Is It Normal to Get a Headache When Intermittent Fasting?

Published December 23, 2019 | Published by Daisy Cabral

There are dozens if not hundreds of different methods out there aimed at helping people lose weight. They run the gamut from extreme exercise to extreme calorie cutting to a mixture of both. There are low carb diets, high carb diets, all-protein diets, and anything else you can think of. 

One such weight loss method is intermittent fasting. Intermittent fasting, or IF, is a very popular diet these days for a few reasons. One of the primary reasons, of course, is that it doesn't care what you're eating, only when you're eating. You can still eat all of your favorite foods, you just need to mix it up with periods of fasting.

Fasting, in case you're not sure, is simply the act of eating nothing. Throughout history it has been used for anything from weight loss to honoring the passing of a prominent member of the community to hunger protests. 

Fasting takes advantage of a part of your body's evolution. As a hunter-gatherer society, you may not have been able to find food readily available whenever you're hungry. If you've ever gone hungry for a while, you've likely noticed that you have hunger pangs for a while, and then they pass.

This passing of the hunger pangs exists to remove distractions that might otherwise make you miss a hunt. When you're seeking food, and in particular when the food you're seeking can escape, you want as few interruptions as possible.

Fasting also converts your body from using up energy in what you're digesting – which is nothing, because you aren't eating – to burning stored fat for energy. This process, known as ketosis, is the foundation of many low-carb diets as well. 

Fat storage in the body, of course, came about for exactly this process. When your body has more energy – calories – than it can burn through the activity you're doing, it stores the excess as fat for later. 

Think of it like a laptop battery. As long as your laptop is plugged in (or your body is eating) you can operate indefinitely. When you deprive the laptop (your body) of incoming energy by unplugging it (or cutting off food), it has a battery storing energy (fat cells) that it can use to operate for a while before needing to be plugged back in (or eat more food).

Intermittent fasting requires you to eat nothing for a period of time. Some plans have you fast for 16 hours each day, while others ramp it up to 24 hours, twice a week.

In order to lose weight, you need to take in fewer calories than you're burning. If you consume more calories than you burn, you store excess as fat and gain weight. If you burn exactly as much as you take in, you neither gain nor lose weight. If you burn more than you take in, you lose weight. It's just simple math.

It takes roughly a caloric deficit of 3,500 calories to lose one pound. Spread throughout the week, this means a deficit of 500 calories per day. Considering that the average human consumes between 2,000 and 4,000 calories per day – depending on diet, lifestyle, and so on – intermittent fasting can cut that amount of calories from your diet in one day out of the week.

Different Methods for Intermittent Fasting

There are a few different methods you can use for IF, and it's worth checking out each of them to see which has the fewest side effects on your body. Remember that IF can be hard on the body, at least until you get used to it.

The 16/8 Method divides the day up into hours. 8 hours of the day, starting with your breakfast, is the time you have available to eat. If you want to eat something, but it's outside of those hours, you're out of luck. Some people start this with breakfast and end with dinner roughly seven hours later, while others skip breakfast and just eat lunch and dinner. Try to choose a set of hours you can comply with regularly every day, such as 1pm to 9pm when you're guaranteed to be awake every day.

The weekly fasting method or the Eat Stop Eat method involves picking two days through the week that are not consecutive (such as Tuesday and Friday) and fasting those days. You eat nothing between dinner of the previous day and dinner of that day, for 24 hours of non-consumption.

The 5:2 Diet method picks two days of the week to dramatically limit, but not entirely cut, consumption. For example, you might pick Monday and Thursday. On those days, you limit yourself to only 500-600 calories of consumption. Other days throughout the week you eat normally.

Part of the key of any IF method is to not compensate as well. Compensation means eating larger meals on the days you're free to eat, to make up for the calories you didn't eat on other days. Since your goal is to reduce overall weekly caloric consumption, making up for cutting is just putting you back at square one.

Side Effects of Intermittent Fasting

Now let's get to the real reason you came to this post: the side effects. Since the title of this post is about headaches, let's start there. Are headaches a natural side effect of IF, or are they something you should be concerned about?

There are actually two kinds of headaches: primary and secondary. Primary headaches are headaches like tension or migraines. They're just headaches that happen with no known underlying cause or disorder. Secondary headaches have a cause, which can be anything from a brain tumor to an exposure to a toxic substance, to a break in homeostasis.

Homeostasis is the body's natural balance keeping everything in check. A disruption in blood sugar, blood pressure, or hydration levels can all throw your body out of balance.

Secondary headaches are a common side effect of many things. Unfortunately, headaches are also a poor diagnostic. When you get a headache, it could be caused by anything from tension in your neck and shoulders to a lack of water to a lack of sugar in your blood. That said, if the only thing you've changed in your life is that you've started intermittent fasting, that's a pretty good indicator that the disruption of homeostasis is causing the headache.

A headache simply means something is out of balance, so yes, a headache is a natural part of intermittent fasting. Not everyone gets them, but many people do. Sometimes they're light and ignorable, and sometimes they can be close to migraines. 

Headaches are not generally cause for concern with intermittent fasting, with a few exceptions.

  • If you're generally very sensitive to headaches, IF headaches can make it hard to function on the days where you're fasting. You might consider a less extreme version of IF to see if they get lighter or go away.
  • IF headaches can also make it difficult to maintain the willpower necessary to keep up the fasting plan. If you can't keep it up, you won't lose weight, so this is important to consider.
  • If your IF headaches are extreme, you might consider talking to a doctor. You may have an underlying issue, such as pre-diabetes, that needs to be addressed. 

Additionally, if you're looking into trying intermittent fasting, you want to make sure you aren't susceptible to negative side effects. If you're already somewhat malnourished or are underweight, IF can be dangerous for your health. Additionally, IF can be detrimental if you're trying to conceive or if you're pregnant. Never deprive your body of nutrients when you're nourishing a child.

What Causes Intermittent Fasting Headaches?

While yes, IF can cause headaches, why does it cause them? What mechanism in the body is being disrupted? Obviously, you're not eating food, and the lack of caloric intake is a change. However, many people fast on a regular basis and don't experience headaches. So why are you?

One of the most well-known and well-understood causes is hypoglycemia. When you eat food, a large part of that food is some form of sugar, including carbohydrates. When you fast, you cut out your sugar intake, which causes a lowered blood sugar. Low blood sugar is hypoglycemia (literally "under-sugared"). Your body needs a certain level of blood sugar to function properly. This has been well-studied as part of religious fasting for decades.

There may be other underlying causes for headaches during IF, but blood sugar is by far the most common.

How to Handle Intermittent Fasting Headaches

So if you do get headaches when you're trying out IF, what can you do to ease the pain or eliminate the headaches?

Before trying anything else, make certain you're drinking enough water. Dehydration is one of the most prominent causes of headaches, both in general and with intermittent fasting. Sometimes, making sure you're drinking plenty of water will help minimize or eliminate the headaches entirely. That said, there are other options as well.

First, you can simply try to tough it out and stick with it. Intermittent fasting has been shown to reduce insulin resistance, a symptom of pre-diabetes or diabetes. Once you've been fasting for a few weeks or months, your body may adjust and be able to better use the sugar it already has, which will reduce or eliminate the headaches. Yes, it will suck for a while before you get used to it, but you can get used to it.

Second, you can try to manage the pain with medications. You have to be very careful with this. With nothing in your stomach, pain medications can irritate the stomach lining. Abuse of such medications can even lead to disorders such as ulcers. There are some pain options that aren't taken orally, so consult with your doctor if the headaches don't go away.

Third, there's always the not-quite-fasting options. Adjusting your choice of intermittent fasting plan to one where you cut down your active eating hours each day, rather than one where you cut out eating entirely on full days, can ensure a stable level of sugar and water in your blood. It might mean you're not on quite as extreme a path to weight loss, but it's better to lose weight slowly but comfortably than it is to suffer through it and be more likely to quit or relapse.

You should also try to fast on days where you're not likely to be stressed. Stress hormones can induce headaches or make existing headaches worse. They can also mean you're irritable and have a shorter temper than normal. This is why many people choose to fast on their days off rather than in the middle of the week, where they have to deal with the stresses of work or coworkers. Minimizing sources of stress can help make fasting more effective and more comfortable.

Another thing to consider is that not all fasting is absolute. Some fasting plans allow you to consume things like juices as well as water. These are a way to provide some sugar to your body to help prevent things like headaches. 

There are no hard and fast rules with intermittent fasting, at least not for weight loss. If you're fasting for orthodox Judaism, Ramadan, or another religious cause, that's a different story. Even so, it's best to do what's best for your body, so adapt your fasting to your own needs.

Your Turn

Have you tried out intermittent fasting before? Tell us your story! In the comments below, tells us details like how often and how extreme your fasting was or is, how quickly and how much weight you've lost, and what side effects you've had. Especially if you've had headaches, let us know how you've dealt with them. Did they go away, or did you have to change your habits? Help us help you out!

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