We often hear about fat in our foods -- good fats, bad fats, fake fats. And the debate has been raging for decades over which fats are good for what and whether fat intake actually makes us fat. Everyone seems to know where the Academy of Nutrition and Dietetics and Gary Taubes stand on the issue, and the subject of dietary fats in the media is enough to make one’s head spin. Although the debate continues over whether fats are simply a highly concentrated source of calories or an energy source preferable to even glucose, we seem to understand the basic biochemical mechanisms of fat metabolism and fat storage in humans. But relatively little is known about the types of fat tissues found in our bodies and their various functions.
BAT vs WAT
Not long ago, it was discovered there are different types of fat cells within body tissue: brown and white adipose. Brown is referred to as such because of the actual hue these cells have due to their higher concentration of mitochondria and thus iron content. Most fat tissues found in human adults is white adipose (WAT), serving as sites for energy (fat) storage and endocrine activity that modulates whole-body metabolism including insulin response. Brown adipose tissue (BAT) conversely, is known for its energy-producing capability, termed thermogenesis. This is vital to mammals in order to maintain a normal body temperature higher than most ambient temperatures. This is mediated by the expression of a tissue-specific uncoupling protein (UCP1) that instigates the uncoupling of ATP production and substrate oxidation.
Using novel PET/CT scanning methods in the early 2000s, researchers found significantly more brown adipose tissue (BAT) distributed throughout adult human body tissue than had been previously understood. In fact, back in the 1970’s when seminal experiments were conducted with BAT, it was thought it was only found to any significant extent in babies and small mammals (rodents) as an evolutionary artifact useful in keeping them warm. Studies conducted in the last two decades have shown most adult human BAT appears interspersed within WAT, appearing less brown, so they term it “beige” or “brite”. Unfortunately, there is still a paucity of research with humans and BAT (most still has started with rodents as study subjects), but the recent findings in this area suggest we should really be looking at harnessing BAT functionality as a potential therapeutic target to combat the obesity epidemic.
What does the research say?
A review published in December 2017: “Brown Adipose Tissue: an Update on Recent Findings”, describes BAT induction versus BAT activation. The first, induction, is referred to in the literature as “beiging” of WAT by way of cold exposure. In this case, studies have artificially induced UCP expression, mostly in rodents with lower amounts of BAT, resulting in an increase of “brown-like” WAT that has similar thermogenic properties to BAT. These findings correlated to reduced body fat and complications related to obesity. BAT thermogenesis activation has been shown to be tied to a variety of pathological and physiological factors as well. Humans with higher BAT concentration tend to be younger, female, live in colder climates, and have lower fat mass. This latter descriptor of BAT activation has gotten the most attention in recent years due to its potential for ameliorating risk factors associated with cardiovascular disease such as poor lipid profile and insulin dysregulation. Many studies have focused on metabolic activity using controlled cold exposure in order to stimulate BAT activation.
One such study looked at glucose uptake and fatty acid metabolism in adults with type 2 diabetes and found the main substrate for activating the BAT to be fatty acids from intracellular triglycerides, thereby reducing fat storage. Another study showed plasma-derived glucose (30%) and free fatty acids (70%) were the primary substrates when cold exposure increased study participants’ resting metabolism by 14%. In a brief 10-day study where overweight men with type 2 diabetes were put through a cold acclimation protocol, researchers found intensified BAT activity and overall improvement in insulin sensitivity. Yet another study that used a simple cold acclimation procedure of having healthy study participants sleep in a 66°F room with light clothing found improvements in postprandial insulin sensitivity.
The role of food and nutrients in “beiging” our WAT
In order to increase concentration and activate BAT, otherwise known as “beiging” of our WAT, most research has studied the effects of cold exposure. Consuming certain foods can produce a similar effect. We historically have referred to this as thermogenic effect of food or TEF, without quite understanding the mechanism behind the phenomenon.
A recent review of the beiging process highlights pharmacological targets, as well as natural agents that may play a role in enhancing metabolic activity through thermogenesis. Many of these include the constituents found in plants and foods long thought to aid in fat-burning in humans. Here is a short list of the research that associates these compounds with induction or activation of brown fat. Note, once again, most of this research was conducted with rodents as subjects:
- Capsaicin or chili pepper: “Capsaicin induces browning of white adipose tissue and counters obesity by activating TRPV1 channel‐dependent mechanisms” (2016);
- Green tea: “A polyphenolic extract from green tea leaves activates fat browning in high-fat-diet-induced obese mice” (2017);
- Resveratrol; “Resveratrol enhances brown adipocyte formation and function by activating AMP-activated protein kinase (AMPK) α1 in mice fed high-fat diet” (2017);
- Quercetin: “A combination of resveratrol and quercetin induces browning in white adipose tissue of rats fed an obesogenic diet” (2016);
- Berberine: “Berberine activates thermogenesis in white and brown adipose tissue” (2014); (**maybe make a link to the other blog post about berberine?)
- Ginsenoside, the active constituent found in ginseng (plant genus Panax) varietals: “Ginsenoside Rb1 promotes browning through regulation of PPARγ in 3T3-L1 adipocytes.” (2015);
- Menthol found in peppermint: “Chronic l-menthol-induced browning of white adipose tissue hypothesis: A putative therapeutic regime for combating obesity and improving metabolic health” (2016);
- Caffeine: “Tea catechin and caffeine activate brown adipose tissue and increase cold-induced thermogenic capacity in humans.” (2017);
- Cinnamon: “Cinnamon induces browning in subcutaneous adipocytes” (2017);
- Ginger: “Gingerenone A, a polyphenol present in ginger, suppresses obesity and adipose tissue inflammation in high-fat diet-fed mice” (2017);
- Curcumin, commonly known as turmeric; “Curcumin promotes browning of white adipose tissue in a norepinephrine-dependent way” (2015);
- Foods containing L-arginine such as soy, nuts, seeds, and legumes: “Regulation of brown adipose tissue development and white fat reduction by L-arginine.” (2012).
In an effort to provide some practical take-aways from all of this ongoing research, the author searched “brown fat, beverages” and did find a surfeit of periodicals and blog posts boasting incredible belly-slimming results from drinks such as “Golden Milk Lattes” and “Detox Mint Tea”. While the literature doesn’t quite support this level of success, it certainly can’t hurt, unless you have any allergies or sensitivities to any of the aforementioned ingredients.
All in all, the question still remains, “What can brown do for you?”