Feeling cold is one of the side effects of bariatric surgeries such as a gastric sleeve. The gastric sleeve surgery has become the most commonly performed weight loss surgery in the United States due to its relative safety, effectiveness in achieving significant weight loss and reversing comorbid conditions with the attendant reduction in the cost of healthcare and prolonging the life of obese individuals.
Weight loss surgeries including gastric sleeve can reduce weight by reducing the availability of calorie thus necessitating the mobilization of fat for energy production. This implies that as you lose weight, the quantity of fat in different parts of the body gradually reduces. Fat is known to serve as an insulator. The feeling of cold after gastric sleeve surgery is therefore not unconnected with the function of fat in the regulation of body temperature.
How is heat generated in the body?
Virtually all metabolic reactions in the body are energy dependent. The breakdown of food molecules result in energy production, but due to the inefficiency in harnessing this energy, a considerable amount is lost as (converted to) heat. This heat can either be conserved to maintain the body temperature or dissipated.
How is the body temperature regulated?
Animals maintain their body temperature by various means including hibernation during cold seasons. We can keep our core body temperature despite wide variations in our environmental temperature. The regulation of body temperature in humans is a function of a part of the brain known as the hypothalamus. This area of the brain functions as the thermostat receiving inputs about the body temperature of nerve cells that are identified as thermoreceptors. There are cold and heat receptors in the skin and other inner organs.
When the body temperature is getting low, the cold receptors are stimulated and in turn, send this information to the spinal cord for onward transmission to the hypothalamus. Likewise, elevation of the body temperature above the set point will stimulate the heat receptors, and the information will be transmitted to the hypothalamus. The information, therefore, determines the response of the hypothalamus it receives from the thermoreceptors.
How does the body respond to temperature changes?
The process of heat loss from the body can be by conduction, radiation or evaporation. When the body temperature rises beyond the set point, the hypothalamus sends impulses to the appropriate brain centers which in turn results in vasodilatation of the cutaneous arterioles (small arteries in the skin). This increases the blood flow with heat being transferred to the skin. The consequence is excessive sweating. Evaporation of the sweat from the skin surface results in cooling.
When the body temperature is lower than the setpoint, the response is vasoconstriction and reduction in blood flow to the skin to minimize heat loss. The body can also generate heat by muscle contraction (shivering).
Peculiarity of heat regulation in obese individuals
Obese people often generate a higher amount of heat energy than their healthy weight counterparts. The basal metabolic rate is higher in obese people thus resulting in more heat production. The excess fat in them is a poor conductor of heat and therefore serves as “insulator” preventing obese individuals from losing the excess heat to their environment by conduction. The increase in body mass in them is accompanied by a relatively lower increase in body surface area (because the height remains constant). This implies that obese individuals will lose less heat as heat loss is proportional to the surface area of the skin. In summary, excess fat keeps you warm.
What happens after gastric sleeve surgery?
You generate less energy
Losing weight only means that your body now requires less power to keep you in optimal condition. The basal metabolic rate and energy production reduces, leading to less heat production.
You lose fat
Weight loss occurs after gastric sleeve surgery due to the low-calorie intake. Your body, therefore, turns to the stored fat as a source of energy. The fat under your skin is the first to be used up. The insulation provided by these fat pads is lost leading to more significant heat loss from the body than before.
The cold receptors then pick this information whenever the body temperature is low and send it to the hypothalamus. The body tries to generate heat by muscle contraction leading to shivering, and blood flow to the skin is reduced by vasoconstriction. You may also develop goose pimples from contraction of the smooth muscles associated with hair follicles.
In summary, feeling cold after gastric sleeve surgery is due to low heat production and loss of insulation both as consequences of fat loss. You can keep yourself warm by putting on multiple layers of clothes. It is a transient feeling that you will overcome as your thermoregulation gets adapted to your new weight.