Understanding Nutrition and Diet: What Causes Cramps When Dieting?

October 18, 2025 •

4 min read

According to reports, muscle cramps are a common side effect for many people who undertake restrictive diets. If you've ever wondered what causes cramps when dieting, the primary culprits often include issues with fluid and electrolyte balance that directly impact muscle function.

Quick Summary

Muscle cramps during dieting are most often caused by dehydration and imbalances in critical electrolytes, including sodium, potassium, and magnesium. These issues frequently arise with low-carbohydrate and very low-calorie eating plans, as well as with intense exercise.

Key Points

Electrolyte Imbalance Is Key: The most common reason for dieting cramps is a deficiency in electrolytes like sodium, potassium, and magnesium, which are crucial for muscle function.
Dehydration Is a Major Factor: Many restrictive diets, especially low-carb ones, cause increased urination and fluid loss, leading to dehydration and cramping.
Low-Carb Diets Impact Electrolytes: Ketogenic diets can cause rapid depletion of electrolytes and fluids as the body adapts, often resulting in "keto flu" symptoms like cramps.
Replenish With Mineral-Rich Foods: Incorporate foods high in potassium (avocados), magnesium (leafy greens), and sodium (broth) to balance electrolyte levels and prevent spasms.
Exercise and Rest Moderately: Intense workouts can worsen cramping when combined with dieting. Prioritize hydration, stretching, and adequate rest to support muscle recovery.

The Primary Culprits: Dehydration and Electrolyte Imbalance

When you begin a new diet, especially one that restricts carbohydrates or calories, your body undergoes significant metabolic changes. These shifts often alter fluid levels and deplete essential minerals known as electrolytes, which are vital for proper muscle contraction and nerve signaling.

The Link Between Dehydration and Cramps

Dehydration is a leading cause of muscle cramps, and many diets inadvertently increase your risk. When you reduce carbohydrate intake, your body burns through its glycogen stores for energy. Glycogen is stored with water, so as it's used, a significant amount of water is released and flushed from the body through urination. This rapid fluid loss, if not adequately replaced, can lead to dehydration and a higher likelihood of muscle cramping.

Electrolyte Imbalance

Electrolytes such as sodium, potassium, and magnesium are critical for regulating muscle and nerve function. When you lose fluids during dieting, you also lose these important minerals. This imbalance disrupts the electrical signals that tell your muscles when to contract and relax, leading to involuntary and painful spasms.

Sodium: Lost through increased urination and sweat, low sodium (hyponatremia) can directly cause cramps by affecting fluid balance and nerve impulses.
Potassium: Works closely with sodium to regulate fluid and electrical signals. Restrictive diets, especially those low in fruits and vegetables, can quickly lead to potassium deficiency (hypokalemia).
Magnesium: Often called the "relaxation mineral," magnesium is crucial for muscles to relax after contracting. Deficiency allows for excessive calcium buildup in muscle cells, causing persistent tension and cramps.

How Specific Diets Trigger Cramps

Certain popular eating plans carry a higher risk of causing cramps due to their specific effects on the body.

Low-Carbohydrate and Ketogenic Diets

The initial phase of a ketogenic diet, known as the "keto flu," is notorious for causing symptoms like fatigue, headaches, and muscle cramps. As the body switches from burning glucose to fat for fuel, insulin levels drop, triggering the kidneys to excrete more sodium and, consequently, more water. This rapid electrolyte and fluid loss is a prime cause of cramping for many people starting keto.

Fasting and Very Low-Calorie Diets

Intermittent fasting or very low-calorie diets limit the window or amount of food consumed, which can result in insufficient intake of essential minerals and fluids. Without a consistent supply of nutrients, the body's electrolyte stores can become depleted, triggering muscle spasms and other symptoms.

Restrictive Diets and Nutrient Deficiencies

Overly restrictive diets that eliminate entire food groups can lead to deficiencies in other vital nutrients. Calcium, which works alongside magnesium in muscle function, and certain B vitamins, important for nerve signaling, can also be low in poorly planned diets. A lack of vitamin D, which aids in calcium absorption, can also contribute.

Lifestyle Factors that Exacerbate Cramps

Beyond what you eat, certain habits can increase your susceptibility to cramps while dieting.

Overtraining and Muscle Fatigue

Intense exercise can deplete glycogen stores, fluids, and electrolytes, especially if you sweat heavily. When combined with a restrictive diet, this increased loss and reduced replenishment can push your muscles into a state of fatigue and make them more prone to spasming. It is crucial to balance your training intensity with your dietary changes to prevent overexertion.

Comparison of Diets and Cramp Risk


Dietary Approach	Primary Cramp-Related Risk	Key Nutrients Impacted	Prevention Strategy
Balanced Diet	Low risk; typically associated with intense exercise or poor hydration.	Generally well-balanced, but needs attention during heavy sweating.	Consistent hydration, varied food intake.
Low-Carb / Keto Diet	High initial risk due to rapid water and electrolyte loss (keto flu).	Sodium, Potassium, Magnesium.	Active electrolyte replenishment via salt, bone broth, and supplements.
Fasting / VLCD	High risk due to limited opportunity for nutrient intake.	Sodium, Potassium, Magnesium, Calcium.	Focus on hydrating with electrolyte water during fasting windows, consume nutrient-dense meals.
Restrictive Diet	Moderate to High risk from excluding nutrient-rich food groups.	Dependent on exclusion; e.g., Dairy-free risks Calcium deficiency.	Careful planning to ensure all nutritional gaps are filled with alternatives or supplements.

Prevention and Management Strategies

Preventing and managing cramps while dieting involves a combination of smart dietary choices, hydration, and mindful exercise.

Stay Hydrated: Drink plenty of water throughout the day. For intense exercise or very low-carb diets, consider electrolyte-fortified water or sipping on bone broth to replace lost salts.
Replenish Electrolytes through Diet: Incorporate electrolyte-rich foods into your meals. Good sources include leafy greens (magnesium), avocados (potassium), nuts (magnesium), and salting your food to taste (sodium).
Don't Overdo Exercise: Be mindful of your training intensity and listen to your body. Consider gentle activities like walking or stretching, especially when first starting a new diet plan.
Stretch and Massage: Gently stretching the cramped muscle can provide immediate relief. A warm compress or a light massage can also help relax tight muscles.
Consider Supplements: If diet is not enough, a supplement for magnesium, potassium, or a multi-mineral complex may be necessary. Always consult with a doctor or registered dietitian before starting any new supplement regimen.
Introduce Changes Gradually: If you are transitioning to a low-carb diet, do so gradually to allow your body to adapt without shocking the system.

Conclusion

Understanding what causes cramps when dieting is the first step toward effective prevention and management. For most people, these painful spasms are a temporary side effect of shifting fluid and electrolyte levels, particularly with low-carb or fasting protocols. By prioritizing hydration, actively replenishing key minerals, and listening to your body's signals, you can maintain your health and comfort while successfully pursuing your dietary goals. Persistent or severe cramping could signal an underlying issue, and you should consult a healthcare professional for a proper evaluation. Further information on electrolyte function and muscle health can be found via the Cleveland Clinic.

Frequently Asked Questions

While a deficiency in any key electrolyte can cause cramps, magnesium is often specifically noted for its role in muscle relaxation. Low magnesium can lead to over-excitability and painful muscle spasms.

Yes, fasting can cause muscle cramps. Limiting your food intake over a period of time, such as with intermittent fasting, can deplete your body's stores of minerals and electrolytes, triggering muscle spasms.

To get enough potassium while on a low-carb diet, focus on keto-friendly, potassium-rich foods like avocados, spinach, beet greens, and mushrooms. Consuming bone broth and salting your food can also help.

Yes, staying consistently hydrated is crucial. However, on some diets, especially low-carb, you also need to replenish lost electrolytes along with the water to effectively prevent cramps.

Yes, night-time leg cramps are a common complaint for people on restrictive diets. Magnesium levels can naturally fluctuate and are often lowest at night, making cramps more likely.

Over-the-counter pain relievers like ibuprofen or acetaminophen can help manage residual soreness after a cramp has subsided but do not directly address the electrolyte imbalance or dehydration causing the cramp.

If muscle cramps are severe, persistent, or accompanied by other symptoms like extreme fatigue, numbness, or an irregular heartbeat, you should see a doctor to rule out more serious medical conditions.