What is brown fat? Study suggests people who have it are less likely to suffer from many health conditions
Researchers have provided evidence suggesting that brown fat may protect against numerous chronic diseases in a new analysis. They found that people with brown fat in their bodies are less likely to suffer from multiple health conditions. Among over 52,000 participants, those who had detectable brown fat were less likely than their peers to suffer cardiac and metabolic conditions ranging from type 2 diabetes to coronary artery disease, the most common type of heart disease that is the leading cause of death in the US.
“For the first time, it reveals a link to lower risk of certain conditions. These findings make us more confident about the potential of targeting brown fat for therapeutic benefit,” suggests Paul Cohen, senior attending physician at The Rockefeller University Hospital. The findings have been published in Nature Medicine.
What do we know about brown fat?
Unlike white fat, which stores calories, brown fat burns energy, and scientists hope it may hold the key to new obesity treatments. According to the National Institutes of Health (NIH), brown fat breaks down blood sugar (glucose) and fat molecules to create heat and help maintain body temperature.
“Brown fat contains many more mitochondria than does white fat. These mitochondria are the ‘engines’ in brown fat that burn calories to produce heat. Brown fat has generated interest among researchers because it appears to be able to use regular body fat as fuel. In addition, exercise may stimulate hormones that activate brown fat. It’s too soon to know whether brown fat's calorie-burning properties can be harnessed for weight loss,” describes a Mayo Clinic blog.
Brown fat has been studied for decades in newborns and animals, but it was only in 2009 that scientists appreciated it can also be found in some adults, typically around the neck and shoulders. From then on, experts have scrambled to study the elusive fat cells, which possess the power to burn calories to produce heat in cold conditions. However, it has long been unclear whether people with ample brown fat truly enjoy better health. For one thing, it has been hard to even identify such individuals since brown fat is hidden deep inside the body.
Large-scale studies of brown fat have been practically impossible because this tissue shows up only on PET scans, a special type of medical imaging. “These scans are expensive, but more importantly, they use radiation. We don’t want to subject many healthy people to that,” explains Tobias Becher, the study’s first author and formerly a clinical scholar in Cohen’s lab.
Becher came up with an alternative. Across the street from his lab, many visit Memorial Sloan Kettering Cancer Center each year to undergo PET scans for cancer evaluation. Becher knew that when radiologists detect brown fat on these scans, they routinely make note of it to make sure it is not mistaken for a tumor. “We realized this could be a valuable resource to get us started with looking at brown fat at a population scale,” Becher adds.
What did they find?
In collaboration with Memorial Sloan Kettering, the researchers reviewed over 130,000 PET scans from 52,487 patients and found the presence of brown fat in nearly 10% of individuals. The authors note that this figure is likely an underestimate because the patients had been instructed to avoid cold exposure, exercise, and caffeine, all of which are thought to increase brown fat activity.
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Several common and chronic diseases were less prevalent among people with detectable brown fat. For example, only 4.6% had type 2 diabetes, compared with 9.5% of people who did not have detectable brown fat. Similarly, 18.9% had abnormal cholesterol, compared to 22.2% in those without brown fat.
The analysis also revealed three more conditions for which people with brown fat have lower risk: hypertension, congestive heart failure, and coronary artery disease, links that had not been observed in previous studies. Another finding was that brown fat may mitigate the negative health effects of obesity. In general, obese people have an increased risk of heart and metabolic conditions. But the team found that among obese people who have brown fat, the prevalence of these conditions was similar to that of non-obese people.
“We report that individuals with brown adipose tissue (BAT) had lower prevalences of cardiometabolic diseases, and the presence of BAT was independently correlated with lower odds of type 2 diabetes, dyslipidemia, coronary artery disease, cerebrovascular disease, congestive heart failure and hypertension. These findings were supported by improved blood glucose, triglyceride and high-density lipoprotein values,” the findings state.
The actual mechanisms by which brown fat may contribute to better health are, however, still unclear, but there are some clues. For example, brown-fat cells consume glucose to burn calories, and it is possible that this lowers blood glucose levels, a major risk factor for developing diabetes, suggest authors.
The team plans to further study the biology of brown fat, including by looking for genetic variants that may explain why some people have more of it than others. These are “potential first steps toward developing pharmacological ways to stimulate brown fat activity to treat obesity and related conditions,” the experts indicate. “The natural question that everybody has is, 'What can I do to get more brown fat? We don’t have a good answer to that yet, but it will be an exciting space for scientists to explore in the upcoming years,” says Cohen.