Does Fasting Cause Body Chills? Understanding the Metabolic Connection

October 26, 2025 •

3 min read

A significant number of people who fast report feeling a noticeable drop in body temperature and a sensation of coldness, leading many to ask, does fasting cause body chills?. The answer is yes, and it is a common physiological response as your body undergoes significant metabolic changes.

Quick Summary

Feeling cold and experiencing chills during fasting is often a result of metabolic adaptations. The body conserves energy by reducing heat production and shifting its fuel source from glucose to fat, affecting blood flow and temperature regulation.

Key Points

Metabolic Switch: Body chills often occur as your body shifts from using glucose to burning stored fat for energy.
Reduced Heat Production: The absence of digestion and metabolic heat from food contributes to a lower body temperature.
Blood Sugar Fluctuations: A drop in blood glucose levels during fasting can trigger shivering or cold sweats in some individuals.
Adjusted Blood Flow: Your body redistributes blood flow to vital organs during a fast, which can cause extremities like hands and feet to feel colder.
Temporary Effect: For most, the chilly sensation is temporary and resolves as the body becomes more efficient at using fat for fuel.
Management is Possible: Wearing warm clothing, drinking hot beverages, and light exercise can effectively manage fasting-related chills.

The Science Behind Fasting and Body Chills

When you stop eating, your body enters a new metabolic state to adapt to the absence of incoming calories, and the chills you feel are often a temporary side effect of these internal adjustments. Understanding the mechanisms can help demystify this common experience.

The Metabolic Switch: From Glucose to Ketones

During a fast, your body depletes glucose stores and switches to burning stored fat, a process called ketosis. As the body adapts to using ketones for energy, its heat-generating efficiency may temporarily decrease, leading to a reduction in thermogenesis and a colder feeling. This effect typically lessens as metabolic flexibility improves.

Reduced Thermogenesis and Digestion

Digesting and metabolizing food produces body heat through thermogenesis. When fasting, this heat production is absent, contributing to a lower overall body temperature as the digestive system rests.

Blood Sugar Fluctuations and Hypoglycemia

A drop in blood sugar can cause chills, particularly for individuals with certain health conditions or those on very strict fasting plans. Severe low blood glucose (hypoglycemia) can lead to more intense shivering and cold sweats, signaling the body's primary energy source is low. If this occurs, it may be necessary to break your fast and consult a healthcare professional.

Changes in Blood Flow Distribution

Fasting can cause the body to prioritize blood flow to vital organs, reducing circulation to extremities like hands and feet. This reallocation helps conserve energy and heat, sometimes leading to a sensation of coldness, especially in the fingers and toes.

Solutions for Managing Fasting Chills

While temporary coldness is often normal, there are ways to increase your comfort while fasting.

Tips to Stay Warm While Fasting

Drink Warm Beverages: Non-caloric warm drinks like herbal tea or warm water can help raise body temperature.
Layer Clothing: Wear insulating layers to retain body heat effectively.
Light Exercise: Gentle activities such as walking can improve circulation and generate warmth.
Warm Baths: Taking a warm shower or bath can quickly alleviate cold sensations.
Nutrient Repletion: During eating windows, consume nutrient-dense foods rich in minerals vital for metabolic health.
Add Electrolytes: Some individuals find that adding a pinch of salt to water helps with electrolyte balance, which can influence temperature regulation.

Factors Influencing Fasting Chills


Feature	Glucose-Based Metabolism	Ketone-Based Metabolism (During Fasting)
Primary Fuel Source	Carbohydrates	Stored Body Fat
Heat from Digestion	High (Thermogenesis)	Low
Core Body Temperature	Stable	May Temporarily Decrease
Blood Flow	Normal distribution	Redistributed to core/brown fat

When to Be Concerned: Underlying Issues

While feeling cold during fasting is often normal, persistent or severe sensations could indicate other issues like nutrient deficiencies affecting thyroid function. If cold sensations continue well beyond the initial adaptation or are accompanied by concerning symptoms, consult a healthcare professional to rule out other causes. A study in the Journal of Molecular Metabolism explores metabolic responses to fasting in relation to body temperature: https://pmc.ncbi.nlm.nih.gov/articles/PMC7306129/.

Conclusion

Body chills during fasting are a common and normal result of metabolic changes as the body transitions to burning fat. This leads to reduced metabolic heat, altered blood flow, and lower blood sugar. These temporary effects can be managed with simple steps like staying warm, hydrating, and ensuring proper nutrition during eating periods. While it's a sign of entering a fat-burning state, it's crucial to be mindful of your body's signals and seek medical advice if symptoms are severe or persistent.

Frequently Asked Questions

Yes, feeling cold, especially in your hands and feet, can be an indicator that your body is transitioning into ketosis, the fat-burning metabolic state.

To manage the cold, try drinking warm, non-caloric fluids like herbal tea, wearing insulating layers of clothing, and engaging in light physical activity such as walking.

Yes, a drop in blood sugar (hypoglycemia) is a potential cause of chills during fasting, as the body signals a need for more glucose.

You should consult a doctor if the cold sensations persist beyond the initial adaptation phase or are accompanied by severe symptoms like extreme weakness, confusion, or severe shakiness.

This is due to blood flow redistribution. The body conserves heat by directing blood away from the extremities and toward your core and vital organs.

Unlike traditional calorie restriction, intermittent fasting has been shown to better maintain metabolic rate, though a temporary dip in body temperature can occur as the body conserves energy and adapts.

Yes, maintaining proper electrolyte balance by adding some sodium, such as pink Himalayan salt, to your water can help with temperature regulation and overall well-being during fasting.