Despite what many believe about body fat, we all need a certain amount to function optimally and, like dietary fat, not all fat cells are created equal. In fact, increasing metabolically active brown fat can actually improve your physique.
A healthy body fat percentage for women is between 15-25%. This is generally comprised of belly (visceral) fat and the fat found under our skin (subcutaneous).
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White fat stores fat
White fat, or white adipose tissue (WAT), is the predominant form of fat found in the body, and is the type most closely associated with weight gain and obesity due to its role as an ‘energy storage facility’.
Each white fat cell contains a single large fat droplet, and has receptors for important hormones that regulate our metabolism, the most important of which are insulin and cortisol.
White fat cells also have important functions within our endocrine system as they produce hormones such as leptin, an important appetite-regulating hormone that controls our satiety.
However, white fat cells increase body fat levels when we consume excess calories, especially when insulin sensitivity is reduced due to a high carbohydrate and sugar-laden diet.
And excessive amounts of white fat, particularly the visceral fat located in the belly around organs and waist is closely linked lifestyle diseases like metabolic syndrome, type 2 diabetes and cardiovascular disease.
Brown boosts your metabolism
There is, however, one form of body fat that can help keep levels white fat in check. Brown fat is, like muscle tissue, metabolically active, whereas white fat is not.
This means that brown fat cells have the ability to convert ingested energy from food and stored energy from white fat cells into body heat.
To effectively perform these functions, brown fat cells have a much higher density of mitochondria – the structures within cells where the energy conversion occurs – than white fat cells.
They also contain lots of iron and have dense capillary beds for increased blood flow. This enhances nutrient delivery, which these cells convert into energy and is the reason why this fat has a brownish appearance.
Converting brown to white
It was previously thought that when the mitochondrial density of brown fat decreased as we got older, brown fat cells were converted to white fat.
However, research now indicates that this is not the case. In fact, it seems that our primary form of brown fat is more closely linked to muscle tissue than white fat.
A study published in the journal Nature showed that brown fat and muscle both originated from the same type of cells – called progenitor cells – and were merely differentiated by a particular regulator protein.
In mammals, the primary function of brown fat is to generate body heat in animals that hibernate. Newborns and infants who cannot shiver to generate body heat also have a higher proportion of brown fat cells than adults (shivering causes metabolically-active tissue – muscle and brown fat – to burn calories to produce heat). However, as we progress through childhood the amount of brown fat we carry decreases.
Scans confirm that adults still carry some degree of brown fat, mainly in their upper chest, shoulders and neck, and that certain people tend to have more.
These people are generally thinner, healthier and are more efficient at glucose metabolism, which led researchers to suggest that brown fat can help us limit the amount of energy that gets stored as white fat by increasing our metabolisms and, as such, is a suitable means to combat obesity and manage weight.
Stoking your metabolism
With that concept in mind, researchers set out to try and determine how we can best harness the metabolic power of brown fat cells.
Accordingly, a growing body of evidence is emerging that shows we have the ability to increase the amount of brown fat in our bodies. For instance, brown fat deposits tend to become more visible on scans when we’re exposed to very cold temperatures as their metabolic activity increases to produce more heat.
Studies have also shown that stimulating the production of catecholamines – hormones produced by the adrenal glands – can convert white fat cells into more beneficial brown variants.
This is a process scientists are calling ‘browning’, and these brown cells have been show to burn fat for energy in various studies.
Increasing brown fat
These results form part of a growing body of research into “beige” or “brite” (brown in white) fat – white fat that behaves like brown fat.
One of the ways scientists are trying to accelerate this process is through temperature manipulation as cold temperatures can increase brown fat activity, as well as production, while warmth has the potential to suppress it.
For example, researchers from the University of Kentucky School of Medicine took thigh fat tissue samples from 16 people after they had held an ice pack on the skin for 30 minutes. They determined the kind of fat present by checking for specific genetic markers and found elevated levels of three markers tied to beige or brown fat in samples taken during winter.
They also analysed belly fat tissue samples from 55 people, which revealed that belly fat tissue biopsied in the winter was higher in beige fat, compared to the samples taken in the warmer summer months. The researchers also found that obese people couldn’t convert their white fat to beige fat as well as slim people could.
Getting enough quality sleep is also important as healthy melatonin production has been linked to the production of brown fat, and regular exercise increases metabolic activity in brown fat.
In terms of diet, research shows that when people overeat they not only increase their total amount of white fat but the overconsumption also makes brown fat dysfunctional, which lowers its ability to burn calories.
Accordingly, when it comes to weight loss and improved overall health, it pays to not only focus on reducing the amount of white fat you’re carrying by taking steps to increase the amount and the activity of your brown fat cells.
Author: Pedro van Gaalen
When he’s not writing about sport or health and fitness, Pedro is probably out training for his next marathon or ultra-marathon. He’s worked as a fitness professional and as a marketing and comms expert. He now combines his passions in his role as managing editor at Fitness magazine.