Humans have two main types of body fat—brown and white. White fat, or white adipose tissue, is the fat that accumulates over time when we eat too much junk food. Its main function is to store excess energy (calories). This is the body fat that most of us are trying to shed. Brown fat, on the other hand, is the fat we want.
The main function of brown fat, also called brown adipose tissues (BAT), is to burn energy as a means of generating heat when exposed to cold temperatures. For the longest time, BAT was thought to only exist in newborn and hibernating mammals, as it helps them maintain their body temperature. Newborn humans are 5% brown fat, which makes sense, as they suddenly go from their mother’s warm womb, to a much colder environment (especially before modern heating systems). Without brown fat, being born would feel worse than leaving a warm bed on a cold morning—a feeling that all of us dread. After infancy, however, it was thought that BAT dissipated as our metabolic rate increased, our muscles grew so that we could shiver, and our white “baby” fat started to accumulate. At least that’s what we thought…until recently.
About a decade ago, oncologists using PET scans (an imaging technique used to observe metabolic processes) noted metabolically active tissue in the upper chest and neck regions of adult patients. Thinking it could be cancer, further imaging was ordered. But this revealed that it was just body fat. Then, some radiologists noted that these pockets of metabolically active tissue were more common during the colder winter months. This led to a number of studies that confirmed what was suspected—the metabolically active tissue located in the upper chest and neck areas of these adult patients was actually brown fat (1-4).
Why does this matter? Well, given that BAT is metabolically active (it burns energy), there have been some interesting observations as it pertains to body weight. Early studies found that the amount of BAT was inversely associated with body weight (2-3). In other words, people with more BAT tended to be leaner, whereas people with less BAT tended to be heavier. In addition, it was found that higher amounts of BAT were associated with improved metabolic parameters, including: body fat, abdominal fat, cholesterol levels, and blood sugar regulation (5-6).
Although the impact of BAT on body weight and metabolic health needs to be studied further, having more BAT does appear to be a good thing. And guess what? There are some ways that we can increase the amount and/or activity of BAT. Here’s what we know so far:
Cold Exposure
The amount of BAT we have is inversely associated with outside temperature (3). Studies also show that we can significantly increase BAT through acute cold exposure (2;6-9). These studies exposed volunteers to cooler temperature (not cold enough to start shivering, as that would lead to muscles burning energy), which were typically between 50-60 degrees Fahrenheit. After a week or two of daily cold exposure (only a couple hours per day), participants showed significant increases in BAT volume and activity. They also acclimated to these cooler temperatures and by the end of the study participants reported feeling more comfortable in the cold, judged their environment to be warmer compared to when they started, and reported less shivering with colder temperatures (8). In one study, participants with more BAT saw a 400-calorie increase in their daily energy expenditure when exposed to cool temperatures (9). A 500-calorie daily deficit is typically recommended for long-term, sustained, weight loss. So, in theory, the increase calorie burn from BAT, could potentially lead to weight loss, or at least prevent weight gain. Unfortunately, no long-term studies have tested this. It is possible that our bodies would compensate for this extra calorie burn by storing more white fat, or by increasing our appetite. But with what we know now, it may be worth turning the heat down a little this winter. If anything, it will reduce your energy bill.
Spicy Food
Instead of turning down the heat, you could turn it up—when you’re eating, that is. Capsaicin, the compound that gives chili peppers their heat, has been shown to boost energy expenditure (10). Some recent studies suggest that this increased calorie burn may be due to the activation of BAT (11-12). Although spicy foods may cause gastrointestinal issues for some, those who can tolerate the heat or enjoy spicy foods should load up on them, as they may help you keep off some unwanted pounds. Just make sure to use a little common sense. Buffalo wings, or a gigantic plate of nachos with a few jalapenos, will do more harm than good. Healthy dishes, on the other hand, with some added red pepper flakes, cayenne pepper, or fresh jalapenos would be great options. Certain ethnic foods, such as Thai or Indian, can also provide a variety of dishes that are both healthy and spicy.
Foods Rich in Arginine
For adults, arginine, also known as L-arginine, is a non-essential amino acid (our body can make it from other amino acids). You’ll often see it sold as a dietary or exercise supplement, since it can increase blood flow and may increase levels of growth hormone. Rodent studies suggest that arginine can boost BAT growth, but there isn’t any human data to back this up (at least none that I’m aware of) (13-14). Since most foods high in arginine are good for our overall health, it can’t hurt to include the following arginine-rich foods in our diet: Sesame seeds, pumpkin and squash seeds, sunflower seeds, hemp seeds, soy products, walnuts, and peanuts.
Exercise
The effect that exercise has on BAT is not entirely clear. There’s some early evidence suggesting that exercise may boost a variety of compounds in our body that encourage the “browning” of white fat into something called beige fat (15-18). As its name implies, beige fat falls somewhere between white and brown fat, in terms of its metabolic function. It is metabolically active (burns calories), but to a lesser extent than brown fat. If exercise can indeed convert white fat (which we don’t want) into beige fat (which is better), then add that to the long list of reasons why exercise is good for us.
Summary
Boosting BAT is not going to cure our obesity epidemic, but having more is associated with better metabolic health. It’s not unreasonable to say that boosting BAT may lead to a small reduction in body weight, or potentially help prevent weight gain, but there’s not any long-term data to back that up. Drugs or supplements that claim to boost BAT should be avoided, as they’re likely ineffective, unhealthy, or both. Natural ways to boost BAT should be encouraged, as these have little, if any, harmful side effects, and are good for our overall health. So, this winter, turn down the thermostat at night. Go for a walk or run outside, rather than using an indoor treadmill (just don’t slip on ice). Or give winter sports a try, such as snowshoeing, ice skating, skiing, or cross-country skiing. Then come inside and snack on some spicy roasted pumpkin seeds. Do these things to boost your BAT, and it may help you lose some unwanted (white) fat.
Peace, love, health
References:
- Unexpected evidence for active brown adipose tissue in adult humans
- Cold-activated brown adipose tissue in healthy men.
- Identification and importance of brown adipose tissue in adult humans.
- Functional Brown Adipose Tissue in Healthy Adults
- Impact of brown adipose tissue on body fatness and glucose metabolism in healthy humans
- Short-term Cold Acclimation Recruits Brown Adipose Tissue in Obese Humans.
- Increased brown adipose tissue oxidative capacity in cold-acclimated humans.
- Cold acclimation recruits human brown fat and increases nonshivering thermogenesis.
- Brown adipose tissue, whole-body energy expenditure, and thermogenesis in healthy adult men.
- Acute effects of capsaicin on energy expenditure and fat oxidation in negative energy balance.
- Nonpungent capsaicin analogs (capsinoids) increase energy expenditure through the activation of brown adipose tissue in humans.
- Capsinoids and related food ingredients activating brown fat thermogenesis and reducing body fat in humans.
- Regulation of brown adipose tissue development and white fat reduction by L-arginine.
- Beneficial effects of L-arginine on reducing obesity: potential mechanisms and important implications for human health.
- Exercise Effects on White Adipose Tissue: Beiging and Metabolic Adaptations
- Brown and beige fat: development, function and therapeutic potential
- The effects of acute and chronic exercise on PGC-1α, irisin and browning of subcutaneous adipose tissue in humans
- FNDC5 and irisin in humans: I. Predictors of circulating concentrations in serum and plasma and II. mRNA expression and circulating concentrations in response to weight loss and exercise
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