Skipped meals, fasting and migraine

What studies show

• Self-report. Not eating was the third most named trigger among 1,207 clinic patients, at 57.3% (Kelman 2007).
• Diary study. 30 patients in Israel kept migraine diaries during Ramadan and the following month. They had 9.4 ± 4.3 migraine days during the fast and 3.7 ± 2.1 in the control month (p under 0.001). Fluid and caffeine intake were not measured, so the increase cannot be assigned to lack of food alone (Abu-Salameh 2010).
• Case-control study. Women with migraine more often ate fewer than 3 meals a day (29.4% vs 9.4%) and had irregular meal schedules (37.6% vs 23.5%) than controls (Nazari 2010, reported in Hindiyeh 2020). This shows an association, not its direction.
• Reviews. A review lists fasting among the triggers supported by clinical studies (Marmura 2018). A systematic review rated the overall quality of diet-trigger evidence as low and found no randomised trials of diet as a trigger (Hindiyeh 2020).

This evidence comes from observation, not from trials that assign fasting.

Fasting headache in ICHD-3

ICHD-3 lists a separate diagnosis, headache attributed to fasting (10.5). It is a diffuse, non-pulsating headache, usually mild to moderate, that develops during a fast of at least 8 hours and improves after eating. It does not meet the criteria for migraine. An attack that does meet them is coded as migraine, with fasting as the precipitating factor. Fasting headache is more common in people with a primary headache disorder, and the chance rises with the length of the fast.

So a headache during a fast is not always a migraine attack. Record the features as well as the time.

Why it might happen

The cause is not established, and sources differ.

• Blood sugar. The Migraine Trust says missing meals lowers blood sugar. ICHD-3 states that there is no conclusive evidence for a causal link with hypoglycaemia: fasting headache can occur without it, and insulin-induced hypoglycaemia does not precipitate headache in people with migraine.
• Brain energy supply. One proposal is that low glucose supply during intense synaptic activity sets off a network depolarisation that activates trigeminal nerve fibres. Its authors present this as a hypothesis (Dalkara 2013).
• Related factors. The Ramadan study’s authors link fasting headache to dehydration and caffeine withdrawal, but did not measure either (Abu-Salameh 2010). ICHD-3 says that headache attributed to fasting does not appear to be related to caffeine withdrawal.

How to check it in your diary

1. Log meal times, and the gap between your last meal and the start of each attack.
2. Log drinks in the same gap. A missed breakfast can also mean a late coffee and less fluid.
3. Ask why the meal was missed. Nausea is a prodrome symptom. A meal skipped because you felt unwell may be part of the attack, not its cause.
4. Count long gaps with no attack.

The Migraine Trust advises regular mealtimes and not going too long without eating. For the general method, see how to test a suspected trigger.

When to see a doctor

If you plan to fast, for religious or other reasons, raise it with your doctor in advance. A 2021 review advises clinicians to ask about fasting and to plan treatment around it (Arca 2021).