How Fasting May Cause a Headache

With the busy lives, so many of us lead, it's unfortunate, but not surprising, that eating can sometimes get put on the back burner. And not eating (purposefully or not) can lead to a headache that can further damper your already stressful day.

Let's take a closer look at fasting headaches and how you can prevent them.

Symptoms of a Fasting Headache

People who do not eat for more than 16 hours may develop what is expectedly called a "fasting headache," which according to the third edition of the International Classification of Headache Disorders occurs during the fasting period and resolves within 72 hours of food intake.

In terms of how a fasting headache feels, the pain is typically mild to moderate in intensity, occurs at the front of the head (the forehead), and is non-throbbing. With that, a fasting headache feels more like a tension-type headache than a migraine.

It's interesting to note that the likelihood of a fasting headache developing increases with the duration of the fast.

In addition, in an article in Headache, researchers note that people who normally get headaches are more likely to develop a fasting headache when not eating than people who do not normally get headaches. In other words, if you already have an underlying headache disorder, you may be more vulnerable to the headache effects of fasting.

Cause of a Fasting Headache

The cause of fasting headaches is still controversial. One potential mechanism experts suspect is hypoglycemia or low blood sugar. More specifically, some experts suggest that for certain genetically predisposed people, small changes in blood glucose may alter pain receptors in the brain, leading to a fasting headache.

On the flip side, here is why other scientists do not think hypoglycemia is the cause of fasting headaches:

  • In healthy people, glycogen (the stored form of glucose) levels in the liver are enough to sustain normal glucose levels for 24 hours.
  • A fasting headache may occur in the presence of normal glucose levels.
  • Research shows that insulin-induced hypoglycemia does not produce a headache in migraineurs.
  • Headache is not a symptom of hypoglycemia that urges patients to seek ED care.
  • Hypoglycemia-induced headaches have a pulsating quality while fasting headaches do not.

Caffeine withdrawal has also been linked to fasting headaches, but is also controversial, like hypoglycemia. A caffeine-withdrawal headache generally occurs about 18 hours after the last caffeine intake, similar to that of a fasting headache. In addition, a caffeine-withdrawal headache has features similar to a tension-type headache (like a fasting headache).

Again though, like hypoglycemia, people still get fasting headaches even when they do not consume caffeine, which disputes caffeine withdrawal as a primary cause of fasting headaches.

In fact, many scientists think that like hypoglycemia-induced headaches, a caffeine withdrawal headache is a separate entity from a fasting headache. This is supported by the IHS, which codes these headaches separately.

Other potential causes of fasting headaches that have been proposed include dehydration and the stress that led to the fasting state.

The bottom line here is that the precise cause of fasting headaches is still unknown.

There may be a number of factors involved and/or it could vary for the individual—a unique cause, so to speak.

Treatment of a Fasting Headache

The obvious way to prevent fasting headaches is to not skip meals. That being said, in unexpected circumstances, like with a long work meeting or delayed flight, try to consume even a little food or bite of sugar, as this may be all your body needs to ward off a headache.

On the other hand, if you are fasting for a longer period of time, like for religious reasons, consider reducing caffeine consumption weeks prior to fasting, followed by drinking a strong cup of coffee on the first day of the fast.

Alternatively, you can speak with your doctor about starting a preventive headache medication on the first day of your fast, like a long-acting NSAID. That said, remember to not take any medications, including over-the-counter medications, without the advice of your doctor first.

A Word From Verywell

The exact cause of fasting headaches is largely unknown and very well may involve many factors or be individualized. Regardless, by being attuned to your headache health, you can easily prevent this type of headache by ensuring you are eating regular meals. Of course, if you are fasting for religious or other purposes, please speak with your doctor about the best strategy to prevent a headache.

Sources:

Headache Classification Committee of the International Headache Society. "The International Classification of Headache Disorders: 3rd Edition (beta version)". Cephalalgia 2013;33(9):629-808.

Torelli P, Evangelista A, Bini A, Castellini P, Lambru G, Manzoni GC. Fasting Headache: A Review of the Literature and New Hypotheses. Headache. May; 2009 49(5):744-52.

Torelli P, Manzoni GC. Fasting Headache. Curr Pain Headache Rep. 2010 Aug;14(4):284-91.

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