Unlike white fat, brown fat burns calories and produces heat when the body is cold.
With the arrival of longer nights, falling leaves and frost covering the outside world at this time of year in the Northern Hemisphere, many are tempted to turn up the thermostat.
When leaving the house, they wear a scarf and hat, and layer their clothing to keep warm. However, feeling cold and uncomfortable could be the key to improve health and even lose weight.
The reason lies in a special type of fat called brown fat. Unlike white fat, which accumulates on the thighs, waist and hips, brown fat burns calories and transforms them into heat when the body faces the cold.
Some experts believe that, if activated correctly, it could help with weight loss. Theoretically, just take a cold shower or consume spicy foods and caffeine to activate it.
But before jumping into an ice-cold lake or drinking your fourth cup of coffee, it’s worth analyzing whether the interest surrounding brown fat really makes sense.
How is brown fat different?
At birth, we all have abundant reserves of brown fat, which function as an internal heater. Babies don’t have enough muscle mass to shiver, so they rely on brown fat to convert sugars and fats into heat.
Brown fat cells have a very high number of mitochondria — the energy factories inside the cells. But unlike normal mitochondria, which produce adenosine triphosphate (ATP)—the energy currency used by the body—the mitochondria in brown fat cells contain a protein called thermogeninor UCP1, which transforms calories directly into heat.
“When stimulated, brown fat has the capacity to produce 300 times more heat per unit mass than any other tissue or organ in the body”, says Michael Symonds, professor of developmental physiology at the University of Nottingham, in the United Kingdom.
Most of what is known about brown fat comes from studies of small mammals, such as mice and rats. These rodents have large reserves of fat, which keep them warm during the winter, when they hibernate.
“For our ancestors, or for small animals like mice, cold was a threat to survivalso it was advantageous to have a fat capable of transforming energy into heat”, says Paul Cohen, associate professor at The Rockefeller University, in New York (USA), specialist in molecular metabolism.
Decades of research show that, at least in rats, brown fat consumes sugars and fats present in the bloodstream. It also appears to protect animals from obesity and weight-related metabolic diseases such as diabetes and heart problems.
Brown fat in adults
Adult humans, however, have found other ways to stay warm—turning on the heat, wrapping themselves in thick blankets, or wearing warmer coats. Therefore, it was believed that brown fat practically disappeared after pubertybeing replaced by the white fat that accumulates on the thighs and with which we are all familiar.
This led many scientists to conclude that brown fat had no relevant role in health beyond childhood. This perception changed in 2009, when researchers from Finland and Sweden showed that adults still have brown fat and that, at temperatures below 16 ºC, it becomes activated, starting absorb glucose and fats from the bloodstream.
Furthermore, there was a clear correlation between body weight and brown fat stores: thinner individuals had more, while people with obesity had less. Those with more brown fat also had higher metabolic rates in the cold, suggesting that brown fat could be a target in the treatment of obesity.
The field gained momentum in 2021 with a study by Cohen and colleagues at Rockefeller University. The team analyzed positron emission tomography (PET) scans of more than 52,000 people. Comparing individuals with no detectable brown fat to those who had brown fat, researchers found that rates of type 2 diabetes, heart disease, stroke and hypertension were much less common among those with brown fat.
They also found that thinner people were more likely to have brown adipose tissue than obese individuals.
Furthermore, people with greater brown fat reserves had lower levels of glucose and triglycerides in the bloodstream, better insulin sensitivity and greater amounts of the so-called “good” cholesterol, high-density lipoprotein (HDL), all signs of healthy metabolism.
Can brown fat help you lose weight?
It is not yet clear whether brown fat is responsible for the observed health benefits. In practice, our bodies are too large and contain too little brown fat to burn white fat in quantities capable of significantly reducing weight. Most adults only have between 0.02g and 300g, or less than 0.5% of their total body mass.
“While white fat has an almost unlimited capacity for expansion — there are people with more than 100kg of white fat — brown fat is probably no more than a few hundred grams“, says Cohen, from Rockefeller University.
However, even if brown fat doesn’t help you lose weight, it can still bring health benefits. It can improve metabolic health — the body’s ability to process and use energy from food efficiently, for example. People with compromised metabolism cannot eliminate glucose from the blood quickly, increasing the risk of type 2 diabetes. Brown fat may act by absorbing glucose from the bloodstream or secreting hormones that regulate insulin sensitivity.
“In terms of total body energy expenditure, it probably doesn’t play as big a role in humans as it does in mice,” says Cohen. “So my personal impression, based on the data, is that brown fat activation will not be a good method to treat obesity or lose significant amounts of weight.”
“The data, however, indicates that activating brown fat can lower glucose and improve metabolic health. So I believe that if there is therapeutic potential, it will be more relevant to treat obesity complications and aging than to treat obesity itself.”
But how to activate brown fat and take advantage of the “superpowers” it may or may not offer? One way is expose yourself to the coldhowever uncomfortable it may be. Think ice baths, cold water swimming, or cryotherapy chambers — equipment that subjects the body to extremely low temperatures for 1 to 3 minutes to promote well-being and recovery. The heat shock triggers the fight or flight response, releasing norepinephrine, which binds to brown fat cells and “activates” them.
So are there other ways to boost brown fat without facing extreme cold?
Research suggests that and caffeineespecially coffee, can activate brown fat by stimulating glucose burning and heat production. Other scientists, however, claim that it would take about 100 cups of coffee per day to achieve significant effects; an unfeasible amount, even for regular consumers.
to capsaicin, compound present in peppershas also been shown to activate brown fat in mice, and there is evidence that the effect may occur in humans. In one study, ten men took capsaicin capsules daily for six weeks. At the end of the period, those who ingested the capsules showed greater activation of brown fat when exposed to cold than at the beginning of the experiment.
The question, then, is whether we should turn off the heating and face low temperatures more often. Possibly, although there are more effective measures to improve health. Cohen points out that maintain a healthy diet For the heart, exercising regularly, controlling cholesterol, blood pressure and glucose, as well as staying close to the ideal weight, continue to be priorities.
