The ketogenic diet fundamentally alters the body’s primary energy source, shifting it to a state of nutritional ketosis. This diet involves consuming very high amounts of fat, moderate protein, and severely restricting carbohydrate intake. While many focus on the benefits of this metabolic shift, a common, temporary side effect is an increased sensitivity to cold, sometimes called “keto cold.” This phenomenon results from physiological and hormonal adjustments the body undergoes when it transitions from burning glucose to utilizing fat and ketones for fuel.
Metabolic Shift and Reduced Heat Generation
The primary reason for feeling colder on a ketogenic diet relates to a change in how the body generates heat from its fuel sources. When the body primarily runs on carbohydrates, metabolizing glucose is relatively inefficient, resulting in a higher amount of energy being released as heat (the thermic effect of food).
When carbohydrate intake is severely limited, the body switches to burning fat and producing ketones. This switch makes energy production more efficient, meaning less energy is wasted as heat during metabolism. The body’s Basal Metabolic Rate (BMR), the energy expended at rest, can also decrease as an adaptation to weight loss or perceived energy restriction.
This reduction in BMR is a survival mechanism, as the body attempts to conserve energy stores when fuel availability changes dramatically. Since less fuel is burned to maintain basic bodily functions, the overall production of internal body heat is lower. This metabolic slowdown translates directly into a noticeable feeling of coldness, particularly in the extremities like the hands and feet.
Hormonal and Electrolyte Impacts on Temperature Regulation
Beyond the efficiency of fuel burning, the shift to a ketogenic state impacts two other systems that govern internal temperature: hormones and electrolytes. The thyroid gland, which regulates metabolism and body temperature, is sensitive to carbohydrate restriction.
During the initial adaptation phase, many people experience a temporary reduction in the active thyroid hormone, triiodothyronine (T3). This decrease is likely an adaptive response, as T3 levels often correlate with glucose metabolism, and lower levels help conserve energy when carbohydrates are scarce. Because T3 regulates the body’s metabolic thermostat, its temporary suppression can contribute significantly to cold intolerance.
The rapid loss of water and minerals also plays a role in feeling cold. The ketogenic diet’s low carbohydrate intake causes a drop in insulin, which signals the kidneys to excrete more sodium and water. This diuretic effect can quickly lead to dehydration and a deficiency in key electrolytes like sodium and potassium. Electrolyte imbalances and dehydration impair blood volume and circulation, reducing the efficiency of heat distribution throughout the body and exacerbating feelings of being chilled.
Practical Adjustments for Managing Cold Sensitivity
To mitigate the feeling of coldness, dieters should ensure their overall caloric intake is adequate. Unintentional calorie deficits will signal the body to further slow its metabolism, worsening the cold sensation. Consuming enough calories, primarily from healthy fats and moderate protein, supports energy needs and prevents an extreme drop in BMR.
Addressing the fluid and mineral imbalance is important for temperature comfort. It is helpful to actively increase the intake of sodium, potassium, and magnesium, as the kidneys excrete these at a higher rate on a ketogenic diet. This can be achieved through adding salt to meals, drinking mineral-rich bone broth, and consuming keto-friendly foods high in these minerals.
Maintaining proper hydration by drinking sufficient water throughout the day is necessary to restore blood volume and improve circulation. The cold feeling is often most pronounced during the first few weeks, coinciding with the “keto flu,” but typically subsides once the body has fully adapted to using fat and ketones as its primary fuel source.
Identifying When Coldness Requires Medical Attention
While mild cold sensitivity is a common side effect of metabolic adaptation, persistent or severe coldness, especially with other symptoms, can signal a more serious issue. If the cold feeling is debilitating, or if it extends far beyond the initial adaptation phase (four to six weeks), a medical consultation is warranted.
Symptoms such as profound fatigue, hair loss, changes in skin texture, or persistent mental confusion alongside cold intolerance should be evaluated. These signs might suggest an underlying thyroid dysfunction or a hormonal imbalance that requires medical intervention. Consulting a healthcare provider can help rule out other conditions and ensure the diet is not negatively impacting overall health.