Losing fat by being cold?

When we are exposed to cold, a series of adaptations take place that could lead to the loss of fat tissue, but how relevant can this be? 

Cold exposure is a manipulation of thermoregulation in the extreme of lowering the temperature by changing the external temperature, Cold exposure attempts to achieve certain cellular effects that can be used to achieve one’s goals.

Thermoregulation 

Almost half of the caloric expenditure is used to keep our body at 37 degrees Celsius, especially the mid zone, interestingly obese people tend to have a lower mid zone temperature than non-obese people (1).

Unfortunately thermoregulation is different in modern life, we spend more time in temperate zones than being exposed to the cold. 

An adult person with a low fat percentage has about 130,000 kcal stored in the form of adipose tissue while an obese person has about 1,000,000 kcal stored.    

Not all fat cells are the same

There are different types of adipocytes that make fat tissues different, which affect the body in different ways. 

We have white fat, brown fat, then we have brite (Brown in White), IBAT, Recruitable BAT and Wbat.

Lately, metabolically active tissue (BAT and beige) is being explored as targets for increasing energy expenditure and fat loss. 

White adipose tissue or white fat

White adipose tissue is a powerful endocrine organ and is the most abundant in our bodies. When levels are too high or too low it can lead to inflammation, insulin resistance, poor blood sugar control and decreased sex hormones among other things. 

Brown or brown fatty tissue 

This tissue is rich in mitochondria and capillaries (much more than white fat), its main role is to produce heat.

Brown fat uses macronutrients to produce heat instead of ATP thanks to a protein called uncoupling protein 1 or UCP1. 

Adults have less brown adipose tissue than neonates, because an adult is less likely to die from hypothermia. 

Brown fat can be increased at temperatures from 15 degrees Celsius up to a maximum of 18 degrees Celsius where the greatest benefits have been seen, the difference is in the exposure time (lower at lower temperatures and higher at higher temperatures respectively).

Effects of cold exposure on brown fatty tissue

In one study, 10 days of exposure to 15.5 degrees increased brown fat volume by 37% (2), although this test did not show whether there was an increase in caloric expenditure. 

A shorter 3-day test at 16°C showed an increase in caloric expenditure of 140kcal/day (3).

There are tests that have shown a caloric expenditure of 400kcal with only 2 hours of exposure to 18.8 degrees Celsius, although the comparison was not of good quality since in this test the exposure to cold was alternated by putting the feet in ice compared to the same but without putting the feet in ice at 27 degrees Celsius (4).

While exposure to cold increases BAT activity, (especially thermogenesis not associated with shivering) there is no clinical evidence to support this as a method of fat loss (5,6). 

Tremor and fat loss

Tremor is defined as rapid oscillations of the body to produce kinetic heat (7).

A low grade tremor is a physical exertion that primarily uses fatty acids as a substrate, but, at high intensities switches primarily to the use of carbohydrates as a substrate (8).

Cold exposure and metabolic expenditure

It would appear that exposure to cold induces a greater effect as a reward response to the thermic effect produced by food (ETA) when food is ingested, where it is more significant in periods of moderate rather than high intake (9).

Studies vary depending on the degree and intensity of cold exposure and the individual tendency to compensate with metabolic or insulating changes. 

Relevance 

Some people tend to eat more when they are cold, in one test office workers at 20 degrees ate 100kcal more than workers exposed to 26 degrees (10).

Animal tests have shown that cold temperatures may make you more susceptible to eating highly palatable food (11).

On the other hand, the evidence does not deny that, although more calories are consumed after exposure to cold, on the other hand, energy consumption is increased through brown fat (12).

Conclusion

It is impossible to determine whether exposure to cold can actually have benefits for an individual. One study showed that caloric expenditure with low to moderate exposure to cold ranged from a 12% increase to a 5% decrease (13).
In obese people it is not clinically relevant, in a study of swimmers exposed to cold, an increase in GER of 950kcal and 450kcal was seen in the control group in 24hs, that is 40kcal per hour and 20kcal for the control group respectively, the energy cost of exercising is much higher (14).

While exposure to temperatures less than or equal to 15 degrees Celsius may lead to fat loss of 2.2 to 4.4kg per year due to the production of brown adipose tissue to maintain core temperature, trials to date have only lasted for days or weeks, so long-term fat loss is not known.

To date, May 2023, there is no effective cold exposure protocol specifically relevant to fat loss.