Cold When Fasting – Intermittent Fasting Side Effects 2023

Ellie Busby

Updated on - Written by
Medically reviewed by Kathy Shattler, MS, RDN

cold when fasting

Intermittent fasting has a range of verified health benefits, from losing weight to boosting the immune system to living longer. But intermittent fasting isn’t without its side effects

One of the main symptoms people face is feeling freezing cold when fasting — even with the heating turned up. Because of this side effect, some people even give up intermittent fasting, usually before the benefits of fasting start to show

But we don’t want you to miss out on all the health benefits of fasting because of cold toes. In this article, we explain why you feel cold while fasting, how long this side effect lasts, and how to start feeling warm again.

Does Fasting Make You Feel Cold?

Yes, fasting can make you feel chilly — especially when you first start intermittent fasting. This is because your body is adapting to a new eating habit.

There are different types of intermittent fasting methods, including

  • Alternate-day fasting, where you restrict your calories to 20-25% every other day.
  • Time-restricted feeding, where you fast for a set number of hours every day, such as the 16/8 method.
  • The 24-hour protocol, where you fast for 24 hours every week or month.
  • The 5:2 diet, where you restrict your calories to 20-25% of normal for two non-consecutive days per week. 

However, no matter which fasting method you go for, you’ll likely feel chilly during the fasting period in the first days or weeks. Here’s why.

Fasting Restricts Calories

During fasting, you’ll severely restrict your calories at certain times. Studies suggest that calorie restriction decreases core body temperature[1] and skin temperature.[2] You’ll feel it most in your extremities — fingers, toes, maybe your entire feet and hands. 

Fasting Slows Your Metabolism

Intermittent fasting reduces metabolic rate,[3] hence reducing energy expenditure[4] and conserving calories. 

It’s because your body isn’t used to being without calories for so many hours. Studies in animals show that even short periods of reduced food availability trigger a state of torpor[5] — the reduced metabolic rate and body temperature associated with hibernation. Similarly, your body, thinking it’s in a famine, triggers a state of torpor to reduce energy usage and improve your chances of survival. This is called adaptive thermogenesis.[6] 

You might be worried that a slower metabolic rate increases your risk of weight gain. However, your metabolism should only be slower when you start fasting and should start changing after a few days when your body adapts to fat burning. Overall, fasting is associated with increased fat loss and better body composition than a normal calorie-restricted diet.

Fasting Lowers Blood Pressure

Fasting is associated with reduced blood pressure,[7] making you feel colder. A common symptom of low blood pressure is feeling chilly — especially having cold hands and feet. The reason? Reducing blood flow to your extremities will conserve calories to keep your vital organs going. 

Fasting Lowers Blood Sugar

Another reason for being cold during fasting periods is low blood sugar.[8] If your body isn’t used to fasting, it hasn’t yet adapted to fat-burning to produce energy.[9] It’s still in carbohydrate-burning mode. 

But fasting increases glucose uptake[10] and uses up your carbohydrate stores, leaving your body with nothing to keep your blood sugar levels balanced. Hence, your blood sugar decreases, and your metabolic rate slows down, making you feel cold. That’s until you become fat-adapted.

Fasting Increases Fat Loss

Actually, feeling a bit chilly might not be a bad thing. In fact, it can be a sign that your body is starting to adapt to fasting.[11] Being cold[12] speeds up changes in fat tissues, which benefits your metabolism. 

As your body gets used to fasting and starts burning fat for energy, your blood flow changes. Instead of going to your fingers or toes, it flows to your fat stores. This is known as adipose tissue blood flow, and it’s important to ensure your muscles receive energy as fat from your fat stores. 

This adaptation to burning fat via increased adipose tissue blood flow might be why intermittent fasting increases body fat loss[13] over standard calorie restriction. 

But, of course, as you lose body fat, you’ll also lose your natural insulation and feel colder. Time to layer up!

How Long Will The Chill Last?

You’ll be glad to hear that chills while fasting do not last long. Once your body gets used to living without constant food by burning fat instead of carbohydrates, your metabolic rate should normalize. 

Studies suggest that most of the adverse effects of intermittent fasting improved[14] after one month. And your body temperature might improve even faster.

One study in obese women found that, compared to those who simply restricted daily calorie intake, those who fasted for 12 hours per day had a significantly higher skin temperature[15] after just three weeks.

How To Stop Feeling Cold When Fasting

There are several steps you can take to reduce the side effects[16] of intermittent fasting, such as feeling cold, so you can enjoy the health benefits.

“I’m Freezing Cold When I Fast — What Should I Do?”

  • If doing time-restricted feeding, start your eating window earlier in the day. Late-night food consumption has been shown to increase body temperature at night and reduce sleep quality.[17] Hence, while intermittent fasting, it makes more sense to start eating food earlier in the morning and finish in the afternoon, leaving the drop in body temperature for night-time when you’re sleeping anyway.
  • Go to bed early to take advantage of your lower body temperature to help you sleep.[18] Your core body temperature has a daily cycle, which helps control your circadian rhythm. Namely, your temperature decreases when you sleep, and a rise in temperature helps wake you up in the morning. 
  • Eat frequently during feed periods.
  • Avoid long periods of sitting or inactivity. For every minute spent doing warm-up exercises, body temperature increases[19] by 0.1 degrees Celsius. In fact, one fasting study that included daily moderate physical activity found that less than three percent of participants reported feeling cold.[20]
  • Rather than a high-glycemic meal, break your fast with a high-protein meal[21] to optimize blood sugar balance.
  • Turn up the heating or use a hot water bottle.
  • Drink hot beverages such as tea or coffee.
  • Wear more layers.

Is It Normal To Be Cold During A Fast?

Yes, having chills while fasting is normal. Fasting can make you feel chilly because your body’s metabolism is changing. While that happens, your blood flow is being redirected from your extremities, your blood sugar might be low, and your digestion stops.

However, if you follow a safe intermittent fasting protocol that doesn’t restrict calories too much and includes regular physical activity, you should feel warmer.

Also, the side effects of intermittent fasting tend to subside within one month, so even if you feel cold now, your body should adapt. In fact, studies show that long-term intermittent fasters have a higher body temperature than those on a calorie-restricted normal diet.

If you still feel cold after one month of intermittent fasting, ensure you’re eating enough food and getting regular exercise. If intermittent fasting does not suit you, you could try other methods of losing weight, such as supplements to boost fat burning.

If you have other symptoms of very low blood sugar, such as feeling clammy, light-headed, or nauseous, make sure to eat something. Ongoing symptoms of very low blood sugar, especially if not relieved by food, should be discussed with your doctor.


+ 21 sources

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Ellie Busby

Written by:

Ellie Busby, MS, RDN

Medically reviewed by:

Kathy Shattler

Ellie Busby is a Registered Nutritionist (MSc, mBANT) and nutrition writer. She holds a bachelor's in Chemistry and a Masters in Nutrition. Ellie specializes in plant-based nutrition for health and fitness. She is also the Founder of Vojo Health, a personalized nutrition service based on genetic testing.

Medically reviewed by:

Kathy Shattler

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