Why Do You Feel Cold While Fasting?

author avatar Dr. Eric Berg 08/31/2023

If you are feeling cold while fasting it’s because your body undergoes many changes when you fast; your metabolism taps into fat stores, your blood flow redirects towards adipose tissue, and your digestive system idles, generating less heat.

All of these changes can make you feel cold as your body becomes fat-adapted. Discover more about these fascinating processes and what you can do if you feel cold while fasting.

Feeling cold while fasting


What is fasting?

Fasting is when you stop eating. The duration of a fast can vary depending on its purpose.

Intermittent fasting (IF) is an excellent way to lose weight and support a healthy body. This is a pattern of eating that alternates between periods of fasting and eating. 

Intermittent fasting can be as simple as skipping breakfast and having your first meal of the day at noon and your last meal at 6:00 pm—with no food or calorie-rich beverages outside of this window. This is known as an 18:6 fast. You get 18 hours of fasting with a 6-hour eating window.

Intermittent fasting is focused on when you eat rather than what you eat. 

Several studies show intermittent fasting helps you lose weight, including forty studies in a systematic review. The average weight loss over ten weeks was 7 to 11 pounds. 

Is it normal to feel cold while fasting?

If you feel chilly when fasting, you’re not alone. While some people experience cold hands and feet, others feel cold throughout their whole body.

Though it may be uncomfortable, it’s normal to feel chilly while fasting. This indicates that your body is diverting the energy meant for heat generation to fat burning.

During fasting, your blood sugars drop. This is the goal—you want to lower insulin and blood sugar levels to enter fat-burning mode. 

It’s important to ease into your fasting plan so your blood sugar doesn’t drop too quickly.

If you have low blood sugar from fasting, your body hasn’t fully adapted yet—and if you notice symptoms like sweating, dizziness, and shaking, you should end your fast.


Fat adaptation

Four reasons why you feel cold while fasting

What really happens when we fast? There are many reasons why you can feel chilly while fasting—we’ll cover the four most common reasons here.


1. Fat adaptation

When you start intermittent fasting, your liver converts your stored fat to energy since no energy is generated from food. The metabolic adjustment of your body to this process is called fat adaptation.

During the fat adaptation process, your body system uses the adipose tissue blood flow (energy meant to keep your body warm) for the conversion of white fat (fat around your hips, belly, and vital organs) to energy. Thus, your body temperature drops, and you feel chilly.

It can take up to 4 to 12 weeks to become fully fat-adapted. Some factors that influence the duration may include age, menopause, history of carb consumption, and slow metabolic rate.


2. Lack of heat from digestion

The chemical responses in your digestive system during digestion cause your body temperature to increase. This is why you may start sweating after eating a large meal.

It takes 6 to 8 hours for your digestive system to process nutrients—and chances are, you will eat another meal before the last one is fully digested. This makes digestion a nearly continuous process.

But you don’t have to digest food when you fast, so your body cools down. This is less noticeable when you’ve become fully fat-adapted. 


3. Redirected blood flow

Blood flows toward brown adipose tissue when you fast. This unique form of fat breaks down glucose and stored fat to regulate your body temperature.

Brown fat also helps transport energy from fat stores to your muscles as a substitute for the energy you normally get from food.

While a primary function of brown fat is to produce heat, you can temporarily feel cold as the blood flow that normally keeps your hands and feet warm is redirected to brown adipose tissue.

This effect isn’t lasting—you'll warm back up as your body adapts to fat burning.

4. Nutrient deficiencies

Vitamins and minerals are essential for body heat regulation. Many nutrients are stockpiled in fat tissue—especially fat-soluble vitamins. 

As you burn body fat on keto and intermittent fasting, you also lose many of these stored nutrients. This can significantly increase your nutrient requirements until you become fully fat adapted.

You can also lose a significant amount of water weight within the first week or two of intermittent fasting, which will flush out water-soluble nutrients. 

It’s crucial that you replenish your vitamins and minerals with nutrient-rich foods and a high-quality supplement while fasting.

You may feel extra chilly when deficient in vitamins and minerals that support thyroid function, like iodine, selenium, and zinc.


Other causes of feeling cold:

  • Iron deficiency (or low-iron anemia) can cause low blood circulation and coldness.

  • Low vitamin B1 can cause Raynaud's syndrome. This condition restricts blood flow to your fingers and toes, making them feel cold and turn blue until you warm up.

  • Chromium deficiency can contribute to insulin resistance. This important mineral makes insulin receptors more sensitive. If you have insulin resistance, low chromium may extend the time it takes to become fat adapted.

  • A deficiency in B vitamins may cause you to feel cold. B vitamins are essential for cellular energy production.

Intermittent fasting


Should you stop fasting if you feel cold?

Feeling cold when fasting is a temporary response to fat adaptation. Stopping keto and intermittent fasting when you feel cold could extend the adaptation stage and slow your results.

You can use the tips later in this article to help warm yourself up until your body temperature normalizes on its own.


If you still feel cold beyond the fat-adaptation stage, consult your doctor to find out what else could be going on.

How long does it take to adapt to a keto diet?

Keto adaptation typically takes 2 to 3 weeks, but it can take up to 6 weeks to become fully adapted if you have severe insulin resistance.

Your body needs this time to adjust to using ketones instead of glucose. Meanwhile, be sure to stay consistent and committed to achieving your health and weight loss goals.

Keep an eye out for these signs that you’re fully keto-adapted:

  • You no longer experience keto flu

  • You have more mental clarity

  • You’re sleeping better

  • You have zero cravings for carbs

  • You no longer feel hungry between meals

  • You don't have a headache or symptoms of low blood sugar

  • You no longer have low energy from extended fasts


Warm and cozy home

How to warm up while fasting

If you need to warm up while fasting, use the tips below.

Combine keto and intermittent fasting

Combining keto and intermittent fasting is the best way to speed up adaptation. Keto foods are packed with fat and nutrients to help you fast for longer in a healthy way. 

Just keep in mind that consistency is key. Once you’ve become fully fat-adapted, your body will no longer feel cold from fasting.

Increase your fat intake

You need enough calorie intake to generate body heat. So during your healthy eating window, you can increase your calorie intake to keep your body warm ahead of the fasting phase. 

Make sure to include plenty of healthy fats in your meal. Avocados, cheese, whole eggs, and fatty fish are excellent sources of fat.

Replenish nutrients

Incorporate nutrient-dense foods and electrolytes into your keto plan.

Nutritional yeast is a great source of essential B vitamins needed to transition from burning glucose to fat. Dark leafy greens are also a great source of essential minerals and vitamins.

Get your body moving

Low-intensity exercise can help combat feeling cold while fasting. You don't have to run or lift weights—walking or mild yoga should be enough to warm you up. 

If you sit for most of the day at work or home, try getting up every hour to move around and stretch your legs.


Enjoy a hot beverage

A hot beverage can warm up your body temperature and make you feel cozy. If you struggle with cold fingers, try holding a warm mug to heat up your hands.

Green tea and coffee without sugar are great keto-friendly options—and they have many health benefits.


Wear warm clothing

Warm clothing will help retain your body heat. You may even feel comfortable in long-sleeve shirts and pants in the middle of summer during the keto adaptation phase.

Clothing made of materials like wool, silk, or polypropylene will have a better effect than clothes made of cotton.

Take a hot shower

A warm bath or hot shower will quickly raise your body temperature and help you fight against the cold. To get the most out of your warm bath, keep the door closed and let the steam build up.

Taking a hot shower has many other benefits besides keeping your body warm. It kills bacteria, aids relaxation, and can elevate your mood.

Add some spice

Spicy foods and beverages stimulate blood circulation and help raise your body temperature. 

Try integrating spicy foods into your ketogenic diet to generate more body heat just before your fast. If you’re in the middle of your fasting window, you can try adding some spice to a chai or ginger tea. 


Adjust the AC

If all else fails, you may just have to warm up the temperature in your home or office until your body becomes keto-adapted.

And if you still feel chilly after turning off the AC, try using a space heater.


Keto fat burning


Key takeaways

It’s normal to feel chilly during the early stage of keto and intermittent fasting. When prolonged fasting, your body is adjusting to your new plan and it can take up to six weeks for your body to become fully fat adapted.

Nutritional deficiencies, blood redirection, a lack of heat from digestion, and low blood glucose and insulin can all affect your temperature when you start fasting.

There are many ways to avoid feeling cold while fasting. You can try moving your body, drinking hot tea or coffee, eating healthy during the eating window, or wearing warm clothes. 

Give these tips a try and remember that feeling chilly is only a temporary effect of keto and fasting—so don’t give up! You’re on your way to a healthier and thinner you.


1. Is it normal to feel cold while doing intermittent fasting?

Yes, it’s normal to feel chilly at the early stage of intermittent fasting—it’s a sign you’re losing fat. If you’re fully fat-adapted, talk with your doctor if you still feel cold.


2. Why do I feel cold while doing intermittent fasting?

You often feel cold while fasting because your body isn’t fully fat-adapted. It can take up to six weeks to adapt to ketosis.


3. How can I avoid feeling cold while fasting?

You can warm up your body while fasting by wearing warm clothes, taking a bath, drinking hot tea, exercising, and replenishing vitamins and minerals.


4. Can nutrient deficiencies make you feel cold?

Yes, a lack of essential nutrients can lower body temperature. Iron, B vitamins, and chromium are important for body temperature regulation. 


5. Why does fat adaptation make you cold?

Many factors affect your temperature while becoming fat-adapted, including lower insulin and blood glucose levels, a lack of heat from digestion, nutrient deficiencies, and redirections of blood flow.


6. Is being cold a sign of ketosis?

Yes, being chilly could be an early sign of ketosis. At this stage, your body switches from using glucose to burning body fat.


7. Should I stop fasting if I feel cold?

No, you don't have to stop a fast when you feel chilly—it could just be a sign that you’re losing fat. 


8. Does ketosis affect your body temperature?

Yes, you tend to feel chilly while in ketosis—especially during the early stages. This can be because of blood sugar decreases, a lack of digestion, or a redirection of blood flow. 


9. Can a low-carb or keto diet make you feel cold?

Yes, a low-carb or ketogenic diet can temporarily cause a lower body temperature as you adapt to ketosis.

10. How long does it take to adapt to ketosis?

It typically takes two to three weeks to become keto-adapted—but in some cases, it can take up to six weeks.

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