How Fasting Causes Headaches

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A fasting headache is a type of head pain that occurs after not eating for 16 hours or more. The 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.

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Fasting Headache Symptoms

The "fasting headache" typically happens when people do not eat for more than 16 hours. 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.

In other words, 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.


Click Play to Learn More About Fasting Headaches

This video has been medically reviewed by Rochelle Collins, DO.


The exact cause of fasting headaches is still not known. There are a few theories for why this happens.


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 the fasting headache.

On the other hand, some scientists do not think blood sugar is the cause of fasting headaches. Some of the reasons for why they think this are:

  • 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.

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.

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.


There are a few theories for why fasting headaches happen. They include low blood sugar caused by not eating, caffeine withdrawal, stress, and dehydration. But all of these theories have drawbacks. Science is still working to understand the reason for why these headaches happen.


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, people should 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. It may help to limit caffeine use in the weeks prior to fasting. Or, you can speak with a healthcare provider about preventing headaches with medication, such as a long-acting nonsteroidal anti-inflammatory drug (NSAID).


A fasting headache can feel like a tension headache. Scientists still don't know the exact reason for 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.

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4 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.
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  2. Dalkara T, Kiliç K. How does fasting trigger migraine? A hypothesis. Curr Pain Headache Rep. 2013;17(10):368. doi:10.1007/s11916-013-0368-1

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  4. Torelli P, Evangelista A, Bini A, Castellini P, Lambru G, Manzoni GC. Fasting headache: a review of the literature and new hypotheses. Headache. 2009;49(5):744-52. doi:10.1111/j.1526-4610.2009.01390.x

By Colleen Doherty, MD
 Colleen Doherty, MD, is a board-certified internist living with multiple sclerosis.