This piece was written by one of our contributors; medical student and MSc in public health and clinical nutrition graduate – Rebecca Fox
Did you know? There are different types of body fat (also referred to as adipose tissue) within all of us; each with specific functions and characteristics.
White and brown fat constitute the two main types of fat, with their main differences being:
White Fat
White fat is the more common type of tissue we immediately think about when someone says “body fat”. Its main functions are to store excess energy that we consume in our diet, as well as provide a form of insulation to keep us warm (1). While we all need some body fat, having too much of it isn’t necessarily a good thing- particularly if it accumulates around our organs (otherwise called “visceral fat”) (2, 3). The amount of white fat we have increases if we take in more calories than we expend and can lead to conditions such as obesity.
Brown Fat
Brown fat, on the other hand is a type of body fat with a special function. It is largely located around many of our vital organs, large blood vessels, and underneath the skin surrounding our neck and chest (4). Previously, it was thought that only babies had brown fat and that it disappeared by adulthood. However, more recently, it has been discovered that even adults have small amounts of brown fat leftover (5).
What makes brown fat so special is its function: it produces heat through a method called “non-shivering thermogenesis”(6). Normally, we shiver to produce heat when we’re cold, but in the case of brown fat, it contains lots of mitochondria (7). In fact, the high amounts of mitochondria are what actually gives brown fat its colour when compared to white fat. In other cells of our body, mitochondria work to make energy for our body to use in the form of ATP. However, in brown fat, there is a special protein in its cell membranes called uncoupling protein-1 (UCP-1) that works to prevent the tissue from making usable energy for the body, and instead uses available energy to make heat(6, 8). Therefore, this process allows brown fat to expend more energy that may be important for a variety of reasons, particularly for weight loss.
Current Research
So we know that brown fat and white fat have different functions, but what are the implications? Well, there is a lot of buzz surrounding the potential for brown fat to be utilized in therapies for conditions such as type 2 diabetes and obesity in which excess body weight is a concern.
One of the interesting things about brown fat is that there seems to be both a genetic component and environmental aspects that dictate how much of it a person has(7). Certain people have greater amounts of brown fat that sticks around until adulthood. However, it appears that there is also some fat present within muscle and white fat that can turn into brown fat under the right conditions. This type of fat is referred to as “beige fat” and appears to contain that UCP-1 protein mentioned earlier- but in an inactive form. Much research has focused on what environmental conditions allow beige fat to turn into brown fat in the process referred to as “brown fat induction” or “browning” (9).
Two key areas of research into this include:
- Cold Exposure
There have been a number of studies performed both in animals and humans that have shown that exposure to cold temperatures may be able to increase the quantity of active brown fat we have (7, 10).
One study in particular found that in healthy people who were exposed to 19C degree temperatures for two hours per day, higher amounts of brown fat was activated – leading to minor weight loss and improved insulin sensitivity (11). Similarly, in a smaller study performed in healthy men who were exposed to 10C for 2 hours per day for 4 weeks, there was an increase in both the amount and metabolic activity of the participant’s brown fat (12). This suggests that there may be some ability for healthy individuals to increase both how active their existing brown fat is, as well as increase the overall quantity of it. However, it is important to note that these studies were both performed in men using relatively small sample sizes, so these results may not necessarily be definitive or repeatable in other groups of people.
- Exercise
Another potential way in which we might be able to induce brown fat is through exercise. One study found that, in mice, aerobic exercise appeared to be able to turn some white fat into brown fat (13). However, exercise-induced fat “browning” in humans is less clear.
There have been multiple studies performed using a variety of exercise techniques (strength, aerobic etc), as well as exercise combined with cold temperature exposure. While there does appear to be some positive results increasing the amount of brown fat activity, these human results aren’t clear enough to be able to draw any definite conclusions(14).
However, a little exercise is good for everyone. The NHS recommends that adults age 19-64 do some form of physical activity each day, aiming for at least 150 minutes of moderate activity or 75 minutes of vigorous activity per week. So, even if you may not be affecting your brown fat, there are certainly other benefits to exercising.
Key Points
- White fat and brown fat have different functions and tend to be located on different parts of the body
- We have more brown fat as infants, and it lessens as we age
- Having more brown fat may lead to health benefits such as weight loss, as well as have potential effects on improving insulin sensitivity and glucose metabolism
- Some fat is “beige” and potentially has the ability to turn into brown fat
- Exercise and cold exposure appear to be two main conditions that can increase the amount of brown fat we have- although current research isn’t at the stage where definitive recommendations can be given.
References
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(3) Siddiqui NI, Soni A, Shoeb M, Bose S, Wadhwani R. Evaluation of the Discriminatory Abilities of Anthropometric Indices of Obesity in Prediction of Important Body Composition Parameters of Central Obesity. Journal of Clinical & Diagnostic Research. 2019;13(2).
(4) Din MU, Saari T, Raiko J, Kudomi N, Maurer SF, Lahesmaa M, et al. Postprandial oxidative metabolism of human brown fat indicates thermogenesis. Cell metabolism. 2018;28(2):207-16. e3.
(5) Marlatt KL, Ravussin E. Brown Adipose Tissue: an Update on Recent Findings. Current obesity reports. 2017;6(4):389-96.
(6) Cannon B, Nedergaard J. Brown adipose tissue: function and physiological significance. Physiological reviews. 2004;84(1):277-359.
(7) Kim SH, Plutzky J. Brown fat and browning for the treatment of obesity and related metabolic disorders. Diabetes & metabolism journal. 2016;40(1):12-21.
(8) Heaton GM, Wagenvoord RJ, Kemp Jr A, Nicholls DG. brown‐adipose‐tissue mitochondria: photoaffinity labelling of the regulatory site of energy dissipation. European Journal of Biochemistry. 1978;82(2):515-21.
(9) Wu J, Boström P, Sparks LM, Ye L, Choi JH, Giang AH, et al. Beige adipocytes are a distinct type of thermogenic fat cell in mouse and human. Cell. 2012;150(2):366-76.
(10) Yao L, Cui X, Chen Q, Yang X, Fang F, Zhang J, et al. Cold-inducible SIRT6 regulates thermogenesis of brown and beige fat. Cell reports. 2017;20(3):641-54.
(11) Lee P, Smith S, Linderman J, Courville AB, Brychta RJ, Dieckmann W, et al. Temperature-acclimated brown adipose tissue modulates insulin sensitivity in humans. Diabetes. 2014;63(11):3686-98.
(12) Blondin DP, Labbé SM, Tingelstad HC, Noll C, Kunach M, Phoenix S, et al. Increased Brown Adipose Tissue Oxidative Capacity in Cold-Acclimated Humans. The Journal of Clinical Endocrinology & Metabolism. 2014;99(3):E438-E46.
(13) Boström P, Wu J, Jedrychowski MP, Korde A, Ye L, Lo JC, et al. A PGC1-α-dependent myokine that drives brown-fat-like development of white fat and thermogenesis. Nature. 2012;481(7382):463-8.
(14) Dewal RS, Stanford KI. Effects of exercise on brown and beige adipocytes. Biochimica et Biophysica Acta (BBA)-Molecular and Cell Biology of Lipids. 2019;1864(1):71-8.
