Does ketosis make you cold? Unpacking the science behind the 'keto chills'

October 5, 2025 •

4 min read

Many people report experiencing flu-like symptoms, known as the 'keto flu,' when transitioning to a ketogenic diet. Among these effects, the sensation of being unusually cold is a common side effect, raising the question: does ketosis make you cold?. The answer is yes, for many, but this effect is typically temporary and a sign that your body is undergoing a significant metabolic shift.

Quick Summary

The feeling of coldness during the initial phase of ketosis is a temporary side effect of metabolic adaptation, as the body shifts from glucose to fat for fuel. Electrolyte imbalances, decreased metabolic rate, and altered thyroid hormone conversion contribute to this sensation, which typically resolves as the body becomes 'fat-adapted.'

Key Points

Metabolic Adjustment: Feeling cold is a common side effect during the initial adaptation to ketosis as the body switches from glucose to fat for energy.
Electrolyte Loss: The diuretic effect of ketosis can deplete essential electrolytes, impacting circulation and contributing to cold hands and feet.
Reduced T3 Hormone: The temporary decrease in the active thyroid hormone (T3) during carbohydrate restriction can lead to a lower basal metabolic rate and body temperature.
Fat Adaptation: As your body becomes more efficient at burning fat for fuel, typically after a few weeks, the cold sensation often subsides.
Manageable Symptoms: Proper hydration, electrolyte replenishment, and adequate fat intake are key strategies for mitigating 'keto chills'.
Keto Flu Symptom: The feeling of coldness is one component of the broader 'keto flu' syndrome experienced by many when first starting a ketogenic diet.

Understanding the Metabolic Shift in Ketosis

Ketosis is a metabolic state where your body shifts its primary fuel source from carbohydrates (glucose) to fat, producing molecules called ketones for energy. This process is a significant change for your body and can trigger a range of temporary side effects, often referred to as the 'keto flu'. The feeling of coldness, sometimes described as 'keto chills,' is one of the more noticeable symptoms during this transition.

The Impact on Your Body's Thermogenesis

During the first few days of a very low-carb, high-fat diet, your body is still figuring out how to efficiently use fat for fuel. Your cells are not yet fully optimized to burn ketones, which can lead to a temporary dip in overall energy production. This initial inefficiency can cause a transient reduction in your basal metabolic rate (BMR), the number of calories your body burns at rest. Since BMR is directly linked to body temperature, a lower metabolic rate can result in you feeling colder.

The Role of Electrolyte Balance and Hydration

One of the most significant changes that occur when starting a ketogenic diet is a rapid reduction in water retention. When you cut carbs, your body burns through its glycogen stores. Glycogen is stored with water, so as your glycogen levels deplete, your body flushes out this excess water through more frequent urination. This process can lead to the depletion of essential electrolytes, such as sodium, potassium, and magnesium. Electrolytes are crucial for many bodily functions, including nerve signaling and fluid balance, and their depletion can affect circulation and leave you feeling chilly, especially in your hands and feet.

The Thyroid Connection

Some research suggests that very low-carbohydrate diets can impact thyroid function, although the effect is often adaptive and not necessarily pathological. A sharp reduction in carbohydrates can lead to a temporary decrease in the active thyroid hormone, triiodothyronine (T3). This hormone is a key regulator of metabolism and body temperature, so a temporary drop could contribute to the cold sensation. However, studies show that thyroid-stimulating hormone (TSH) often remains stable, indicating that the body is adapting rather than developing hypothyroidism. For individuals with pre-existing thyroid conditions, such as Hashimoto's thyroiditis, the effects may be more pronounced, and medical consultation is essential.

Managing the 'Keto Chills': Practical Steps

Here are several strategies to help you manage and mitigate the cold sensation during the initial stages of ketosis:

Replenish electrolytes: Combat dehydration and mineral loss by supplementing with electrolytes or consuming mineral-rich foods. Bone broth, avocados, leafy greens, and nuts are excellent sources of sodium, potassium, and magnesium.
Stay hydrated: Drink plenty of water throughout the day. This is vital to replace lost fluids and can help maintain better circulation.
Consume adequate fat: Ensure you are eating enough calories and healthy fats. Insufficient calorie intake can further suppress your metabolism. Healthy fats from sources like coconut oil, avocado oil, and nuts are important for maintaining energy levels.
Engage in light exercise: Gentle activities like walking or yoga can help stimulate circulation and generate some body heat. Avoid strenuous exercise during the adaptation phase, as it can be too taxing.
Enjoy warm beverages: Sipping hot herbal tea or bulletproof coffee can help warm you from the inside out. Be mindful of caffeine intake, especially if you experience sleep issues.
Dress in layers: Wearing warmer clothing and dressing in layers can provide easy relief by helping your body conserve heat.

Comparing the Keto Transition vs. Fat-Adapted State


Feature	Initial Keto Adaptation	Fat-Adapted State
Primary Fuel Source	Transitioning from glucose to ketones.	Efficiently utilizing fat and ketones for fuel.
Energy Production	Inefficient, leading to fatigue and reduced metabolic rate.	Efficient and stable, providing sustained energy levels.
Body Temperature	Often feels colder due to temporary metabolic slowdown.	Body temperature typically normalizes or can even increase due to efficient fat burning (thermogenesis).
Electrolyte Balance	Prone to deficiencies due to increased water excretion.	More stable with consistent electrolyte intake.
Keto Flu Symptoms	Common to experience headaches, fatigue, and chills.	Symptoms largely disappear as the body adapts.
Thyroid Hormones	Active T3 may temporarily decrease.	T3 levels tend to stabilize or stay adaptively lower, not pathologically.

Conclusion

Feeling cold is a common and often temporary symptom of transitioning into ketosis, not a permanent or inherently harmful side effect. It is primarily driven by your body's metabolic adjustment, which includes a temporary reduction in metabolic rate and fluid loss that affects electrolyte balance. Addressing these underlying factors by prioritizing hydration, consuming sufficient healthy fats, and replenishing electrolytes can significantly alleviate the sensation of coldness. As your body becomes fully fat-adapted, this symptom typically subsides, and many individuals report increased overall energy and improved temperature regulation. If the cold sensation is severe, persistent, or accompanied by other concerning symptoms, it is always recommended to consult a healthcare professional to ensure no underlying issues exist.

For more detailed information on the metabolic effects of ketogenic diets, you can review the extensive research available at the National Institutes of Health.

Frequently Asked Questions

During the initial phase, your body reduces energy production while it adapts from using glucose to burning fat for fuel, which can temporarily lower your metabolic rate and cause you to feel colder.

Yes, for some people, feeling cold can be a sign that their body is entering ketosis and shifting its primary energy source. It's often part of the temporary 'keto flu' experience.

The sensation is typically temporary, lasting a few days to a few weeks, as your body adapts and becomes more efficient at using fat for energy.

Yes. When transitioning to ketosis, the body flushes out a lot of water, which can lead to a loss of key electrolytes like sodium, potassium, and magnesium. This can affect circulation and contribute to feeling cold.

Some studies show that very low-carb diets can temporarily reduce the level of active thyroid hormone (T3), which can affect body temperature. However, TSH levels typically remain stable, indicating an adaptive rather than pathological response.

You can help regulate your body temperature by staying well-hydrated, replenishing electrolytes, consuming enough healthy fats, and incorporating light exercise as you adapt.

It's a common and usually normal adaptation phase. However, if the cold sensation is extreme, persistent, or accompanied by other severe symptoms, it is recommended to consult a healthcare provider.

Yes, as your body becomes more efficient at using fat and ketones for fuel, energy production becomes more stable. Many individuals find that their body temperature normalizes or even increases after becoming fully fat-adapted.