Fasting and Migraine: Why Fasting Can Trigger Headaches and How You Can Prevent Them

Maybe you know this moment.

If you recognize yourself here, you are in good company. Headache is one of the most common complaints during fasting. And if you live with migraine, the worry about fasting is often bigger than the hunger.

I want to give you more than a shrug. This article is about three questions. How common are headaches during fasting? Which factors has research identified? And what can you prepare so that your head stays calmer?

How to ease gently into fasting is covered in Fasting for beginners. What coffee does to your fast is explained in What breaks a fast? This article is about your head.

Is a headache during fasting normal? What studies show about how common it is

In short: Headache during fasting is common. In studies on religious fasting days, around four in ten people who fasted developed headaches, compared with fewer than one in ten of those who did not fast. The risk rises with the length of the fast and is clearly higher in people with a history of headaches. Typical is a pressing headache on both sides that improves after eating.

Maybe you wonder whether something is wrong with you because others seem to fast effortlessly. The numbers tell a different story.

In this study, the pain was mostly non-throbbing, mild to moderate, on both sides and at the forehead. With every hour of fasting, the number of people affected rose. A survey of hospital staff in Riyadh painted a similar picture on the first day of Ramadan. Of those fasting, 41 percent had headaches, but only 8 percent of those not fasting. In 78 percent of cases, the pain resembled a tension-type headache.

The International Classification of Headache Disorders therefore lists headache attributed to fasting as a diagnosis in its own right. A review from Parma describes it as diffuse or concentrated at the forehead, non-throbbing and mild to moderate. In a Danish population study, 4.1 percent of people had experienced it at least once in their lives. It usually subsides within 72 hours after you start eating again.

The pattern repeats: the beginning is the hardest phase. In a study from Riyadh with 173 participants analyzed, 33 percent had headaches on the first day of Ramadan, and by the seventh day it was 11 percent. A recent review from Denmark describes the same thing. Symptoms are strongest in the first days of fasting and usually ease afterwards.

And now you know why the first day of fasting is rarely a good yardstick for your fasting.

Where do headaches during fasting come from? Five factors instead of one culprit

Maybe you have read that fasting headache is simply low blood sugar. Or dehydration. Or detox. Each of these explanations sounds convincing. None is enough on its own.

So far, research has not found a single trigger. A review from Parma names low blood sugar and caffeine withdrawal as particularly debated causes and emphasizes that much remains open. A 2026 review of 20 studies on Ramadan lists lack of fluids, caffeine withdrawal, low blood sugar, disrupted sleep and changed eating habits. The International Classification of Headache Disorders is even more cautious. It states that fasting headache can also occur without low blood sugar.

Imagine your head as a set of scales. On one side lies your sensitivity to pain. On the other side lie small weights: the missing coffee, one glass of water too few, a short night, an empty sugar store. Each weight alone would be no problem. Together, the scales can tip.

Seen through the lens of Clinical Psychoneuroimmunology, four systems interlock here. None of them works alone.

And now you know why a single explanation for headaches during fasting is rarely enough.

Caffeine withdrawal: why your morning coffee has a say when you fast

Do you remember a morning without coffee? By midday your head felt heavy and your patience was short. The same often happens when you fast. Only this time, you don't recognize it as a coffee problem.

In the brain, caffeine occupies the docking sites for adenosine, a messenger that makes you tired and can widen blood vessels. Put simply: your brain gets used to its daily caffeine shield. If that shield suddenly disappears, adenosine can act unchecked, and your head speaks up.

A large review from the US analyzed 57 experimental studies and 9 survey studies on caffeine withdrawal. In the experiments, headache occurred in half of the participants. Symptoms usually began 12 to 24 hours after the last caffeine, peaked after 20 to 51 hours and lasted two to nine days. Even giving up 100 milligrams a day, about one cup of coffee, could trigger symptoms.

Put these times next to a fasting day. If you drink your last coffee on the morning before you start fasting, the onset of possible withdrawal symptoms falls right into your first day of fasting.

In the survey from Riyadh, caffeine withdrawal was the most important external factor for headache on the first day of Ramadan. The authors suggested gradually reducing coffee intake in the weeks before Ramadan and drinking one more strong coffee right before the fast begins.

In people with migraine, abrupt withdrawal can hit particularly hard. In a small Norwegian study, participants consumed an average of around 540 milligrams of caffeine a day. The unnoticed switch to placebo triggered severe migraine attacks in 7 of 9 participants. The study was stopped early due to a lack of participants and is therefore only an indication.

More is not better, though. In a diary study from Boston with 98 people with migraine, the number of caffeinated drinks was not uniformly linked to migraine on the same day. The researchers interpret their data to mean that mainly larger amounts could be a trigger.

And now you know why coffee deserves its own place in your fasting plan.

Blood sugar, ketones and a hungry brain: how much truth is there in the low blood sugar theory?

Shaky hands, irritability, a head wrapped in cotton wool. Many people immediately interpret this as low blood sugar. The feeling is real. The explanation is more complicated.

In healthy people, the body keeps blood sugar within range remarkably well during fasting. In a large observational study from the Buchinger Wilhelmi clinic with 1,422 people, blood sugar during therapeutic fasting dropped on average into the low normal range. At the same time, ketone bodies rose, a sign of the metabolic switch. Fewer than one percent of participants reported side effects.

An older study from 1971 fits this picture. There, artificially induced low blood sugar triggered migraine-like symptoms in only 2 of 20 people with migraine. So in healthy people who fast, true low blood sugar is probably rarely the main reason.

Energy still plays a role, though. A review in Nature Reviews Neurology describes migraine as a possible response of the brain to a mismatch between energy reserve and workload. According to this view, the attack could even be an attempt to restore the energy balance in the brain.

Imagine your brain as a data center that needs power around the clock. If the usual supplier fails, a backup generator kicks in: ketones. Switching over takes time. In that gap, a sensitive system can sound the alarm more quickly.

People experience a similar switch when they start a ketogenic diet. An analysis of online forums with 300 users found headache among the most common complaints of the so-called keto flu. Reports clustered at the beginning and became less frequent after four weeks.

The flip side is interesting. In an Italian observational study with 96 women with overweight and migraine, a very low calorie ketogenic diet lowered the number of attacks from 2.9 to 0.71 per month after one month. During the transition back to a normal diet, symptoms temporarily increased again. So ketosis itself does not seem to be the problem, but rather the transition.

And now you know why, with blood sugar, it is less about the lowest value than about the transition.

Water and salt: why your head can ask for salt when you fast

You get up from your desk, feel lightheaded for a moment, and your head is pounding. But you've had enough to drink. Haven't you?

The role of water is surprisingly controversial. In a follow-up study from Tel Aviv, 56 women weighed themselves before and after the 25-hour fast of Yom Kippur. Those who developed headaches had lost 1.4 kilograms on average, those who didn't, 1.2 kilograms. The difference was not statistically significant. The researchers concluded that dehydration on a single fasting day is probably not the main cause.

At the same time, lack of water is a well-known headache trigger. In a London case series, about one in ten people surveyed reported headache when short of fluids. In 22 of 34 of those affected, it disappeared within 30 minutes after they drank half a liter on average.

And salt? This is where it gets physiological. In the first days of fasting, the kidneys excrete more sodium. This phenomenon has been described as the natriuresis of fasting since the 1970s at the latest. A paper in the New England Journal of Medicine examined the role of renin, aldosterone and glucagon in it. Water leaves along with the sodium. This can strain your circulation, especially when you stand up.

Imagine your circulation as a garden hose. If water and salt are missing, the pressure in the hose drops. Your body compensates for this, but during the transition phase it doesn't always manage right away.

What risks longer water-only fasting can pose for your salt balance is covered in Water fasting: potential benefits and risks.

And now you know why a glass of water is sometimes enough and sometimes it just isn't.

Magnesium: a foundation, not a fire extinguisher

Maybe there's already a pack of magnesium in your kitchen drawer, bought for calf cramps or stress. And maybe you've read that it is also the remedy for headaches during fasting.

For the individual fasting day, the data are thin. In the blood test study from Riyadh, magnesium levels were the same in people fasting with and without headache. So an acute magnesium deficiency as the trigger of fasting headache has not been shown.

For migraine overall, the picture is different. The evidence-based guideline of the American Academy of Neurology and the American Headache Society rates magnesium as probably effective for preventing migraine, at the second-highest level of evidence.

Why might magnesium play a role in the head? It sits like a bouncer in certain docking sites for the excitatory messenger glutamate. In this way, it can help keep nerve cells from firing too easily. Based on current knowledge, it is still not a weapon against acute fasting headache.

And now you know why magnesium, if anything, is a building block for everyday life and not an emergency remedy.

If you have migraine: why fasting can be a stronger trigger for you

You know your migraine. You know how the day before feels. Maybe you have learned not to skip any meals because the price was too high. And now you read everywhere how healthy fasting is supposed to be.

A survey across 14 countries paints a similar picture. An existing headache disorder, especially migraine, was more closely linked to headaches during fasting than the lifestyle factors recorded. The attacks came mainly in the afternoon, shortly before breaking the fast, and improved after eating in 54.6 percent of cases.

One observation from migraine research may change how you see this. Premonitory symptoms can begin hours to days before the headache, as a review in Nature Reviews Neurology describes. These include tiredness, yawning, sensitivity to light and noise, thirst and food cravings. So the craving before an attack may already be part of the attack, rather than its trigger.

That can take some weight off your shoulders. Not every hunger followed by a migraine was its trigger. Sometimes the hunger is already the first chapter of the same story.

There is also a trail at the level of messenger substances. In the study from Riyadh, CGRP was elevated in people fasting with headache. Dedicated migraine medications now target CGRP and its receptor, and a review of headache medicine counts them among the major innovations of recent years. Whether such medications make sense around fasting is a question for your neurologist.

An over-the-counter extended-release painkiller, by contrast, showed no clear overall effect across the first week of Ramadan in a study from Riyadh. So medication is no substitute for preparation.

And now you know why fasting with migraine shouldn't be a test of courage, but a planning task.

What is proven, what is plausible and what I observe

With a topic that has so many factors, a clear separation matters to me. Not everything that makes sense has been studied equally well.

Fasting can give you room to breathe: fewer snacks, more calm in your metabolism, more feeling for your body. If every fasting day ends with a headache, that freedom turns into mere deprivation. That is why preparation is worth it.

How you can help prevent headaches during fasting: three levers for your next fasting day

You don't have to change everything at once. These three levers focus on the areas where studies and physiology offer the most clues.

And now you know why good preparation can often achieve more during fasting than sheer endurance.

Warning signs: when a headache during fasting needs medical evaluation

Most headaches during fasting are unpleasant but harmless. Some signs, however, suggest that something other than fasting may be behind them.

Diabetes is a special case. If you take insulin or sulfonylureas, fasting can trigger true hypoglycemia, and headache can be one of its signs. In a study from New Zealand in people with type 2 diabetes, the rate of hypoglycemia roughly doubled on fasting days, even though medication had been reduced beforehand. Experts therefore recommend approaching fasting with diabetes under medical supervision and with your own blood sugar monitoring. You can read more in Fasting with type 2 diabetes.

Fasting is also not something to try on your own during pregnancy and breastfeeding, with a current or past eating disorder, or for children and adolescents.

And now you know when a fasting headache is simply unpleasant and when it deserves a medical evaluation.

Frequently asked questions about headaches during fasting and migraine

Whether fasting has anything to do with detoxification at all is covered in Fasting as detox: autophagy instead of slag.

Where this topic touches other areas

Headaches during fasting touch your nervous system, metabolism, fluid balance and daily rhythm. If you want to dig deeper, these neighboring topics from other guides are worth a look.