Does Fasting Lower Body Temperature? An In-Depth Nutritional Look

October 25, 2025 •

3 min read

Feeling chilly during a fast is a common experience, with studies confirming that metabolic rate and body temperature can decrease during periods of reduced food intake as an energy-saving strategy. This natural physiological response is part of the body's adaptive thermogenesis to conserve energy when nutrients are scarce. The answer to "does fasting lower body temperature?" is yes, and understanding the mechanisms behind it can help you navigate this common side effect.

Quick Summary

Fasting can cause a temporary reduction in body temperature as the body shifts its metabolic state to conserve energy. This is primarily due to decreased thermogenesis from digestion, a shift toward fat-burning, and changes in circulation that prioritize core heat. As metabolic flexibility improves, this sensation often subsides.

Key Points

Metabolic slowdown: The body lowers its metabolic rate during fasting to conserve energy, resulting in less internal heat production.
Digestive pause: The heat generated from digesting food, known as thermogenesis, ceases during fasting, contributing to a cooler feeling.
Ketosis transition: As the body shifts from burning glucose to fat for fuel (ketosis), initial metabolic adaptations can temporarily reduce heat generation at the cellular level.
Blood flow changes: Circulation is redirected from extremities like hands and feet to the core, which helps maintain vital organ temperature but can cause limbs to feel cold.
Temporary adaptation: For most, feeling cold is a temporary side effect that resolves as the body becomes more efficient at burning fat and adapts to the new metabolic state.

The Core Mechanisms of Fasting-Induced Temperature Changes

When you stop eating, your body's energy landscape fundamentally changes. Without a constant influx of glucose from food, your body initiates a series of metabolic adaptations to conserve energy and find alternative fuel sources. This cascade of events has a direct impact on your internal thermostat.

Reduced Thermogenesis from Digestion

One reason for feeling cold is the cessation of diet-induced thermogenesis (DIT). Digesting and absorbing food requires significant energy and generates heat, and when fasting, this process stops, reducing heat production.

The Metabolic Switch to Ketosis

As fasting continues, the body depletes glycogen and starts burning fat for fuel, entering ketosis. This shift can temporarily reduce thermogenesis as the body adapts to using ketones for energy.

Blood Flow Redistribution

During fasting, blood flow may be redirected from extremities to core organs, helping maintain their warmth but causing hands and feet to feel cold.

Hormonal and Neural Adjustments

Fasting also impacts hormones and neural pathways that regulate temperature. Insulin levels drop, contributing to a metabolic slowdown, and the brain's temperature control center is involved in adapting to nutrient scarcity.

Comparison: Fed State vs. Fasted State Thermoregulation

Understanding temperature management in both states clarifies the changes during fasting. The table below highlights key differences:


Feature	Fed State	Fasted State (Initial Adaptation)
Metabolic Fuel	Primarily glucose from food	Primarily fat (ketones) from fat stores
Thermogenesis (Heat Production)	High due to digestion and metabolic activity	Low due to resting digestive system and metabolic conservation
Insulin Levels	High to manage blood sugar	Low to allow fat breakdown
Blood Flow	Normalized distribution to digestive system and extremities	Redistributed from extremities toward core
Energy Strategy	Energy expenditure and storage	Energy conservation and mobilization of reserves
Sensation	Normal or warm due to digestion	Feeling of cold, especially in hands and feet

Strategies to Mitigate Feeling Cold While Fasting

While temporary coldness during early fasting is normal, these strategies can help:

Stay active: Gentle movement can improve circulation and increase body heat.
Stay hydrated: Drinking warm, fasting-friendly liquids like herbal tea can help combat cold sensations.
Wear layers: Dressing warmly is a simple way to conserve body heat.
Optimize nutrient intake: During eating periods, consume nutrient-rich foods to support thermoregulation with minerals like zinc, selenium, and magnesium.
Take a warm bath: A warm bath or shower can quickly raise body temperature.

The Long-Term Perspective

The cold sensation often subsides as the body becomes more efficient at using fat for fuel. If it persists, consult a healthcare professional to rule out other issues like thyroid problems. Research on diet, metabolism, and thermoregulation is ongoing, such as in this MDPI study on metabolic and circulatory changes during prolonged fasting: Body Temperature, Metabolic, and Circulatory Changes After 8 Days of Water-Only Fasting in Healthy Middle-Aged Men.

Conclusion

Feeling cold during fasting is a normal physiological response for most healthy individuals, reflecting the body's adaptation to conserve energy. Understanding the metabolic and circulatory changes and using simple warming strategies can make this experience more comfortable. This temporary temperature drop is part of the body's move towards metabolic flexibility and efficiency.

Frequently Asked Questions

Yes, it is a common and normal physiological response, especially in the early stages of adapting to intermittent fasting. It is typically related to your body shifting from burning glucose to using stored fat for energy.

Your body is designed to prioritize the warmth of your vital organs. During a fast, blood flow is often redirected away from your extremities, such as your hands and feet, to keep your core temperature stable.

Yes, dropping blood sugar levels can affect body temperature regulation and cause a sensation of feeling cold. This is more common with more restrictive or prolonged fasting.

Feeling cold can indicate that your body is beginning to enter ketosis. As your metabolism shifts to utilizing fat for energy, a temporary drop in body temperature can occur as part of the metabolic change.

You can stay warm by wearing warm layers of clothing, drinking hot beverages like herbal tea, and engaging in light physical activity such as walking to improve circulation.

Yes, deficiencies in key minerals like iodine, selenium, and zinc can impair thyroid function, which is crucial for regulating body temperature. Ensuring nutrient-dense meals during your eating window can help.

Feeling cold is often a temporary side effect of metabolic adaptation. However, if the cold sensations are severe or persist well beyond the initial adaptation period, it is recommended to consult a healthcare professional to rule out any underlying issues.