I published my first article on fasting back in 2005. And while I was an early author to gain traction among the burgeoning fasting community, please don’t confuse me for a fasting zealot.
From my perspective, it’s unclear whether there’s a significant benefit to fasting beyond reducing our propensity to eat too much and too often. I think it’s a great tool, but it’s not the only tool. It needs to be done correctly, with a specific goal in mind, and with the understanding that fasting is not the “bee’s knees” for everyone.
This article is for folks who do feel better practicing some form of fasting, or find it helpful for weight management. With that established, one of the most important aspects of supporting your fast will be electrolyte supplementation. Specifically, I’m here to explain why you need more sodium during a fast, how much you need, and what benefits you can expect from dialing in your sodium intake. So without further ado—let’s dive in.
The Need for Sodium While Fasting
To get one frequently asked question out of the way: No, electrolytes (including sodium) will not break a fast. Electrolytes don’t contain calories, so they don’t trigger the release of insulin or suppress fasting-related benefits. Quite the opposite, getting enough sodium is critical to feeling your best during a fast.
There are two main ways that fasting can result in sodium deficiencies: lower sodium intakes and greater sodium losses. The lowered sodium intake is self-explanatory: You’re not eating during a fast, so you’re not consuming any sodium from food. Understanding why fasting triggers greater sodium losses takes a little more science.
First, it’s long been known that fasting makes your body excrete more fluids and sodium than it typically would. Why? It depends on which researcher you ask.
One potential mechanism involves insulin — or rather, a lack thereof. When you eat foods that raise your blood sugar, insulin arrives on the scene to clean up the mess. After all, it’s best known as a blood sugar regulation hormone. But insulin also plays a lesser-known role: It helps you retain sodium. When you fast, the opposite occurs. Insulin levels drop, and you begin to lose sodium faster than Superman loses his powers in a kryptonite bubble bath. This rapid expulsion of sodium is called natriuresis.
Researchers are also exploring another mechanism for natriuresis. Rising blood sugar activates SGLT2, a sodium-glucose co-transporter in the kidneys, which increases sodium and fluid retention. But since fasting minimizes blood sugar, it inhibits SGLT2, increasing sodium and fluid excretion.
How Much Does Fasting Increase Sodium Needs?
So now that you understand why people lose more sodium during a fast, you’re probably asking: How much additional sodium do people lose due to a fast? That depends primarily on how long they’re fasting for, and on their unique physiology.
One review suggests that a person can lose anywhere from 1,100 to 5,700 mg in the first 24 hours of a fast. And in the hypothetical analysis which explored the SGLT2 mechanism, researchers predicted that a healthy person would lose (in addition to typical losses) 1,610 mg of sodium during a 24-hour fast, while a person with type 2 diabetes would lose an additional 2,553 mg (SGLT2 is more active in folks with diabetes).
Compiling learnings from a few other studies, it appears that extended fasts result in the greatest sodium losses from day 1 to day 4, and decelerate sodium losses to a low plateau by day 10:[*][*][*]
- Day 1: Expect to lose at least 1,000 additional mg sodium, and pay attention to how you feel—you may need to consume more depending on your unique physiology.
- Day 2: Expect to lose about 1,200 additional mg of sodium, increasing from there.
- Day 4: Expect to lose 1,600–3,500 additional mg of sodium, decreasing from there.
- Day 10: Sodium excretion stabilizes around 100 to 230 mg daily from this point on.
While sodium excretion (natriuresis) peaks around day 4 of a fast, most people would probably commit heinous crimes to satiate their hunger well before that. Accordingly, most people only fast intermittently between 12 and 16 hours.
Folks who fast for these shorter spurts may not incur super significant sodium losses, but if you’ve been paying attention you know they’re not in the clear… Our main source of sodium is the salt added to our food. And since you’re not eating, it’s important to prioritize consuming sodium through other means. More on that later.
Benefits of Sodium While Fasting
Taking electrolytes during a fast can prevent critical fluid and electrolyte disturbances.
In one study, 46 obese individuals consumed a daily electrolyte supplement during a six-week fast. The group lost 56 pounds on average with no severe electrolyte disturbances thanks to electrolyte supplements.
While you certainly shouldn’t perform a monstrous fast like this without medical recommendation and supervision, everyone would do well to mind their sodium intake while fasting. Here are 3 reasons why.
#1: More energy, fewer symptoms
You’ve probably heard of the keto flu—the low energy, headaches, brain fog, muscle cramps, fatigue, and malaise that arise while transitioning to a low-carb diet. Relevant here: keto flu is oftentimes a simple case of sodium deficiency.
The same holds for fasting. Like the ketogenic diet, fasting lowers insulin and causes considerable sodium loss, leading to undesirable symptoms. It also leads to overall lower sodium intakes. Replace that sodium, and you can get back to feeling your best.
#2: Better exercise performance
During exercise, you lose sodium through sweat. Combine sweat losses with fasting-related deficiencies, and you have a formula for low sodium.
This one hits close to home for me. A few short years ago I was seriously struggling on the Jiu-Jitsu mat. Not only do I fast intermittently, but I also eat a low-carb diet and sweat… A LOT. Dialing in my electrolyte intake (especially sodium) made me feel like a whole different animal.
Another quick example: A good friend recently took silver at the North America’s largest Brazilian Jiu-Jitsu tournament, the Pan Ams. He reported that increased electrolyte intake helped his energy endure like never before. I know that’s super anecdotal, so don’t take my word for it. Bump up your electrolyte intake before or during exercise and see for yourself—you’ll feel the difference when you get it right.
#3: Fewer health risks
When you chronically underconsume sodium—or lose more sodium than you replace—your body goes into sodium-retention mode. It starts:
- Pulling sodium from bone, which increases osteoporosis risk
- Releasing hormones like aldosterone, renin, angiotensin, and norepinephrine that raise blood pressure and heart disease risk
- Secreting more cortisol, increasing fat storage, bone breakdown, and muscle wasting
That’s the short list. Read more about the health risks of a low-sodium diet here.
How to Get Enough Sodium While Fasting
It’s totally normal to fall short on dietary sodium, especially if you exercise, eat a low-carb diet, eat whole foods (which are naturally low in sodium), or practice fasting. Thankfully, most nutrition apps have functions to integrate your fasting and feeding schedule. Our sodium intake calculator may be useful to establish a closer personal target range.
To hit your sodium targets, start with a dietary analysis in a nutrition-tracking app like Cronometer. The analysis will reveal your sodium intake, then you can adjust accordingly. To get enough sodium while fasting, you have a few options:
- Create your own electrolyte drink mix at home
- Take electrolyte pills
- Drink salty fluids like bone broth
- Use a well-formulated electrolyte drink mix
To avoid colossal electrolyte pills getting stuck in my throat (are these things made for horses?), and to save time measuring, mixing, and cleaning up, I prefer options 3 and 4. Bone broth is awesome, but it’s more of an occasional beverage for me. My everyday go-to is LMNT, our tasty, zero-sugar electrolyte drink mix with a science-backed ratio of sodium, potassium, and magnesium.
Remember, there’s no one-size-fits-all approach to fasting. The optimal fasting protocol remains unknown, and I’d wager that “optimal” depends entirely on you and your goals. Whatever your aim, minding your electrolytes will help you stay energized, comfortable, and happy along your health journey.