The latest research is focusing on central heating as one of the causes of worldwide, and rising, obesity.
Because people spend time in heated cars and buildings, they use less energy in keeping warm than in the past. The energy expended as heat would have spent many calories of energy that are stored as fat instead.
The dangerous effects of cold were a threat to the survival of our primitive ancestors. The body evolved its own heat-generating system, a specialized fatty tissue known as brown adipose tissue or BAT. This maintains a constant internal temperature by generating heat.
Until recently it was believed that only new born babies had BAT, which was gradually lost so that adult humans had none.
But chance observations during routine scans of hospital patients showed this to be untrue – many adults have BAT.
BAT is a major contributor to metabolic rate, using an estimated 14 to 30 per cent of daily energy in various studies under different conditions. This means that from several hundred to over a thousand calories of energy could be expended daily by activating this tissue.
And research has so far shown that when BAT is increased it does not automatically lead to increased eating. The potential fat-burning effect is vast.
However, the highest concentrations have been found in lean people, while the obese can have very little or none. In one experiment, when obese subjects were exposed to cold, heat production from BAT was detected in only three out of 15 subjects.
Some scientists suggest that fatter people have less BAT due to the “thrifty gene” theory. This states that people become obese because they have a superbly adapted physiology evolved over millions of years to reduce the energy expended by the body.
If energy is more efficiently used, fewer calories of food are needed and famine can be endured and thus survival of the species is assured.
The obese therefore become so because their bodies have found other ways of regulating body temperature in cold climates and their BAT is genetically inactive. They burn less energy as heat and so have slower metabolisms.
Many critics find this theory unconvincing because lowering of the temperature reactivates BAT. It expands or contracts in all mammal species according to seasonal temperature variations.
Lean people have greater stores of it, possibly because they don’t have the insulation of fat to keep them warm. It would seem likely that people insulated with fat have less need for it and so it atrophies. Plus it has also been established that white adipose tissue or WAT, the ordinary fat that many of us are trying to get rid of, can be converted into BAT by the body.
Studies suggest that the likely scenario is that the body adapts to an artificially held constant ambient temperature and consequently BAT becomes less active.
Beyond its heat generating effect, BAT has been found to have other important functions relevant to fat loss. It regulates energy intake and burns fats and sugars at a vigorous rate and so could be very important in preventing diseases like metabolic syndrome and type-2 diabetes.
In situations where BAT has been removed, insulin resistance (the precursor of diabetes) and obesity develop, and if BAT is transplanted into an individual with insulin resistance and obesity, normal insulin balance is restored and fat loss occurs.
Is it possible to increase the activity of BAT in overweight subjects? While trials have yet to be published that definitely show that this is possible, it looks a promising area for investigation and personal experimentation. In addition, to experience a range of temperatures and to be physiologically adaptable to them is in greater accord with our evolutionary design.
Turning the central heating down a few degrees or going out for walks in cooler weather without overdressing could help to make the tissue more active. Cool or cold showers probably have an effect because research demonstrates that BAT becomes activated when just one arm is placed in very cold water. But ice cold water immersion can be dangerous because it creates dramatic spikes in blood pressure, so it’s wise to choose a safe water temperature.
What if we really can raise our metabolic rate and burn food energy more effectively and enhance our insulin sensitivity? That would prevent the development of diseases like type-2 diabetes, heart and circulatory disease, breast cancer and macular degeneration.
Enhancing the effectiveness of brown adipose tissue could be the key to fat loss and prevention of many common modern day diseases.