You may get a fasting headache when you begin intermittent fasting, especially if you already experience headaches regularly. Symptoms will be mild as it takes a few days for the body to adjust to the new eating schedule. Stay hydrated, reduce caffeine intake slowly, and eat plenty of calories with a focus on healthy fats to prevent a headache while fasting.
Intermittent fasting Day One. You’ve passed the 12-hour mark. Normally you’d be feeding yourself at this point, but you are trying to extend the fasting period by a few more hours. Then, out of nowhere, a headache sets in, and you need to decide whether to continue or stop the fast.
Although not everyone will experience a headache while fasting, many people feel some head discomfort the first few days when starting an intermittent fasting program as their bodies adjust to a new eating schedule, especially if they are already prone to headaches.
There are ways to prevent or lessen the effects of a fasting headache.
According to the International Classification of Headache Disorders, there are 2 classes of headaches – primary and secondary.
Primary headaches have no underlying cause or disorder that produces the headache. This includes tension headaches and migraines. Migraines affect 28 million women in the U.S. (1). Fasting may trigger migraines (2). Fasting headaches occur more frequently, with stronger symptoms, for those who already suffer from primary headaches (3).
This pain can be traced to a specific cause, such as a brain tumor or aneurysm. A significant reason for these headaches is the disruption of the body’s natural state of homeostasis, the internal system that regulates bodily functions and maintains stability. Intermittent fasting may cause a homeostasis disruption, leading to a fasting headache regardless of what method of intermittent fasting you choose to follow.
The fasting headaches that are most common and typically last only a few days when beginning intermittent fasting are considered secondary headaches.
If you are new to intermittent fasting, after 16 hours, you may feel a mild-moderate, non-pulsating headache persisting toward the front of the head. This usually goes away within 72 hours of consuming food (4). All headache symptoms should be completely resolved after a week of consistent fasting.
If intermittent fasting for fat burning is your goal, the body needs to stay in a fasted state long enough for blood sugar and insulin levels to drop low enough to trigger the fat-burning hormone glucagon (5).
After years of eating every few hours, the body expects to be fed when it signals to you that it is hungry. If you decide to hold back on eating, the body will let you know it is not happy, and for some women, that means a temporary headache.
Some possible reasons for an intermittent fasting headache include low blood sugar, dehydration, and caffeine withdrawal.
Blood sugar levels drop significantly when fasting. Some research shows that small changes in blood sugar levels may affect pain receptors in the brain for certain people, causing a fasting headache (2).
On the other hand, other research shows that low blood sugar does not cause fasting headaches because, in healthy people, there is enough blood sugar stored for 24 hours. Also, fasting headaches still occur in people when blood sugar levels are normal, and these have a non-pulsating quality, whereas low blood sugar-induced headaches are pulsating (6).
Many people maintain their hydration levels through the foods they eat. When incorporating an intermittent fasting lifestyle, less food is consumed, and dehydration can occur if they aren’t drinking enough water during the fast and feasting times. Dehydration can trigger a headache while intermittent fasting (7).
Although caffeine does not have to be eliminated during the fast, consuming only certain items is allowed if one is doing a clean fast. Many people survive on sugar-laden coffee drinks, and only black coffee is allowed when fasting. Because some can’t (or won’t) give up the cream and sugar extras, they choose to forgo coffee altogether during the fasting window.
Some research links fasting headaches and caffeine withdrawal, saying it occurs about 18 hours after the last caffeine intake and comparing caffeine withdrawal headaches to fasting headaches, appearing as tension in the head (8).
However, reduced caffeine-induced headaches occur even when one is not in a fasted state.
Some people will experience a mild-to-moderate headache when fasting when beginning an intermittent fasting lifestyle. It typically lasts a few days and then resolves itself when consistently following an intermittent fasting schedule.
Low blood sugar, dehydration, and caffeine withdrawal may cause a fasting headache, but headaches will happen with these occurrences regardless of whether one is in a fasted state. Avoid intermittent fasting headaches by focusing on good nutrition, proper hydration, and reducing caffeine consumption gradually.
Intermittent fasting is not all about cons, there are also very positive reasons that comes with it, which you can found in this other article talking about intermittent fasting pros and cons.
Get other solutions for success with intermittent fasting by joining this supportive online group of intermittent fasting women.
1. American Headache Society. https://americanheadachesociety.org/news/migraine-impact-women/#:~:text=Of%20the%20more%20than%2037,of%20migraine%20often%20lasting%20longer.
2. Dalkara, T., Kılıç, K. How Does Fasting Trigger Migraine? A Hypothesis. Curr Pain Headache Rep 17, 368 (2013). https://doi.org/10.1007/s11916-013-0368-1
3. Mosek A, Korczyn AD. Yom Kippur headache. Neurology. 1995;45(11):1953-1955. doi:10.1212/wnl.45.11.1953
4. Torelli P, Manzoni GC. Fasting headache. Curr Pain Headache Rep. 2010;14(4):284-291. doi:10.1007/s11916-010-0119-5
5. Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 30.3, Food Intake and Starvation Induce Metabolic Changes.
6. The International Classification of Headache Disorders, 3rd edition (beta version). Cephalalgia. 2013;33(9):629-808. doi:10.1177/0333102413485658
7. Blau J. Water deprivation: A new migraine precipitant. Headache: The Journal Of Head And Face Pain. 2008. https://doi.org/10.1111/j.1526-4610.2005.05143_3.x
8. 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
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