting headaches are linked to low blood sugar (hypoglycemia) and dehydration. They can also be associated with caffeine withdrawal. The headache usually goes away after eating. This article discusses fasting headaches. It reviews the potential causes of fasting headaches and ways to prevent them. Pongtep Chithan / Getty Images Fasting Headache Symptoms A fasting headache typically happens when people do not eat for eight hours or longer. The good news is that when you start eating again, the headache will go away within 72 hours. The headache pain is typically mild to moderate in intensity. It is located at the forehead, and it does not throb. So a fasting headache feels more like a tension headache than a migraine. Still, fasting can induce a migraine in people who have migraine headaches. Not eating may cause a fasting headache or it can be a trigger for a migraine. The longer you go without eating, the more likely it is that a fasting headache will occur. Research also supports the finding that people who normally get headaches are more likely to develop a fasting headache than those who do not. 1:38 Click Play to Learn More About Fasting Headaches This video has been medically reviewed by Rochelle Collins, DO. Causes The exact cause of fasting headaches is still not known. There are a few theories for why this happens. Hypoglycemia One possible cause for fasting headaches is hypoglycemia, or low blood sugar. For some people with a certain genetic makeup, small changes in blood sugar may affect pain receptors in the brain. This leads to a fasting headache. On the other hand, some scientists do not think blood sugar is the cause of fasting headaches because: Glycogen is the body's storage form of glucose. In healthy people, glycogen levels in the liver are enough to sustain normal blood sugar levels for 24 hours.A fasting headache may happen even if the blood sugar levels are normal.Low blood sugar related to insulin use does not cause a headache in people who get migraines.Headache is not a symptom of low blood sugar that causes people to seek emergency care.Hypoglycemia-induced headaches have a pulsing quality while fasting headaches do not. Headache From Low Blood Sugar Caffeine Withdrawal Caffeine withdrawal also has been linked to fasting headaches. This, like the blood sugar link, is controversial too. A caffeine-withdrawal headache usually occurs about 18 hours after the last caffeine intake. This is similar to the pattern seen in a fasting headache. In addition, a caffeine-related headache has symptoms similar to a tension-type headache and a fasting headache. However, people still get fasting headaches even when they don't regularly consume caffeine. This suggests that caffeine withdrawal isn't a primary cause of fasting headaches. In fact, many scientists think that a caffeine withdrawal headache is a separate entity from a fasting headache. Indeed, these headaches are coded separately in the system that medical researchers use to classify headaches. Causes of a Caffeine Withdrawal Headache and How to Fix It Dehydration or Stress Other causes of fasting headaches have been proposed too. They include dehydration and stress. Sometimes, stress is what causes people not to eat in the first place. The bottom line here is that the precise cause of fasting headaches is still unknown. There may be a number of factors involved. It also may vary for each individual. Understanding Dehydration as a Headache Trigger Headaches From Intermittent Fasting Intermittent fasting is an eating plan that includes scheduled periods of normal eating followed by scheduled periods of fasting. There are several different intermittent fasting protocols. Depending on which one you're following, you may experience a headache as one of the side effects of fasting. For example, some people participating in alternate-day fasting programs have reported headaches in the first few days of following the eating schedule. These headaches tend to be mild and are more common in the early days of following the plan. They usually resolve once you start eating again. If you do experience a headache during intermittent fasting, it may help to increase your water intake. Studies have found that headache is the most common side effect in people following an intermittent fasting program, with mild headache occurring in 36.1% of cases, moderate headache in 17.7% of cases, and severe headache reported in 7.5% of cases. Research hasn't determined which intermittent fasting diet protocols are more likely to cause headaches, but generally speaking, the longer the fasting period the more likely you are to experience a headache. Prevention The obvious way to prevent fasting headaches is to not skip meals. Even when something comes up, like a long work meeting or delayed flight, try to eat a little food or a bite of sugar. This may be all your body needs to ward off a headache. Some people fast for religious reasons. This often means going a much longer time without food and water. Religious fasts may not allow for eating or drinking even small amounts in order to ward off a headache. Headaches during religious fasts may be related to hypoglycemia or to dehydration and caffeine withdrawal. If you drink caffeine regularly during non-fasting days, it may help to limit caffeine use in the weeks before you start fasting. Make sure you are also well-hydrated before beginning a period of abstaining from water and other liquids. If headaches during a religious fast are a problem for you, you may want to speak with a healthcare provider about preventing headaches with medication, such as a long-acting nonsteroidal anti-inflammatory drug (NSAID). Since fasting headaches are more common in people with a history of migraines, taking an abortive migraine medication before fasting may help. Water Fasting: What You Need to Know Summary A fasting headache can feel like a tension headache. Scientists still don't know the exact reason why not eating can cause a headache. It does seem to happen more in people who get headaches routinely. The best thing you can do is to eat normal meals that keep your energy and your blood sugar levels steady and watch your caffeine intake. Headaches Doctor Discussion Guide Get our printable guide for your next doctor's appointment to help you ask the right questions. Download PDF Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Email Address Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. 9 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Soares AA, de Vasconcelos CA, Silva-Néto RP. Headaches and food abstinence: a review. J Clin Case Stud. 2018;3(1). National Headache Foundation. The complete headache chart. Al-Hashel JY, Abokalawa F, Toma R, Algubari A, Ahmed SF. Worsening of migraine headache with fasting Ramadan. Clin Neurol Neurosurg. 2021 Oct;209:106899. doi:10.1016/j.clineuro.2021.106899 Salim A, Ilyas MA, Rizvi M, et al. Fasting headache, a cross-sectional study. Int J Res. 2015;2(8):379. Headache Classification Committee of the International Headache Society (IHS). The International Classification of Headache Disorders, 3rd Edition. Cephalalgia. 2018;38(1):1-211. doi:10.1177/0333102417738202 Cui Y, Cai T, Zhou Z, et al. Health effects of alternate-day fasting in adults: A systematic review and meta-analysis. Front Nutr. 2020;7:586036. doi:10.3389/fnut.2020.586036 Morales-Suarez-Varela M, Collado Sánchez E, Peraita-Costa I, Llopis-Morales A, Soriano JM. Intermittent fasting and the possible benefits in obesity, diabetes, and multiple sclerosis: A systematic review of randomized clinical trials. Nutrients. 2021;13(9):3179. doi:10.3390/nu13093179 Shalabi H, Hassan AS 4th, Al-Zahrani FA, et al. Intermittent fasting: Benefits, side effects, quality of life, and knowledge of the Saudi population. Cureus. 2023;15(2):e34722. doi:10.7759/cureus.34722 Diamond S. The fasting headache. National Headache Foundation. By Colleen Doherty, MD Dr. Doherty is a board-certified internist and writer living with multiple sclerosis. She is based in Chicago. See Our Editorial Process Meet Our Medical Expert Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit