Feeling Cold While Fasting

Why It Happens

Feeling cold during a fast is common and has a straightforward explanation. Your body generates heat as a byproduct of digesting food — this is called the thermic effect of food. When you are not eating, this heat production decreases. Additionally, as insulin falls and the body shifts to fat metabolism, thyroid hormone activity can temporarily shift, which affects body temperature regulation.

Is It a Problem?

For most people, feeling slightly cooler than usual during a fast is not a medical concern — it is a normal metabolic adaptation. It becomes relevant only if it is extreme or accompanied by other symptoms like shaking, confusion, or inability to warm up.

Practical Solutions

Warm beverages help significantly — hot black coffee, plain herbal tea, or warm water with a pinch of salt. Keeping your body moving with light activity raises core temperature. Layering clothing is obvious but effective. Most people find this symptom diminishes after the first 2–3 weeks as metabolic adaptation progresses.

A Note on Thyroid Health

Prolonged caloric restriction can affect thyroid function over time. This is more relevant to extended fasting (multiple days) than typical intermittent fasting. If you are doing daily 16–20 hour fasts and consistently feel very cold, fatigued, and have other symptoms of low thyroid function, it is worth getting thyroid labs checked.

See also

• Electrolytes Explained
• What to Expect Your First Week of Fasting