Athletes who swim long distances in open water often lubricate their bodies with (animal) fat as insulation. In order to protect their body against the low temperature of the water while swimming. But their own body fat also helps them to stay warm. Scientific research has also shown that swimmers with a higher body mass index (BMI) appear to have a lower risk of hypothermia.
Patients treated with ‘therapeutic hypothermia’ after cardiac arrest to prevent brain damage and inflammation after cardiac arrest, also experience the same effect. Studies show that obese patients take longer to reach this state of hypothermia because their extra fat seems to isolate the body.
Yet there are circumstances in which overweight people feel colder than people of so-called average weight. This is caused by the brain combining the signals from the temperature of the body and the temperature on the surface of the skin. With this, the body determines when to constrict the blood vessels (to limit heat loss through the skin) and cause chills (to generate heat). Because the body of an obese retains their fat subcutaneous, the core will tend to stay warm while the skin cools down.
There are also other factors besides subcutaneous fat that help to determine the rate at which our body cools down. For example, smaller people, who have more skin surface compared to the total volume of their body, lose heat more quickly. This can also be a reason that women feel colder than men because they are smaller on average and average body size can play a role. In addition, a muscular physique can offer some protection against hypothermia because the muscle tissue partly generates heat.