What is brown fat?
The fat in our bodies is composed of two types of fat tissue. White fat is what we usually talk about when we refer to body fat. It stores your energy in large fat droplets around your body. While having fat deposits is useful for keeping us warm, too much white fat isn’t necessarily a good thing. Humans have evolved and developed other ways of keeping warm, making fat deposits unnecessary. Not only does too much white fat lead to obesity, it has also been linked to higher risk of heart disease, diabetes and other metabolic diseases.
Thankfully, not all fat tissue is bad. While white fat stores energy, brown fat, also known as brown adipose tissue (BAT), burns that energy in the process known as thermogenesis. Thermogenesis is essentially a process of producing heat, and it occurs in all warm-blooded animals. In fact, it is found most abundantly in hibernating animals, which allows them to survive for extended periods of time even in freezing temperatures.
Brown adipose tissue gets its name because brown adipocyte cells contain iron-rich mitochondria, which gives the tissue its reddish brown color. Because of its ability to burn calories, brown fat is often seen as a possible solution for obesity and various metabolic disorders. 
In humans, the amount of brown fat is highest when we are newborns, and as we age, the amount of brown fat decreases. It used to be thought that brown fat disappears by the time we are adults, however it turns out everyone has a certain reserve of constitutive brown fat which we have had from birth. We also have some “recruitable” brown fat, which is formed when the lack of BAT triggers a signal to recruitable fat cells, basically telling them to turn into brown fat. While researchers are still trying to understand the genetic component behind white and brown fat production, one study showed that even when mice were engineered to be born with very little brown fat, they “recruited” brown fat cells when exposed to cold. 
How can we increase the amount of brown fat in the body?
As previously mentioned, to increase the amounts of brown fat in the body, one has to cause the body to respond in a way that triggers the production of recruitable brown fat cells. Because of its potential effect in regards to treating obesity, there has been research to develop drugs to increase the amounts of brown fat. However, it’s important to keep in mind that every drug comes with a list of potential side effects, and it is always best to go the natural route.
Exposure to cold
Since the main function of brown fat is to create heat, you can trick the body into recruiting more brown fat cells by exposing yourself to cold temperatures. A 2015 study suggested that moderate cold exposure could be used as a way to robustly activate brown adipose tissue. The research showed that in healthy subjects, daily exposure to low temperature (19°C) for two hours was enough to activate brown fat, resulting in weight loss. 
You can create the necessary conditions by taking a cold bath or shower, turning down your AC setting, or simply going outside in cool weather. Additionally, you could use a cooling vest or an ice pack.
Exercise has been known to be an efficient method to burn calories for generations. However, exercise has also been shown to contribute towards the build up of brown fat cells. An animal study published in Cell Metabolism in 2015 made a connection between physical activity and brown adipose tissue. The researchers conducted practical experiments on mice and found out that exercising triggers the release of an enzyme called irisin. Irisin prompts white fat cells to convert to brown. Exercise causes a similar effect in humans. Specifically, irisin levels are increased when people do intense aerobic interval training. 
Another research from 2018 showed a consistent pattern of increased levels of a particular lipokine (fat-controlling hormone) after exercise. “This shows that these lipokines can be regulated by exercise, and it highlights a new role that brown fat could play in the metabolic benefits of exercise,” said Kristin Stanford, who led the study. 
It is advised to get 30 minutes of moderate intensity exercise at least 5 days a week. You can also combine cold exposure and physical activity by performing exercise in a cool environment.
Finding a balance can be tough, but the best way to promote brown fat activity is to avoid eating too few or too many calories. Overeating creates larger white fat deposits, while limiting the number of calories is likely to trigger “survival mode” and make your body hold on to every bit of fat.
As well as focusing on the nutritional value of your food, focus on its quality. Try to follow a balanced diet made up of whole foods. Avoid fast food and highly processed foods. Try to limit the consumption of animal fats in favor of plant oils. Include plenty of whole grains and legumes in your diet.
One of the natural enzymes that could help you increase brown fat stores is a chemical called ursolic acid. It is contained in apple skin, as well as dark fruits such as cranberries, plums and prunes. 
Ursolic acid is also found in herbs such as oregano, thyme, lavender and peppermint, so don’t be afraid to add some fresh herbs into your meal, or make a peppermint or lavender tea.
You can also help your body increase brown fat stores by eating more garlic, including turmeric in your meals and smoothies, and spicing things up with hot peppers such as cayenne, red chilies and habanero.
Last but not least, you can stimulate brown fat activity by getting adequate amounts of rest. Try to create healthy sleep habits by setting a regular sleep schedule, aiming for 7-9 hours of quality sleep every night. It would also be beneficial to create an optimal environment – a dark room, comfortable bed, and quiet surroundings. If you are a light sleeper, you might want to invest in a white noise machine to help tune out unwelcome sounds.
- Brown and beige fat in humans: thermogenic adipocytes that control energy and glucose homeostasis by Labros Sidossis and Shingo Kajimura, 2015 – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4319444/
- Brown-fat Paucity Due to Impaired BMP Signalling Induces Compensatory Browning of White Fat by Tim J Schulz, Ping Huang, Tian Lian Huang, Ruidan Xue, Lindsay E McDougall, Kristy L Townsend, Aaron M Cypess, Yuji Mishina, Emanuela Gussoni and Yu-Hua Tseng, 2013 – https://pubmed.ncbi.nlm.nih.gov/23485971/
- Brown and Beige Fat: Molecular Parts of a Thermogenic Machine by Paul Cohen and Bruce M. Spiegelman, 2015 – https://diabetes.diabetesjournals.org/content/diabetes/64/7/2346.full.pdf
- Detection and Quantitation of Circulating Human Irisin by Tandem Mass Spectrometry by Mark P. Jedrychowski, Christiane D. Wrann, Joao A. Paulo, Kaitlyn K. Gerber, John Szpyt, Matthew M. Robinson, K. Sreekumaran Nair, Steven P. Gygi, and Bruce M. Spiegelman, 2015 – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4802359/
- 12,13-diHOME: An Exercise-Induced Lipokine that Increases Skeletal Muscle Fatty Acid Uptake by Kristin I. Stanford, Matthew D. Lynes, Hirokazu Takahashi, Yu-Hua Tseng, Paul M. Coen and Laurie J. Goodyear, 2018 – https://www.cell.com/cell-metabolism/fulltext/S1550-4131(18)30241-9
- The Science of Brown Fat: Enhancing glucose metabolism and fighting diabetes by George King M.D., 2016 – https://www.psychologytoday.com/gb/blog/the-health-chart/201610/the-science-brown-fat