Do You Get Cold When Fasting? | Why It Happens And Fixes

Some people breeze through a fast. Others end up in a hoodie, hands like ice. If that’s you, you’re not weak and you’re not “doing it wrong.” A fast changes what you burn for fuel, how you hold heat, and how your body prioritizes energy.

Below you’ll get the plain reasons fasting can make you feel cold, what’s normal, what’s not, and how to stay comfortable without wrecking the point of fasting.

Why Fasting Can Make You Feel Cold

Your body keeps core temperature in a tight range. When food stops coming in, it leans on stored fuel and trims “extra” energy spending. That can change heat production and heat loss at the skin.

Less Meal-Related Heat

Eating creates heat. Digesting, absorbing, and storing nutrients costs energy, and some of that energy shows up as warmth. When you skip meals, that heat source drops, so you may feel cooler in the same room.

Glycogen Runs Down Early

In the first stretch of a fast, your liver and muscles use glycogen (stored carbohydrate). As glycogen falls, some people feel flatter and colder, especially if they were used to frequent meals or high-carb days.

Skin Blood Flow Narrows To Hold Heat

To conserve heat, your body can narrow blood vessels near the skin. That reduces heat loss from the surface but makes fingers and toes feel colder. Physiology references on cold exposure describe this drop in peripheral blood flow as a normal heat-saving response. Physiology of cold exposure explains how this response reduces heat transfer from the core to the skin.

A Bigger Calorie Gap Can Add To The Chill

Many fasting plans also reduce total weekly calories. If the deficit is steep for days in a row, you may feel cold more often. That’s your body trying to spend less energy.

Do You Get Cold When Fasting?

Yes, many people do, especially during the first week, on longer fasts, or when fasting stacks with low sleep, low carbs, or hard training. For most, it’s a nuisance that fades when you warm up or when you eat.

Still, a cold feeling can overlap with low blood sugar, dehydration, anemia, or thyroid issues. The pattern and the extra symptoms matter.

Feeling Cold While Fasting With Real-World Triggers

These factors often decide who gets cold and when it hits.

Low Body Fat Or Small Frame

Body fat acts like insulation. People who are lean often lose heat faster, especially from hands and feet.

Not Drinking Enough Water

Fasting can increase fluid loss early, since insulin drops and you may pee more. Low fluid can leave you sluggish and chilled. Warm fluids can help, even if they’re calorie-free.

Low Sodium From Sweat Or Frequent Bathroom Trips

If you sweat from workouts or you’re peeing a lot, sodium can drop. That can leave you feeling weak, lightheaded, and cold. If you have blood pressure or kidney issues, get clinician guidance before raising sodium.

Too Much Caffeine On An Empty Stomach

Some people get sweaty, then cold, with shaky hands. If that’s you, lower the dose or switch to tea.

Short Sleep

After a short night, fasting often feels harsher: more cravings, lower tolerance for cold, and less patience.

What “Normal Cold” Feels Like Vs. A Red Flag

A mild chill that improves with layers, warm drinks, or light movement is usually not a crisis. Red flags are the cold feeling plus symptoms that point to low blood sugar or illness.

Signs That Fit A Typical Fast Adjustment

• Cool hands and feet, with steady thinking and stable mood
• A chill that fades after a warm shower, a walk, or adding a layer
• Feeling colder in the evening than midday

Signs That Suggest Low Blood Sugar Or Another Issue

Low blood sugar can bring sweating, shaking, fast heartbeat, hunger, and dizziness. The CDC lists common hypoglycemia symptoms and response steps. Low blood sugar (hypoglycemia) is a solid symptom list, especially for people with diabetes or those using glucose-lowering meds.

• Shaking, sweating, or clammy skin
• Lightheadedness, blurry vision, or confusion
• Weakness that hits fast, not gradually
• Fainting, new chest pain, or severe shortness of breath (seek urgent care)

How To Stay Warm While Fasting Without Breaking It

Your aim is to reduce heat loss, keep fluids and salt steady, and avoid pushing into a deeper deficit than you planned.

Warm The Core First

Start with socks and a warm layer around the torso. If your core is warm, hands and feet often catch up. A beanie or scarf can also help.

Use Warm, Calorie-Free Drinks

Hot water, plain tea, and black coffee can help you feel warmer. If coffee makes you jittery, switch to decaf tea or warm water.

Move For Five To Ten Minutes

Short movement bumps heat production. Think brisk walking, a few bodyweight squats, or light cycling. Keep it easy so you don’t crash later.

Time Your Meals To Reduce Night Chills

If you do time-restricted eating, many people feel warmer when they finish their last meal earlier in the evening. A steady dinner can reduce late chills and help sleep.

Table: Common Causes Of Feeling Cold While Fasting And What To Try

Likely Cause	What It Feels Like	What To Try
Less meal-related heat	Chilly in a room that used to feel fine	Warm drinks, extra layer, warm shower
Lower skin blood flow	Cold hands/feet, core feels okay	Socks, gloves, keep torso warm first
Low fluid	Cold plus low energy or headache	Water, warm tea, steady sipping
Low sodium	Lightheaded, weak, cold	Salt with care, ease up on sweat sessions
Big calorie gap	Cold all day, sluggish	Shorten the fast, eat enough on feeding days
Too much caffeine	Jitters, sweat, then cold	Lower dose, switch to tea, drink water
Poor sleep	Cold and cranky, cravings spike	Sleep more, run an easier fast next day
Low blood sugar risk	Shaky, sweaty, dizzy, confused	Check glucose if relevant, break the fast

Who Should Avoid Fasting Or Get Medical Oversight

Some groups have a higher risk of harm from fasting, mainly due to low blood sugar, dehydration, or medication effects. People with diabetes who use insulin or certain pills can face hypoglycemia during fasting windows. The NIDDK summarizes risks and counseling points for intermittent fasting in type 2 diabetes. Intermittent Fasting And Type 2 Diabetes covers those considerations.

If you’re pregnant, breastfeeding, underweight, have a history of eating disorders, or you take meds that affect blood sugar, blood pressure, or fluid balance, fasting may not be a good fit without clinician input.

Cold All The Time During Fasts: When To Check For Other Causes

If you feel cold on non-fasting days too, fasting may be revealing a separate issue. One common cause is an underactive thyroid, which can show up as cold intolerance and fatigue. Harvard Health notes missed meals and hypothyroidism among common reasons people feel cold. Why do I feel so cold all the time? explains typical causes and what clinicians often test.

Other causes include anemia, low calorie intake over weeks, and low protein intake. You don’t need to guess the cause. You can track the pattern: only fast days, or all days?

How To Break A Fast If You’re Cold And Not Feeling Right

If you feel shaky, sweaty, dizzy, or confused, treat it as a “break the fast” moment. Eat and drink, then reassess. If you have diabetes, follow your care plan and check glucose when you can.

Start Small And Gentle

• Water first, then a small meal
• Protein plus carbs tends to settle symptoms faster than fat alone
• Salted broth or a salty meal can help if you’ve been peeing a lot

Table: A Practical Cold-While-Fasting Checklist

Check	What To Look For	Adjustment
Clothing	Cold feet, bare ankles, drafty desk spot	Warm socks, base layer, keep torso warm
Fluids	Dry mouth, headache, darker urine	Warm tea, steady water through the day
Sodium	Lightheaded on standing, low energy	Add salt with care, ease up on long fasts
Caffeine	Jitters, sweaty palms, crash later	Lower dose, switch to decaf, drink water
Workout load	Cold after training, heavy fatigue	Train lighter while fasting, lift on fed days
Meal timing	Night chills or poor sleep	Shift dinner earlier, eat enough at dinner
Feeding-day nutrition	Low protein, low carbs, low micronutrients	Build meals around protein, fiber, and a carb source
Cold outside fasting	Cold even on fed days	Get labs and a clinical check

Pick A Fasting Schedule You Can Stick With

If fasting keeps making you cold, you don’t have to force longer windows. Many people do better with a gentler schedule, like 12–14 hours overnight, or fasting only on rest days. You can also keep the same window and raise calories on feeding days so the weekly deficit is not so harsh.

Test one change at a time: sleep, caffeine, sodium, workout load, or meal timing. If the cold feeling stays no matter what, switch plans or get checked for thyroid or anemia.