Is it normal to feel shaky when fasting?

October 13, 2025 •

4 min read

The American Diabetes Association identifies shakiness as a common symptom of hypoglycemia, or low blood sugar. For many people exploring a nutrition diet that includes fasting, wondering is it normal to feel shaky when fasting? is a frequent concern that signals the body's metabolic adjustment.

Quick Summary

Shakiness during fasting is often a response to dropping blood sugar levels and changes in metabolism. It can also be caused by an electrolyte imbalance as the body loses fluids. Understanding the difference between minor adaptive discomfort and severe symptoms is critical for safe fasting practices.

Key Points

Normal Adaptation: Mild shakiness is a common and normal side effect of the body's metabolic switch from burning glucose to fat for energy during a fast.
Low Blood Sugar: The primary cause of shakiness is often a temporary dip in blood sugar (hypoglycemia) as the body depletes its glycogen stores.
Electrolyte Imbalance: Dehydration and the loss of essential minerals like sodium, potassium, and magnesium can trigger or worsen shakiness and other symptoms.
Red Flags: Severe or persistent shakiness, accompanied by confusion, heart palpitations, or vision changes, signals a need to break the fast immediately and seek medical attention.
Gradual Approach: Starting with shorter fasting windows, ensuring proper hydration and electrolyte intake, and consuming a nutrient-dense diet during eating periods can reduce discomfort.
Nutrient-Dense Diet: Eating meals rich in protein, healthy fats, and fiber during non-fasting periods helps stabilize blood sugar and prepare the body for the fasting state.

Understanding the 'Shakes' While Fasting

For many individuals new to fasting, a mild feeling of being shaky or weak is a normal part of the body's adaptation process. When you abstain from eating, your body, which is used to running on glucose from carbohydrates, must transition to an alternative fuel source: stored fat. This metabolic shift, which is central to many fasting protocols, can cause some temporary side effects. Hormones like glucagon and epinephrine are released to help regulate blood sugar levels, and epinephrine in particular can cause symptoms like shakiness and a racing heartbeat. This is a normal and often temporary part of the process, particularly during the initial stages of a fast. However, it's crucial to understand the underlying physiological reasons and distinguish normal discomfort from potential warning signs that require attention.

The role of blood sugar and hormones

During a fast, your body first uses up its readily available glucose stores, known as glycogen, from your liver and muscles. This process can take anywhere from a few hours to a day, depending on your diet and activity level. As these stores are depleted, your blood sugar level drops, which triggers the body to release hormones to begin converting stored fat into an energy source called ketones. This hormonal shift is what can cause the initial feeling of shakiness, hunger, and fatigue—a collection of symptoms often dubbed the 'keto flu'. For individuals without underlying blood sugar issues, this is a sign that the body is successfully switching metabolic gears.

The importance of electrolytes and hydration

Dehydration and electrolyte imbalance are another significant cause of shakiness and other unpleasant symptoms during fasting. When insulin levels drop during a fast, the kidneys excrete more sodium and water. This diuretic effect is a natural part of fasting, but if not managed, it can lead to a rapid depletion of vital electrolytes like sodium, potassium, and magnesium. These minerals are essential for nerve function, muscle contractions, and maintaining fluid balance, and their depletion can lead to muscle weakness, headaches, and shakiness. Sipping on water with a pinch of high-quality salt can help replenish lost electrolytes and mitigate these side effects.

Navigating Fasting and Minimizing Discomfort

To ensure a smoother fasting experience and minimize shakiness, proper preparation and listening to your body are key. This involves supporting your body with a nutrient-dense diet during your eating windows and maintaining consistent hydration with electrolytes. Starting with shorter fasts and gradually increasing their duration can also help your body adapt more slowly and comfortably.

Best practices for a stable fast:

Stay Hydrated: Drink plenty of water throughout your fast. Adding a pinch of mineral salt can help maintain electrolyte balance.
Prioritize Nutrient-Dense Foods: During your eating window, focus on whole foods rich in fiber, protein, and healthy fats. This includes leafy greens, avocados, nuts, and lean proteins, which help stabilize blood sugar.
Introduce Fasting Gradually: Don't jump into a prolonged fast immediately. Start with time-restricted eating, like the 16/8 method, to allow your body to adapt.
Consider Electrolyte Supplements: For longer fasts (over 24-48 hours) or for those who exercise while fasting, a zero-calorie electrolyte supplement may be necessary to prevent imbalances.
Listen to Your Body's Signals: Pay close attention to how you feel. While some discomfort is normal, severe or persistent symptoms are a sign to break your fast.

Normal Adaptation vs. Danger Signs: A Comparison

It's important for fasters to distinguish between the typical, mild side effects of metabolic switching and serious symptoms that indicate a more significant problem, such as true hypoglycemia or severe electrolyte collapse.


Symptom Severity	Mild (Normal Adaptation)	Severe (Danger Signs)
Shakiness	Minor, resolves after resting or with hydration.	Persistent, accompanied by confusion or extreme weakness.
Fatigue	Mild to moderate tiredness or low energy.	Inability to stay awake, repeated nodding off, extreme weakness.
Dizziness	Lightheadedness when standing up too quickly.	Severe dizziness, persistent lightheadedness, or vision loss.
Heart Rate	Mildly increased or slightly irregular heartbeat.	Heart-pounding palpitations that do not subside, significant irregular heart rate.
Cognitive Function	'Brain fog' or slight difficulty concentrating.	New confusion, slurred speech, or difficulty communicating.
Nausea	Mild, temporary nausea.	Persistent vomiting that exceeds multiple episodes in 12 hours.

When to Break Your Fast and Seek Medical Attention

While some shakiness is expected, certain symptoms are red flags. If you experience persistent dizziness, confusion, vision disturbances, or heart palpitations, you should break your fast immediately and rehydrate with fluids containing sodium. For individuals with a pre-existing health condition like diabetes, or for those taking certain medications, fasting can be dangerous and should only be undertaken with medical supervision. A blood glucose reading below 70 mg/dL (or 3.9 mmol/L) is typically considered low, and a reading below 54 mg/dL (or 3.0 mmol/L) is an emergency. If symptoms don't resolve quickly after breaking the fast, seek emergency medical care.

Conclusion

For many, mild shakiness is a transient and normal experience during fasting, indicative of the body’s metabolic shift from glucose to fat for fuel. However, this discomfort should not be ignored, as it can be exacerbated by inadequate hydration and electrolyte imbalances. By starting slow, prioritizing a nutrient-rich diet during eating periods, and judiciously using electrolytes, fasters can significantly mitigate these side effects. Always listen closely to your body. Severe or persistent symptoms are an unambiguous sign to end your fast and consult a healthcare professional. Safe and successful fasting hinges on understanding these signals and respecting your body's limits.

For more in-depth information on hypoglycemia and its management, consult authoritative sources such as the Mayo Clinic. Hypoglycemia - Symptoms and causes - Mayo Clinic.

Frequently Asked Questions

Your body shakes when you don't eat because your blood sugar levels drop. This triggers the release of stress hormones, like epinephrine, which cause shakiness as your body works to access stored fat for energy.

If you experience mild, transient shakiness, it is often a normal sign of adaptation. However, if the shakiness is severe or accompanied by other symptoms like confusion, severe dizziness, or heart palpitations, you should break your fast and seek medical advice.

Normal shakiness is mild and temporary, resolving with rest and hydration. A medical emergency is indicated by severe, persistent symptoms such as extreme weakness, persistent dizziness, visual disturbances, or heart palpitations, which require immediate attention.

Yes, dehydration and resulting electrolyte imbalances can cause shakiness, fatigue, and muscle weakness during a fast. Electrolytes like sodium and potassium are crucial for nerve and muscle function, and their depletion can cause noticeable symptoms.

For mild shakiness, drinking plenty of water is essential. To address electrolyte imbalance, you can add a pinch of mineral salt to your water or use a zero-calorie electrolyte supplement.

The 'keto flu' refers to a collection of symptoms, including shakiness, fatigue, and headaches, that can occur as your body transitions from burning glucose to ketones for energy. Shakiness is a common part of this metabolic adjustment.

You should consult a doctor if you have recurring episodes of severe shakiness, especially if you have diabetes or other health conditions. A doctor can help determine the cause and ensure your fasting plan is safe.