Why You’re Cold When Fasting: Tips From A Doctor

In recent years, fasting has seen a resurgence in popularity, being hailed for its potential health benefits, such as weight loss, improved brain function, and even increased longevity.

As a physician, I frequently encounter questions and concerns about the physiological effects of fasting. One issue that often surfaces is why do some people feel cold while fasting?

While this doesn’t happen to everyone, I indeed went through it at first, and still do if I neglect the tips we’ll discuss today. That’s what most of my client report as well.

The Importance Of Addressing This Issue

The reason I wanted to address this symptom today is that although common, can cause discomfort and concern among those who experience it.

Feeling chilly may seem like a minor nuisance compared to the touted benefits of fasting, but understanding its causes can shed light on the complex metabolic processes happening in our bodies during a fast.

Furthermore, it can help fasting individuals make more informed choices and manage this side effect more effectively.

Because in the end, who wouldn’t rather get rid of the cons and keep the pros of a diet? 😉

The Role of Blood Sugar Levels

Our bodies rely heavily on glucose as a source of energy. We obtain glucose from the food we eat, and it is transported via the bloodstream to the various cells throughout our bodies.

The level of glucose in our blood, or our blood sugar level, is, therefore, a critical component of our body’s energy management system.

When we eat, our bodies break down the carbohydrates in food into glucose, causing a rise in blood sugar levels. This glucose provides the energy that powers our cells and fuels our metabolism, contributing to heat production and maintaining body temperature.

However, during fasting, as the food intake stops, blood sugar levels gradually decline. As these levels drop, so too does the availability of glucose for energy production, leading to reduced heat production. Consequently, this drop in blood sugar may further contribute to those feelings of coldness experienced during fasting.

Understanding Fasting and The Body’s Energy Use

Our bodies are beautifully designed machines, powered by a complex system of energy utilization that ensures we can perform necessary daily functions. At the heart of this system is our metabolism, the process by which our bodies convert the food we eat into energy. Even when at rest, our bodies need energy for basic functions such as breathing, circulating blood, and cell repair.

Most of the energy we use is released as heat, a process known as thermogenesis. This heat helps maintain our body’s core temperature, keeping us comfortably warm. But what happens when we fast, and the supply of readily available energy from food is restricted?

During fasting, your calorie intake is significantly reduced or entirely eliminated for specific periods. Since calories from food are essentially units of energy, reduced caloric intake means there is less energy available for conversion into heat.

The immediate result is that we might find ourselves feeling a bit colder than usual. This is just the tip of the metabolic iceberg, though, as fasting triggers a host of other physiological changes in an effort to maintain balance and conserve energy.

The Impact of Fasting on Metabolism

In response to fasting, our bodies activate various adaptive mechanisms to ensure survival during periods of scarce food availability. One such adaptive strategy is slowing down the metabolic rate – the rate at which our bodies burn calories to produce energy.

Under normal circumstances, a faster metabolism equates to more heat generation, keeping us warm. However, during fasting, to conserve energy resources, our bodies intelligently ‘turn down the thermostat’, if you will. This slowed metabolic rate reduces the overall heat produced, which can lead to you feeling colder than usual.

The metabolic slowdown is a natural and expected response to fasting, a demonstration of the body’s remarkable ability to adapt to different circumstances. Nevertheless, this does not make the resulting cold any less uncomfortable for those experiencing it.

The slowdown of metabolism is just one piece of the puzzle. Let’s now turn our attention to another crucial piece: thyroid hormones.

Thyroid Hormones and Fasting

Thyroid hormones play a pivotal role in our bodies, controlling everything from our heart rate to our mood, and crucially, our metabolic rate. Produced by the thyroid gland, these hormones – primarily thyroxine (T4) and triiodothyronine (T3) – are instrumental in regulating our body’s energy use and heat production.

Under normal feeding conditions, these hormones keep our metabolic processes running smoothly, ensuring a consistent body temperature. However, during periods of fasting, the production of these hormones can decrease as part of the body’s adaptive response.

This decline in thyroid hormone levels during fasting can further contribute to the reduction in metabolic rate, enhancing the energy conservation strategy of our bodies. The result can be lower heat production, which, for you, may look like reaching for an extra layer of clothing.

Listening to Your Body During Fasting:

During my years of medical practice, I’ve observed that our bodies are incredibly adept at communicating with us, offering a wealth of information about our health and wellbeing. I’ve had patients come into my office with a variety of experiences related to fasting, and one common theme is the importance of tuning into these bodily signals and interpreting them accurately.

Let me share a few examples.

I had a patient who adopted a 20:4 intermittent fasting schedule right off the bat. She noted that she frequently felt cold during her fasting periods. This sensation, while not debilitating, was a persistent issue. It wasn’t until we discussed starting off slow and easing into a 16:8 pattern instead, that she started feeling better.

Another patient took on a more rigorous 5:2 fasting regimen. He reported not just feeling cold, but also experiencing bouts of dizziness and fatigue. These symptoms prompted us to reassess his fasting strategy, which eventually led to a modified, less stringent plan more suitable for his body’s needs.

Feeling cold during fasting, while common and usually harmless, could signify that your body is adjusting to the changes in your eating schedule.

However, if this sensation is paired with other symptoms like fatigue, excessive hunger, or dizziness, it might indicate that your body is under a certain level of stress. It’s crucial to pay attention to these signs and to respond appropriately.

Fasting is not a one-size-fits-all journey, and it should never compromise your overall comfort and well-being. That’s why I always remind my patients that the goal of fasting is to promote health, not to endure unnecessary discomfort.

If the cold sensation becomes too uncomfortable or is accompanied by other concerning symptoms, it may be time to re-evaluate your fasting schedule or seek professional advice.

Actionable Tips for Managing the Cold While Fasting:

Drawing on my experiences with patients and insights from various fasting strategies, here are some tips for dealing with the sensation of cold during fasting that you’ve been experiencing (and hating) for the last few days.

1. Combine Both Keto and Intermittent Fasting:

Adopting a keto diet in conjunction with intermittent fasting can accelerate your body’s adaptation process. Clients often find this combination particularly beneficial as it facilitates their body’s transition from relying on glucose to using ketones for energy.

We often conclude that navigating the dance of hormones, including growth hormone (GH) and insulin, becomes more manageable with this dual approach.

2. Increase Your Healthy Fat Intake:

When I first started doing both diets, I struggled with hunger since I had a smaller window to eat (thanks to I.F.) and fewer options of food to choose from (thanks to Keto).

By increasing my intake of healthy fats, I was able to supply my body with an alternative energy source, making the transition easier and satisfying my hunger.

3. Try Bulletproof Coffee:

A great aid in increasing healthy fat intake is Bulletproof Coffee. Not only does it help satiate your hunger, but it can also be enjoyed within your fasting window, helping you stick to your regimen.

I mean, this coffee is beyond me. I’m afraid that once you try it, you’ll never want to look back and prepare it yourself. This is how obsessed I know you’ll be with it. Have a look at it on Amazon.

However, as you’ll discover when you advance through the diet, while this beverage is extremely helpful in the early and late stages of the diet, this calorie-rich beverage may not be as beneficial during the weight loss phase.

4. Drink A Little More Water Than Your Body Asks For

On the topic of beverages, another critical factor is hydration. Your body might be secreting more water during this phase, and maintaining optimal hydration can help alleviate some of the common symptoms associated with transitioning into a state of ketosis, also known as the ‘keto flu’.

5. Aim At Getting At Least 7 Hours of Sleep:

Adequate sleep is vital during this transitional phase. Patient after patient has reported that ensuring they get at least 7 hours of sleep a night makes a significant difference in their energy levels and overall well-being during fasting and keto.

6- Replenish Essential Electrolytes

A critical aspect of maintaining well-being during fasting is managing your electrolytes. I’ve had many patients who found that increasing their intake of potassium-rich foods, like leafy greens and avocados, along with adequately salting their food, greatly aided their transition into fasting and keto.

Magnesium, available in foods like avocados, dark chocolate, salmon, almonds, and spinach, is another critical nutrient during this time. If you struggle to meet your electrolyte needs through whole foods, there are quality supplements available that can help.

7. Make Sure To Exercise (Do It Smartly Though):

Moderate exercise can be highly beneficial during fasting and the transition to ketosis. However, as I often find when returning to Intermittent Fasting, intense workouts can be counterproductive during the initial phase.

Light to moderate exercise sends a signal to your body that it is OK and prevents it from shifting into an energy conservation mode.

Nabeel Kallas

I'm a medical doctor with a lot of passion for Keto & Intermittent Fasting. They have completely changed my life and I am beyond honored to help you experience that same change. I'm ready when you are. Read more here.

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