Monday, January 24

How brown body fat differs from white (and why isn’t all of it bad)


When we think of adipose tissue, the unpopular “love handles” or “tires” inevitably come to mind, which today we perceive as a problem.

However, we must bear in mind that the ability to store the surplus energy ingested as fat deposits has allowed our species to survive. In other words, there is a lot to be thankful for.

The main fat reservoir in our body is white adipose tissue, but there is also brown adipose tissue.

The latter has an opposite function, since allows us to “burn” stored fat, dissipating energy as heat. That makes it an interesting target in the fight against obesity and its complications.

weighing machine
Our sedentary lifestyle causes us to accumulate fat, but some of it could help us lose weight, according to the latest research. (Photo: Getty Images)

White adipose tissue: a reserve for times of need

Food contains nutrients that provide us with the energy (calories) that our body needs to function. If we eat more calories than we expend, we do not waste them, but we convert them very efficiently into fat (triacylglycerides) that we store in cells, adipocytes, that form white adipose tissue.

This fat reservoir remains available to deal with shortages of food, in which we can mobilize the stored triacylglycerides to obtain the energy we need.

That is why fat provides an evolutionary advantage. Or rather it contributed until recently. Because at the present time, and unlike what has been happening throughout thousands of years of evolution, we find ourselves facing a quite different situation.

evolution and obesity
The surplus of ingested energy has allowed our species to survive, but our way of life is turning obesity into a public health problem. (Photo: Getty Images)

At this time, the majority of individuals of our species have at their disposal a wide range of food, some excessively caloric.

If we add to the overflowing refrigerators and pantries that our lifestyle is increasingly sedentary, the immediate consequence is that we accumulate excess fat and we get fat.

Subcutaneous fat —That is, that of love handles— most characteristic of women, it is the least problematic. The greatest health risk is associated with visceral fat, which is the one that is deposited surrounding organs such as the liver, heart or intestines.

It is also important to note that adipose tissue not only serves as an energy reservoir. White adipocytes are capable of producing and releasing into the blood bioactive substances known as adipocytokines, with an important regulatory function of metabolism.

The problem comes when we accumulate too much fat in our adipocytes, because at that moment the production of adipocytokines is deregulated. As a consequence, inflammatory processes increase and insulin resistance, which are the trigger for various pathologies.

In short, the accumulation of body fat in the form of being overweight or obese has reached pandemic dimensions today, and are associated with cardiovascular diseases and a long list of pathologies, including different types of cancer and, even, an increased risk of cognitive damage.

donuts
Ultra-processed foods, eaten in excess, negatively affect our body composition. (Photo: Getty Images)

Brown adipose: the tissue capable of burning fat

Although white adipose tissue is the most abundant, there is another type of adipose tissue, brown. It is distinguished because, in response to cold and other stimuli, it mobilizes fat reserves and releases energy in the form of heat.

The process is known as adaptive thermogenesis, and it is very useful for maintaining body temperature in animals, including hibernating ones.

In addition, in small mammals, adaptive thermogenesis is also triggered by the intake of high-calorie diets, which helps them maintain body weight.

In the case of humans, for many years it was thought that brown adipose tissue was important in newborns to regulate body temperature, but that it disappeared in adults.

The surprise came a little over a decade ago, when it was described that humans maintain brown adipose tissue in adulthood which is capable of being activated to generate heat, using fatty acids and glucose.

This discovery promoted the appearance of projects aimed at identifying different ways to activate thermogenesis in brown adipose tissue to lose weight, improve cardiovascular health and stop diabetes.

One of them was the European DIABAT project, which was developed between 2011 and 2015, in which research centers from 12 European countries participated, including our Nutrigenomics and Obesity group at the University of the Balearic Islands.

Research continues to advance, and there is multiple evidence pointing to the benefits of brown fat. For example, it has recently been published that the presence of brown adipose tissue is related to a lower cardiovascular risk. And that could mitigate the complications associated with obesity, such as diabetes, hypertension or high levels of lipids in the blood.

Obesity
Brown adipose tissue could be activated in our favor to burn fat, either with exercise, medication or cold. (Photo: Getty Images)

What if we could turn white fat to brown?

Although the ideal is not to accumulate excess fat, the good news is that the deposits of white fat can turn into what has come to be considered a third type of fat, beige fat.

The transformation is part of a process known as brownization. It is interesting because beige adipocytes are a type of cell similar to brown adipocytes. Like them, they express the protein UCP1 or thermogenin, and therefore can carry out thermogenesis. Of course, they are located within the white adipose tissue.

Brownization of white adipose tissue can be induced with appropriate stimuli, such as exposure to cold. But also with drugs, with certain nutrients, and even with physical exercise.

This possibility is interesting because the conversion of white fat into beige fat would enhance the elimination of circulating lipids and glucose. And by increasing energy expenditure in this way, we would contribute to maintaining body weight and metabolic health.

It seems indisputable that we are facing a very powerful weapon to combat the global epidemic of obesity and diabetes.

* Paula Oliver Vara is Professor of Biochemistry and Molecular Biology (UIB, CIBEROBN, IdISBa, University of the Balearic Islands).

This article was originally published on The Conversation and is reproduced under the Creative Commons license. Click here to read the original note.


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