Fasting headaches: Causes and remedies

If you have a headache while fasting, specifically, it could be more than your run-of-the-mill noggin throbbin’.

The fix might be simple. For instance, it might be a matter of hydrating properly with fluids and electrolytes.

But the fix could also require more involvement. A fasting headache could be your brain crying out for fuel, and fixing that problem often requires a dietary change.

Today I’ll cover the most common causes of fasting headaches, along with each of their remedies. But first I want to lay some philosophical groundwork around fasting and suffering. In short… you don’t have to. “Really?” Yes, really. Let me explain.

Fasting and Discomfort

A fasting headache means something is wrong, but people often overlook the simplest solution.

The simplest solution is to break the fast. Ease up on the regimen. Cut yourself some slack.

A lot of folks are super stoic about fasting. They power through any discomfort—including raging headaches—to get to the finish line.

I agree there’s a place in life for stoicism. All of us have (or will) hit hard times, and the stoic learns to accept what she can’t control.

But there is an element of control with fasting. You control your regimen. If you’re doing everything right and still feel lousy, maybe you’re fasting too aggressively.

Fasting is a powerful stressor, and not all humans react favorably to long periods of nutrient deprivation. Some people feel best at one meal a day, others at two, and others still at three.

Me? I feel my best fasting around 14 to 16 hours per day. But I also eat a keto diet, and eating keto makes fasting easier. I’ll riff more on this later.

But I don’t feel the need to push my fasts any longer. For me, the cons—lower energy, hunger, sleep loss, impaired fasted training—outweigh any potential pros.

Don’t I want to activate autophagy, the cellular recycling program everyone’s raving about these days? Well, it sounds like a nice benefit, but the truth is, we don’t have a reliable way to measure autophagy in humans yet.

How long must one fast to induce meaningful autophagy? A day? Three days? A week? Nobody knows. And anyone who says they do is either confused or dishonest.

Besides, I’m probably getting a decent hit of autophagy from exercise and low-carb dieting. I’m not sure fasting would be additive. Maybe it is. But did you know coffee enhances autophagy?! Approach this stuff any way you like, but it feels important to recognize that far too many Instagram gurus paint fasting as the only route to autophagy. It’s not.

To summarize this rant: I don’t think fasting is worth a ton of discomfort. (And this discomfort can manifest even if you’re doing everything right!). Better to take it easy, take it slow, and not get too aggressive with fasting—especially without clinical supervision.

Let’s bring this back to headaches. If you have a headache while fasting, the first thing to ask yourself is...

Is Fasting Causing Your Headaches?

We’ve all had the continuous pain in the head known as a headache. And many people have also experienced a more severe headache called a migraine, considered the top cause of disability in those under 50.

Both headaches and migraines have a long list of potential causes. These causes include:

  • Sleep deprivation
  • Medication or supplement usage
  • Low blood sugar
  • Brain inflammation from head trauma, infection, or another condition
  • Electrolyte imbalances
  • Dehydration
  • Stress
  • And many others

Some of these causes—like electrolyte imbalances and low blood sugar—can be directly linked to fasting. I’ll cover this in the next section.

But other causes aren’t so direct. For instance, a 2017 systematic review found the most powerful predictors of chronic headaches to be depression, anxiety, medication overuse, poor sleep, and high stress.

Start with these factors when addressing a headache problem. And if the headaches always arise when you fast, keep reading for possible causes.

Fasting Headaches: Causes and Remedies

If your head is pounding during a fast, it makes the experience about as fun as doing your taxes in a jungle hut without air conditioning. To address the problem, look to these causes first.

Cause #1: Low sodium

The medical community has known for decades that fasting provokes increased sodium loss through urine. This is called “the natriuresis of fasting”, and it’s why sodium levels are closely monitored during therapeutic fasts.

If sodium isn’t replaced, the patient may develop low serum sodium, also called hyponatremia. The symptoms of hyponatremia include headache, fatigue, weakness, and brain fog.

Those practicing intermittent fasting probably won’t develop clinical hyponatremia, but even a mild sodium imbalance can cause headaches.

This imbalance is perpetuated by advice to “drink more water” during a fast to prevent dehydration. Unfortunately, drinking plain water dilutes blood sodium levels and can make the problem worse.

And so, you have at least three forces sapping sodium status during a fast:

  1. The natriuresis of fasting
  2. Overhydration with plain water
  3. A lack of incoming sodium

The remedy? Consume sodium during a fast. Get your sodium by drinking bone broth, adding salt to lemon water, or using a salty electrolyte drink mix like LMNT.

Cause #2: Dehydration

Along with causing natriuresis (sodium loss), fasting also causes diuresis. This means you lose both sodium AND fluids more rapidly during a fast.

If fluids aren’t replaced, dehydration (net water loss) can result. And headaches are a hallmark dehydration symptom.

But here’s the thing. Dehydration is rare in healthy people.

Why? Because most people have well-calibrated thirst mechanisms. When they start to lose fluids, they drink something.

Because of this, I believe dehydration is an unlikely cause of fasting headaches. And like I mentioned earlier, drinking beyond thirst can exacerbate electrolyte disturbances.

The remedy? Drink electrolyte water thirst to stay hydrated during a fast. 

Cause #3: Brain fuel issues

When you deprive yourself of nutrients, your brain doesn’t take a break. It keeps burning fuel.

A lot of fuel. Your brain is only 2% of your weight yet accounts for about 25% of your total energy usage.

On a carb-containing diet, glucose is your primary brain fuel. Carbs digest to glucose and glucose powers neurons.

When you fast, your incoming supply of glucose goes to nil. Your brain can also run on an alternate fuel source (ketones), but this switch doesn’t happen immediately.

And so with glucose low and the brain transitioning to ketones, headaches, brain fog, and fatigue can result. This can also happen on the keto diet. It’s called keto flu.

The takeaway is: if you’re not on a low-carb or keto diet, any fast longer than 13 or 14 hours may be uncomfortable for your brain. You won’t be sufficiently keto-adapted to handle the drop in blood glucose.

The remedy? There are two possible remedies:

  1. Eat a low-carb or keto diet so your brain can run smoothly on ketones during a fast.
  2. Back off to an easier fast. (No shame in that).

Cause #4: Poor sleep and stress

Both sleep deprivation and stress have been linked to chronic headaches. Unfortunately, fasting can underlie these problems.

There’s a reason why many folks have sleep issues while fasting. During a fast, your body upregulates stimulating chemicals like epinephrine, norepinephrine, and orexin-A that keep you alert like a hungry chipmunk.

This biological system is no accident. Animals need that boost of alertness so they can find food when they’re starving. Starvation is the only time animals voluntarily miss sleep.

This is another reason I’m not crazy about extended fasting. By losing your precious sleep, you may be doing more harm than good.

The sleep deprivation caused by fasting can also increase stress levels—another potential cause of headaches.

Fasting itself is a stressor. It elevates fight-or-flight hormones like epinephrine, norepinephrine, and cortisol. If you have a mellow constitution and a fairly low-stress life, the stress of fasting may be just what you need. If your life is a chaotic jumble, fasting could be a disaster.

Ever wondered why you feel more relaxed after eating? It’s your body breathing a sigh of relief. Ah, nutrition.

The remedy? If you’re sleeping poorly, stressed, and your head hurts while fasting, it’s time to ease up on the protocol and extend your feeding window. For beginners, I recommend starting with a 12 or 13 hour fast and working your way up—one hour at a time—as comfort and schedule permit.

How To Deal With Fasting Headaches

Struggling with fasting headaches? Follow these three steps:

  • Dial in your hydration. Drink electrolyte water to thirst to prevent electrolyte imbalances and dehydration while fasting. One or two sticks of LMNT should do the trick.
  • Consider other causes. Are you sure the cause of your headache is fasting-related? Could it be a medication or supplement instead? Take a break from your fasting protocol and see if the headaches persist. If they do, look elsewhere for answers.
  • Try a low-carb diet. Going keto helps your brain adapt to using ketones for energy. This should reduce the likelihood of headaches occurring. Just keep in mind that low-carb diets cause you to pee out even more sodium, and it needs to be replaced or headaches could worsen.

If these steps aren’t helping, I urge you to listen to your body. A headache means something is wrong. If eating more frequently rights that wrong, eat more frequently.

Maybe your optimal fast is 12 or 13 hours, not 24 or 36 hours. There’s nothing wrong with that. Let your body be your guide and your fasting headaches will soon be a thing of the past.