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Caffeine keeps your body fat warm, on top of lighting up your brain

Hot take: caffeine triggers brown fat thermogenesis via the brain

Pamela Hirschberg

Cellular Neuroscience

Rutgers University

For many people, drinking a cup of coffee in the morning is a sacred ritual. It tastes great, and it helps the morning fog to dissipate. Since it's such a big part of our daily lives, it's hard to think of caffeine as a psychoactive drug. We know plenty about the alerting qualities of caffeine on the brain, but less about caffeine's other benefits. According to a study published earlier this year by a group from La Trobe University in Australia, lead-authored by Lachlan van Schaik, caffeine increases activity in brain regions associated with brown fat thermogenesis, and increases the temperature of brown fat.

You may be asking, "what is brown fat?" Well, it's is an important part of mammalian physiology.  It exists in areas called depots near vital organs and produces heat to defend against cold temperatures. Heat production in brown fat is called "non-shivering thermogenesis" because it is different from shivering, which produces heat using the movement of your muscles.

Non-shivering thermogenesis requires a special protein found in brown fat cells. This protein adjusts the normal energy-producing chain in the mitochondria of the brown fat cells. This change causes them to produce heat instead of energy for other cellular processes. Because brown fat burns fuel to make heat independently from exercise, this tissue is a hot topic among endocrinologists  as a potential therapeutic avenue to treat type 2 diabetes and other diseases associated with obesity.

Although there have been studies in the past that measured the effects of caffeine on brown fat, this one did something a little different. The researchers wanted to be completely sure that they could attribute the effects of caffeine on brown fat to its actions on the brain. Other studies administered caffeine throughout the body, either by injection or ingestion. These researchers cut out the middleman and injected the caffeine straight into live male mouse brains.

They facilitated the injection of caffeine into the brain by surgically placing a tiny metal tube that fed into the ventricles of the brain. The caffeine could then be fed directly through this tube into the ventricles. The ventricles are where the fluid that bathes the brain moves freely, so the caffeine could potentially act on any area of the brain.

The mice used in this study were given doses of caffeine proportionate to those consumed by humans in one cup of coffee. After they injected the caffeine into the mice, the researchers measured activity of brain areas associated with brown fat thermogenesis. They did this by staining brain tissue for the presence of a specific marker for neuronal activity, then looking at it under a microscope.

The brain staining experiment revealed that several regions of the brain were activated in response to caffeine injection, including regions of a brain area called the hypothalamus. Some of these regions of the hypothalamus were previously found to play a role in the brain's control of brown fat thermogenesis.

The researchers performed other experiments to observe the brown fat response to caffeine as well. They chose the most direct measurement of brown fat heat production, which was to simply measure the temperature of the tissue. They surgically placed a tiny thermometer in the mice beneath their brown fat deposits to monitor its temperature of their tissue in real time. After just 10 minutes, they found that the brown fat got warmer in response to the caffeine. This temperature increase was independent of the overall body temperature of the mice, which is important in order to distinguish caffeine's effect on the temperature of the whole body versus just the heat production in the brown fat.

Although these results seem to indicate that caffeine ingestion helps increase heat production in brown fat, it doesn't mean you should immediately quit your workout routine and celebrate with a piping hot cup of joe. One main reason is because this study completely ignored female mice. This often happens because researchers do not want to deal with the added variable of hormonal fluctuations associated with their estrus cycles. Understanding the link between caffeine and thermogenesis in female mice will be an important follow-up to know how caffeine could potentially affect the brown fat of female mice, particularly because brown fat thermogenesis is modulated by estrogens.

Thus, the results of this study are potentially translational and valuable to healthy males of a normal weight, but the study of brown fat is very often impactful because of its therapeutic potential for diabetic or overweight men and women. Future research should focus on the effect of brain caffeine on brown fat of male and female mice, including diabetic and overweight mouse models.

Despite the caveats in these results, they did reveal that caffeine turns on brain regions that are responsible for brown fat thermogenesis, and that it may help some people burn fat. So until the next set of results come in, we can all patiently sip our coffee or tea, awaiting the heat.