There are many reasons why you may find yourself fasting for an extended period of time. Maybe you are trying intermittent fasting or have an upcoming blood test and your doctor has told you to fast. You could be celebrating a religious holiday that includes fasting, such as Ramadan, or maybe you accidentally fasted because it’s a wild day and you didn’t have a second to eat (I’ve been there, you did!).
Regardless of the reason because if you haven’t eaten, there’s a real chance you’ve experienced one of the not-so-great side effects of fasting: headaches.
Fasting-related headaches tend to be more common among people who suffer from headaches in general, says Jennifer Maeng, RD, consultant to personalized supplement company Twinlab and founder of Chelsea Nutrition. These headaches usually occur after fasting for more than 16 hours. However, it’s certainly possible to experience a fasting-related headache when you’ve abstained from eating for less time.
This is partly because there are several reasons why fasting headaches occur. Here’s what you need to know about fasting headaches, including what’s behind it and how to get rid of it, according to dieticians.
What are the causes of fasting headaches?
There are some probable culprits behind fasting headaches, from dehydration and changes in blood sugar to caffeine withdrawal.
“When your body becomes dehydrated, the blood vessels shrink,” says Reda Elmardi, RD, CSCS, owner of The Gym Goat. This causes the tissues in your body, including the brain, to contract or contract. And when your brain contracts, it moves away from the skull, putting pressure on the nerves and causing pain, according to the Cleveland Clinic. For this reason, even mild dehydration can cause headaches.
And drinking water may not be enough. People typically get about 20 percent of the water they need from food, according to the Academy of Nutrition and Dietetics. So, if you’re not eating, you’ll likely need to drink more water than usual to make up for the fluid you’re not getting from food.
If you are drinking enough water, it is still possible to become dehydrated while fasting due to an electrolyte imbalance. Electrolytes are minerals (ex: sodium, potassium, magnesium) in your body that are important for balancing the amount of water in your body, moving nutrients into your cells and ensuring that your nerves, muscles, heart and brain can function properly. , according to the National Library of Medicine (NLM). Your electrolyte levels naturally fluctuate, but they can get too low or too high due to changes in the amount of water or electrolytes in your body. Most people get enough electrolytes from food or drink, but if you don’t eat (and / or drink) for long periods, your electrolyte levels can get out of balance. “Fasting for more than 12 hours or following a diet that mimics quickly (such as the ketogenic diet) will put you at greater risk of dehydration and electrolyte balance,” because it causes your kidneys to excrete sodium and potassium, says Maeng. If your body excretes these two electrolytes, it could cause imbalance, which can lead to dehydration or overhydration, both of which can give you headaches, according to the NLM.
Plus, “when your body doesn’t get enough water, it starts producing less serotonin, a neurotransmitter that helps regulate moods and sleep patterns,” says Elmardi. Changes in serotonin are believed to potentially trigger tension headaches as well as migraines, a neurological disorder that often includes headache as a characteristic symptom. So that dehydration-induced drop in serotonin can cause migraines, headaches, or even mild depression during the day, Elmardi says.
In addition to serotonin, changes in other hormones such as cortisol (commonly known as the stress hormone) are also a common cause of headaches, says Lisa Powell, MS, registered dietitian at Canyon Ranch in Tucson, AZ, and the Research shows that fasting increases both the level and frequency of cortisol secretion.
Then there is the blood sugar. One of the main reasons behind fasting headaches is fluctuations in blood sugar or hypoglycemia (aka low blood sugar), says Maeng. The brain’s two most important sources of energy are oxygen and sugar (aka glucose, which comes from food and is transported to the brain through the blood, hence the name “blood sugar”), according to the National Headache Foundation. When these energy sources are too low (such as when fasting, and therefore not giving the body glucose to use), the brain reacts to try to restore them, which can cause headaches, dizziness, weakness, headache and sweating. You may also experience throbbing headaches from fasting, which is “due to small changes in blood sugar that affect pain receptors,” says Maeng.
Finally, a fasting headache could be due to caffeine withdrawal if you’re used to drinking caffeine in the morning and are now skipping it due to fasting, says Maeng. Research has shown that caffeine withdrawal headaches are triggered by a change in blood flow in the brain. Since caffeine causes blood vessels to constrict, stopping caffeine consumption allows blood vessels to open, increasing blood flow. This sudden change can cause those painful withdrawal headaches.
What can you do for a fasting headache?
There is good news: “It usually disappears once you eat,” says Maeng. That said, if you’re suffering from fasting headaches and are preparing to eat, dig strategically. “Your first meal after fasting shouldn’t be a large simple carb meal like a large bowl of pasta, bread, rice or noodles,” she says. “Eating a large amount of simple carbohydrates can raise your blood sugar and potentially lead to overproduction of insulin and lead to another episode of hypoglycemia. If this continues to occur throughout the day (eating simple carbohydrates all day), it can affect levels energy, mood, bowel movements, sleep and even brain fog. ” Instead, focus on consuming high-fiber carbohydrates, vegetables, proteins, and fats to provide plenty of nutrients and support blood sugar balance.
You should also prioritize rehydration. “It is important to maintain adequate hydration, especially while fasting,” says Powell. “I recommend drinking half your current body weight in fluid ounces per day as a reference. So, for example, a 150-pound person would need about 75 ounces of fluid per day, not including alcohol, which is significantly dehydrating. Some people may also need more fluids than this, depending on the climate, exercise and personal needs. “
As for caffeine withdrawal, if you know in advance that you will fast and avoid caffeine, reduce your intake to prevent headaches when you start, says Mariam Eid, RDN, LDN, in Houston. By doing this, your body will have already reduced its addiction to caffeine and (hopefully) you will suffer less when you stop it.
A word on the safety of fasting
“Fasting is certainly not for everyone,” says Maeng. In particular, it is not recommended if you have diabetes or are currently pregnant or trying to conceive. If you have a history of disordered eating, underweight, or low blood pressure, fasting is strongly discouraged, she says. And more importantly: “At any time, if you feel dizzy, nauseated, irritable, or unable to concentrate or sleep, it’s best to end your fast.”
– Further reporting by Emilia Benton