If you’re experiencing muscle cramps on keto, I sympathize. In the throes of a calf cramp, you may question why the hell you ever switched to a low-carb diet — was it to burn fat, enhance cognition, feel better? Yes, you should feel better!
Yet muscle cramps are just one symptom of the “keto flu,” a collection of symptoms including headaches, low energy, brain fog, and insomnia that tend to crop up in the early stages of low-carb dieting.
This can be particularly frustrating if you can’t pinpoint the root cause. Luckily, none of these symptoms are required for an effective keto diet! They often stem from one of three things: insufficient electrolytes (specifically sodium), dehydration, or a need for fat adaptation.
In the case of muscle cramps, it’s usually the first two. This means that, on a low-carb diet, cramps can oftentimes be avoided by upping your sodium or fluid intake. But of course, this is a multifactorial issue. Not all muscle cramps are the result of low-carb dieting. So in this article, I’ll cover a variety of common causes before providing solutions.
Muscle Cramps 101
A muscle cramp is an uncomfortable, involuntary muscle contraction. They’re nearly impossible to predict, and they can stick around for seconds, minutes, or hours. Oftentimes, neither stretching nor massage help.
These contractions (also called spasms) can occur anywhere, but most commonly affect the calves, quadriceps, feet, hands, and abdominals. According to one source, about 80% of muscle cramps occur in the calf.
Besides the keto diet, risk factors for muscle cramps include age, BMI, cardiovascular disease, kidney disease, cancer, allergies, long or intense exercise, exercising in the heat, and the use of many medications.
Let’s talk about muscle cramps during exercise now. Understanding this will help explain why people on a ketogenic diet may cramp more frequently.
Muscle Cramps from Exercise
There are two primary explanations for muscle cramps during exercise:
- Muscle fatigue
- Hydration and electrolyte balance
You’re probably familiar with hydration’s role in preventing muscle cramps. Football players, for instance, are more likely to cramp when training in the heat, likely due to heavy sweat loss. Does this mean that more water is the antidote for muscle cramps? Not so fast.
Healthy hydration isn’t just about preventing dehydration, it’s also about consuming adequate electrolytes — especially sodium, potassium, and magnesium. In one study, even severe dehydration (net water loss of 5% of body weight) didn’t increase cramping. Endurance athletes also cramp in cool climates, when sweat loss isn’t a major factor.
That’s where muscle fatigue comes in. Why might muscle fatigue cause cramping? Researchers aren’t exactly sure, but the simplified hypothesis is that muscle overuse alters the communication between the brain and the muscles, activating the nervous system and inducing spasms.
One study found that marathon runners reported all their cramps during the second half of the race, as fatigue set in. It’s not clear, however, why only a small percentage of athletes cramp up during grueling efforts.
Electrolytes and Muscle Cramps on Keto
Electrolytes are a group of electrically charged minerals with many vital functions in your body. They facilitate cellular communication via nerve impulses, maintain fluid balance, and help muscles contract and relax. Electrolyte deficiencies are undeniably linked to cramps. The main cramp-causing deficiencies are:
- Sodium deficiency
- Potassium deficiency
- Magnesium deficiency
Let’s take them one at a time.
Sodium Deficiency
Sweating increases your risk of developing muscle cramps because you lose significant sodium through sweat. Back in the 1920s, sweaty industrial workers were cramping up frequently. What solved the problem? Salt supplementation. Football players who sweat more, cramp more. The same holds for dialysis patients who aren’t given enough sodium.
But sweating isn’t the only risk factor for sodium deficiency! Those who eat a ketogenic diet tend to be sodium deficient because they excrete more sodium through urine. Why?
Restricting carbs decreases the amount of insulin in circulation, and low insulin levels decrease sodium retention. This is a simplified explanation of a complex physiological cascade, but it’ll work for the sake of this article. Not to mention, when you eat mostly whole foods (which typically don’t contain much sodium), it’s unlikely you’re getting enough salt to compensate for increased losses.
With less sodium coming in and more going out, it’s no surprise that low-carbers experience more muscle cramps than other folks.
Potassium Deficiency
Most people know that potassium helps with muscle cramps. Like sodium, potassium is a key nutrient for muscle function.
Although hypokalemia (low serum potassium) is a well-documented risk factor for cramps, more research is needed to prove that potassium supplements can prevent cramping. I believe that they may, but I’d like to see a randomized controlled trial (RCT) on this topic.
Even without perfect data from the lab, there’s no downside to hitting 3.5–5 grams of potassium per day if you have healthy kidneys. Yet 60–80% of Americans fail to even hit the adequate intake of 3.4 grams per day (in men) and 2.6 grams per day (in women). This is likely contributing to our collective blood pressure problem. And we do have solid clinical data that potassium supplementation lowers blood pressure in those with hypertension.
If you eat a ketogenic diet, it can be difficult to hit that target. Many potassium-rich foods like potatoes, fruits, and carrots are limited on keto to promote ketosis. And much like with sodium, a low-carb diet increases potassium losses through urine. Less potassium in, more potassium out, more muscle cramps.
Magnesium Deficiency
About 30% of the population is subclinically deficient in magnesium. Since magnesium is critical for muscle contraction and relaxation, this could be driving many cases of muscle cramps.
If you’re not prioritizing leafy green vegetables on keto, you’re probably not getting enough magnesium. Magnesium sits at the center of the chlorophyll molecule, so if it’s green, it’s probably rich in magnesium.
A good evidence-based target for adults 400–600 mg per day. But getting enough magnesium from diet alone isn’t easy — supplement with bioavailable forms like magnesium malate to make up the shortfall.
Blood Panel Information
By now you might be wondering if you should test for electrolyte deficiencies in the blood. Can’t you just assess sodium, potassium, and magnesium status with a blood test?
Actually, bloodwork is not a reliable way to detect dietary electrolyte deficiencies. Why? Because your body pulls these minerals from other sources (like bone) if they drop in the serum.
When sodium or potassium levels are in-range on an electrolyte panel, that just means your kidneys are working to balance fluid and electrolyte levels. It doesn’t mean that your dietary intake of electrolytes is optimal. Read this article to learn a better way of assessing electrolyte status.
How to Prevent Muscle Cramps On Keto
Muscle cramps are not inevitable on keto. Heed the following tips to prevent them.
#1: Allow recovery time
Although the data is difficult to parse, it appears muscle fatigue increases the likelihood of cramps. The more tired your muscles become during exercise, the more likely you are to cramp up. If you often cramp while exercising, consider ramping down the duration or intensity of your training. I’m not saying you should stop entirely. Just ease off and see if the cramps diminish.
You might also allow a day or two of rest between harder or longer efforts. Unless you’re training for a competition, limiting your training volume makes a lot of sense for preventing muscle cramps. It might also be prudent to rest more if you are training for a big event. Your body knows what it needs — listen to it.
#2: Drink to thirst
Most hydration websites blame dehydration for cramps. While I can see how dehydration could result in cramping, some evidence indicates that even serious dehydration doesn’t increase cramp frequency in athletes.
The important takeaway is, again, to listen to your body. Drinking to thirst — a finely tuned mechanism honed over millions of years — makes it easy to avoid both dehydration or overhydration. And yes, overhydration can be a serious issue.
Chugging water with blatant disregard for thirst can launch you straight past sodium deficiency into a dangerous condition of low blood sodium called hyponatremia. Overhydration is the number one cause of exercise-associated hyponatremia among athletes.
Since keto acolytes already deal with increased sodium losses via urine, it’s especially important these folks heed their thirst appropriately.
#3: Take electrolytes
The most important tip for preventing cramps on keto? Dial in your electrolyte intake. This means consuming enough sodium, potassium, and magnesium to reach these science-backed targets:
Prioritize dietary sources first, and then supplement any shortfall accordingly. On a keto diet, this means eating lots of leafy greens for potassium and magnesium. Sodium can come from pickles, olives, and salting your food. (4–6 grams of sodium is about 2–3 teaspoons of salt.)
You can also salt your water. To make your electrolyte water more palatable, add a squeeze of lemon juice or use a no-sugar electrolyte drink mix like LMNT. With LMNT, you’ll also get some extra potassium and magnesium to help you avoid keto muscle cramps.
Before we sign off, remember this sentence: Drink to thirst, get enough electrolytes, and take breaks to avoid overtraining. Your muscles will thank you.
