Fat is widely viewed as an enemy of our health. Obesity increases the odds of developing a host of problems, including heart disease, type 2 diabetes, hypertension and many types of cancer. Troublingly, obesity rates now top 40% in the US. But researchers recently have uncovered some interesting findings about fat—findings that could help reduce the health risks posed by obesity…and perhaps even lower obesity rates themselves. Among the surprises—the quality of one’s fat might matter more than the quantity.
When people picture fat, they imagine white fat, the most common and familiar form of flab. But mammals, including humans, also have a second type of fat known as brown fat—and brown fat functions differently than white fat in some fundamental and significant ways.
White fat stores energy in case it’s needed later. Brown fat converts energy into heat through the process of mitrochondrial uncoupling of certain proteins. Our ancestors likely developed brown fat as a defense against hypothermia, which was a major threat to early humans.
The fact that humans have some brown fat is not news, but until recently, the scientific consensus was that brown fat played a meaningful role only for newborn babies. Recent finding: Brown fat has a meaningful effect on our health throughout our lives. A 2021 study by a team of researchers at The Rockefeller University and Memorial Sloan Kettering Cancer Center examined the PET scans of more than 52,000 patients and confirmed what many smaller studies already had suggested—people who have significant levels of brown fat have much lower rates of many obesity-related health problems, including type 2 diabetes, coronary artery disease, cerebrovascular disease, congestive heart failure and hypertension, versus similar people who lack significant amounts of brown fat. Brown fat’s health benefits appear to be most pronounced among individuals who are overweight or obese. In fact, type 2 diabetes rates among people who are obese but who have brown fat are similar to those of people who are not obese but lack brown fat.
Theories on how brown fat protects against obesity-related health risks…
Brown fat might burn potentially toxic metabolites, such as glucose, free fatty acids and branched-chain amino acids, as fuel.
Brown fat might influence where the body stores white fat, leading to relatively more “subcutaneous” fat, located under the skin…and less “visceral” fat, also called belly fat, located around the interior organs. Visceral fat is more associated with obesity-related health problems.
Brown fat might secrete beneficial hormones that affect insulin sensitivity and appetite regulation.
Brown fat might provide some protection against obesity itself, not just obesity-related health problems. Mouse studies have found strong associations between increased brown-fat activity and reductions in obesity. It’s not yet clear if humans have sufficient brown fat to experience these weight-loss benefits, but this does create a compelling possibility—that this type of fat might one day help keep us thin.
Mammals have two types of brown fat—the brown fat they’re born with…and inducible brown fat, also called “beige fat.” The inducible brown-fat cells activate their thermogenic properties in response to stimuli that may include cold temperatures, certain drugs and exercise.
Does this mean that people can reduce their risk for obesity-related health issues by intentionally increasing their exposure to these brown-fat–activating stimuli? There isn’t yet sufficient evidence to recommend that—larger and longer-term studies are needed—but some early results are promising…
Cold. Numerous small studies have found that brown fat can be activated by exposure to cold temperatures. In one study by researchers at Maastricht University, 23 of 24 participants showed evidence of brown-fat activity when exposed to cold temperatures. When several of the participants were retested at neutral temperatures, none showed any detectible brown fat activity. Notably, exposure to extreme cold does not appear to be necessary to activate brown fat—these participants were subjected to a cool-but-far-from-frigid 61°F (16°C) for two hours. Another small study by Maastricht University researchers found that exposure to cool temperatures appears to significantly increase insulin sensitivity among people with type 2 diabetes, so perhaps turning down the furnace to activate brown fat could become a diabetes treatment in the not-too-distant future.
Pharmaceuticals. Drugs could one day activate brown fat without the mild discomfort of cool temperatures. In fact, one drug does this already—in a small study, the medication mirabegron, approved in the US for bladder control, has been shown by researchers at the National Institutes of Health to both activate brown fat and increase insulin sensitivity. But there are risks: Mirabegron could elevate heart rate and blood pressure. Based on this finding, though, other drugs that can activate brown fat without this risk could be developed.
Exercise. Studies conducted on mice have found that aerobic activity such as running on a treadmill can activate brown fat. But a recent study involving human subjects was less encouraging—researchers at Spain’s University of Granada found no evidence that 24 weeks of exercise training increased brown-fat activity in previously sedentary adults. But further research is needed before this possibility is discarded.
Genetics. There likely is a genetic component to the varying levels of brown-fat activity observed in different people and population groups. One study by Leiden University Medical Centre researchers found that South Asians living in the Netherlands tend to have less brown-fat activity than Caucasians who live there, for example. That might help explain why South Asians, in general, have significantly higher incidence of type 2 diabetes than Caucasians. Finding that a genetic component does exist could open the door to future gene therapy.
How much brown fat activity do you currently have? There’s no easy way to know—currently this can be determined only by examining PET scans. But studies have uncovered certain trends—brown-fat activity tends to be more prevalent in women than men…in younger people than older ones…and in people with lower body mass indexes than higher ones.
Our brain and our fat use sensory neurons to communicate with each other, according to neuro-scientists at Scripps Research in San Diego. Sensory neurons typically alert the brain to external stimuli—sensory neurons in your skin warn your brain when you touch a hot stovetop, for example.
But it is a surprise to find that these neurons are communicating with both our brown and white fat. Additional research is needed, but this finding has potentially major implications for the treatment of obesity—if the brain is communicating directly with fat, that opens the door to the possibility that science could intercept or modify those messages in ways that encourage the body to store less fat.
