Brown Fat: A Potential Target For Increased Weight Loss?

Calories-In And Calories-Out?

If you want to execute a successful fat loss plan, then there are two important things you need to consider in order to make that happen: the total number of daily calories you consume (calories in), and the total number of daily calories your body expends (calories out). Simply put, the weight changes in which your body undergoes over time, are ultimately going to be determined by this ongoing battle between the total amount of energy flowing into your body and the total amount of energy flowing out. The thing is, without knowledge of this simple energy principle, no fat loss plan implemented will ever work in your favor. You will simply end up just spinning your wheels constantly asking yourself: why am I not losing weight? Ok, so in order to actually satisfy this simple energy principle so that you can successfully lose fat over time, we need to find ways of helping you to reduce your daily energy intakes and/or by increasing your daily energy expenditures.

While the most common advice given today is still: eat less food (take fewer calories in) and/or do more exercise (more calories out), I can’t help but wonder if there is anything else you could be potentially doing to help flip this energy balance in favour of increased fat loss. Well, the good news is, there actually might be! Recently, a lot of research has emerged in the field of brown fat and how brown fat itself could prove a highly effective target for weight reduction. If this research checks out, you potentially have more tools at your disposal to help shift the balance of energy towards fat loss. Specifically, increasing energy expenditure (the calories out part). While reducing food intake and/or increasing activity levels are great tools to implement for fat reduction, it would also be nice to a have just a few more options available!  


What Is Brown Fat?

So most of us have read and learned that fat is the storage of excess energy in the body. If you consume too much food without giving your body a reason to use it (e.g. through increased exercise), over time, you will start to see some pretty unfavourable changes in the mirror. Not what we want! Well, this is only partially true. Within the body, we have two types of fat: white and brown fat. While white fat accounts for most of the fat that we have (within our muscles, around our organs, and under our skin), and is the storage unit of excess energy, our bodies also have the capacity to maintain brown fat. Some of you are probably now wondering just what exactly brown fat is? Well, unlike white fat which stores energy, brown fat actually uses energy for the production of heat. It is not only our muscles and organs which utilise energy for everyday function, brown fat also tags along for the ride. So there you have it! Having some body fat can actually help you lose more body fat over time. Sounds confusing, but it’s pretty cool! But more specifically, having more brown fat in your body, could help you get rid of the white stuff, that over time if allowed to accumulate, can give rise to an unfavourable body composition that you so desperately want to change.

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So How Does Brown Fat Work?

The problem with white fat is that it is typically considered metabolically inactive. In other words, it just does not do anything immediately useful in the body. As a result, it is simply deposited around the body, holding a store of long-term energy if the body really needs to tap into it (which in this day and age, is not all that often!). However, for most of us, especially in the western world, we are never going to really find ourselves in a situation whereby we are at risk of extreme starvation. We are always going to have access to a plentiful supply of energy-rich foods and therefore, our bodies see no reason to tap into this long-term backup energy supply. Given that we are eating more, exercising far less and buying a lot more calorie-dense foods (e.g. chips, pizzas, burgers, candies), our bodies have a constant (and often SURPLUS) influx of energy. So really, our bodies don’t really have a reason to tap into this white fat tissue. So rather than using the white fat it already has, we just give our bodies a reason to create much much more of it, continuously building up, and then dumping it around the body until one day we look at ourselves in the mirror and say: yikes! I really have to lose some weight! This weight that you notice, is the build up of this white fat tissue.  

However, this is where brown fat becomes interesting in all of this. Now from a survival perspective, brown fat is hugely important in other animals, particularly mice (as well as infants and young children), which are loaded with brown fat. The role of brown fat is all about thermoregulation (controlling your body temperature). Unlike adult humans which have fully developed mechanisms to generate heat and regulate body temperature (e.g. through repeated muscle contractions leading to shivering), infants, young children and other animals don’t have these same muscular-induced shivering mechanisms (well, at least not to the same extent as in adults). As a result, they need something else to help stabilize their body temperatures. Brown fat seems to be the primary mechanism through which this occurs. Essentially, brown fat is activated by a variety of biological goodies in your bloodstream (glucose and norepinephrine), whereby these biological goodies are than shuttled into the brown fat cells where they increase what is known as lipolysis (the breakdown of intracellular stored triglycerides into fatty acids). Subsequently, these fatty acids are than fed into the mitochondria of the brown fat cells (mitochondria are simply the small powerhouse factories for all your body’s cells) combining with specific proteins (mitochondrial brown fat uncoupling protein 1). Following this combination of fatty acids and proteins in the mitochondria of brown fat cells, heat is ultimately produced. There you have it, you stay nice and warm!

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So as you can see, while white fat is simply being lazy and storing and keeping energy all for itself, brown fat is actually using lots and lots of energy to produce body heat. Now, if you think back to the whole energy-in and energy-out principle, you can see that brown fat activity is helping to increase the ENERGY-OUT side of the equation. Assuming you keep your energy-in constant (food consumed), then increasing heat generation (through brown fat cell activity) and exercise output (more daily activity), will only serve to favour a greater shift towards energy-out (expenditure), leading to potentially greater reductions in weight.

Is This A Feasible Path Towards Weight Reduction?


1). The Cypess et al. (2015) Study

Honestly, all this sounds great on paper. Besides eating less and/or doing more exercise, having other tools at our disposal for weight loss sounds really great. The more tools we have for weight loss, the greater our weight loss efforts are likely to be. Anything we can do to shift internal energy balance in favour of increased weight loss, is hugely welcome! However, at this time, it is still all theoretical. The concept of brown fat and the potential link to weight loss in humans has not yet been fully tested. While we have a good idea of how brown fat tissue actually works in thermoregulation, the extent of their influence in metabolism and human weight loss, is still yet to be fully determined.

One of the problems we have is that humans have much less whole body brown fat tissue than that of rodents (Townsend and Tseng, 2015). Humans simply don’t need it to the same extents for internal body temperature regulation. Why? We just have other thermoregulatory mechanisms at play! This begs the question: even if we can make full use of the little brown fat we do have, will this result in energy utilisation within the body to great enough extents to allow for a sizeable impact on weight loss? A recent study by Cypess et al. (2015) might shed some light on this question. Cypess et al. looked at the influence of increased activation of human brown fat tissue on the resting metabolic rates (RMR) of 20 healthy male participants. In this study, a placebo or single-dose of 200mg of beta 3-receptor agonist drug (mirabegron*) was applied in order to stimulate the activity of brown fat tissue. Moreover, the activity of brown fat tissue was measured by degree of uptake of a F-fluorodeoxyglucose through combined positron emission tomography and computed tomography. Furthermore, the effect of increased brown fat tissue activation by mirabegron on RMR and subsequently body fat, was also investigated.

  • The beta 3-receptor is highly expressed on brown fat tissues in relation to other beta-receptors, with mirabegron being the first agonist drug to display a high-degree of binding affinity to beta-3 receptor over other beta-receptors.


Cypess et al. (2015) Study Results:

The group found that application of mirabegron in the male participants compared to placebo, led to a significantly greater increase in brown fat tissue activity. In other tissues investigated (heart, liver, skeletal, white fat), there were no significant differences in brown fat activity between placebo and mirabegron application.

There was a positive correlation between the extent of brown fat tissue activity and the increase in RMR in response to mirabegron application (approx. 203 kcal/day). However, no correlation was observed with placebo administration.

There was a positive correlation between changes in RMR and body fat mass in response to mirabegron, but not placebo administration. 



Cypess et al. (2015) Study Conclusions

When you look at the results obtained from this study, you can see some potentially promising avenues for the use of brown fat tissue in weight loss. By activation of brown fat tissue, the increase in their activity seems to lead to significant increases in RMR, which of course helps to increase your daily calorie expenditures. Subsequently, the increase in daily calorie expenditures can help lead to reductions in body fat mass as shown in this study. Sounds great! It seems we have just found a way of being able to shift our internal energy balance in favour of fat loss!

But, there are a few things to take into account with this study before getting too excited: Beta-3 receptors are found not only in brown fat tissue, but also in the gallbladder and urinary bladder tissues. We don’t know what the potential (if any) long-term consequences could be for these other tissues if these beta-3 receptors are also stimulated. We might not want to be messing with beta-3-receptors if some people have already compromised gallbladder and urinary bladder functions! Furthermore, even though mirabegron was highly selective to the beta-3-receptor, it still can act on other beta-receptors throughout the body. Since beta-receptors play a diverse role in modulating cardiac (heart), smooth muscle function, neurotransmitter release and metabolic function, the potential weight loss advantages through activation of these brown fat cells, might not be worth the potential cost to the rest of the body! Currently, there is just nothing available which can ONLY activate the beta-3 brown fat cell receptors.

Another problem with this study was that changes in RMR were only observed after a single acute dose of 200mg mirabegron. Therefore, the potential long-term effects on metabolic function from chronic treatment are not known. Although activation of brown fat tissue resulted in a peak expenditure of approx. 200 kcal/day (average), this was only the peak and not that maintained through the entire day. As a result, the potential maximum weight loss that could be achieved say in a year, would likely be far less than hoped. Finally, with a small study sample, of only men and healthy volunteers, it makes it difficult to assess how these changes on body fat and metabolism might change in regards to difficult populations and in different weight stages. This study might be more relevant in those that are already overweight or obese!


2). The Takeshi et al. (2013) Study:

In this study, Takeshi et al. investigated the influence of brown fat tissue activity on weight reduction in 51 healthy male volunteers in response to 1) cold exposure at 17 degrees for 2 hours every day (over a 6-week period) and 2) daily ingestion of 9mg capsinoids* (over a 6-week period). Both groups were compared against controls: either no cold exposure (continued normal daily activities without exposure) or placebo (in place of capsinoids).

*capsinoids are substances that naturally occur in chilli peppers.


Takeshi et al. (2013) Cold Exposure And Capsinoid Ingestion Results:

After a 6-week period to cold exposure and capsinoid ingestion, there was a significant increase in brown fat tissue activation in participants.

After a 6-week period, there was a significant reduction in body fat mass (but not fat-free mass or body weight) in the cold-group and capsinoid-group compared with the control groups

After a 6-week period, there was a significant increase in cold-induced thermogenesis in the cold group compared with the control groups.

The increase in cold-induced thermogenesis was strongly correlated with an increase in brown fat tissue activity and with a decrease in body fat mass


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Takeshi et al. (2013) Study Conclusions:

Again, this is an interesting study which reveals for the potential for brown fat tissue activation in possible weight reduction. In both cases, cold and capsinoid-mediated activation of brown fat tissue led to significant increases in reductions in body fat compared with controls.


Closing Remarks: Does The Future Of Weight Loss Lie With Brown Fat Activation?

Looking at the current research, it is clear that brown fat tissue could play an exciting role in providing a target for potential weight reduction in humans. Given the role played by brown fat tissue in heat generation, it is highly possible that this mechanism could be exploited in the future to provide a novel anti-obesity treatment. However, there are still a few questions to think about before really getting too excited about brown fat tissue and its potential role in weight loss therapies. While we do know that brown fat tissue is abundant in infants, young children and rodents, you have to ask the question: why is brown fat tissue not found to the same extent in adult humans? Given that adults have fully fledged mechanisms at work already to regulate body temperature, could there be any potential hidden side-effects to artificially increasing brown fat tissue in this group? If for instance brown fat tissue activity is increased in adults, could there possibly be any compensatory metabolic mechanisms activated to counteract this new heightened brown fat activity? (e.g. an increase in energy consumption to help offset the increase in energy from enhanced brown fat tissue activity? If so, could that actually make weight loss even harder for people over the longer term?). Given that these studies only investigated the metabolic effects of brown fat tissue activation acutely and in healthy participants, more data is needed over the longer term and in groups of different body weights to be able to make more definite conclusions over the metabolic impact of brown fat tissue activation in humans.


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