The body fat that can help you lose weight

Want to lose weight or overcome a chronic health problem like type 2 diabetes or heart disease? The answer is simple, but painful: go swim in a cold lake or run out into the snow just wearing a bathing suit. Crazy? Perhaps, but sudden exposure to extreme cold kickstarts a biological process that burns fat and helps the body fight chronic disease.

It’s all to do with a major discovery about the way the body uses energy. It was only in 2009 that researchers discovered our bodies retain a type of fat biologists had believed we shed in early childhood. In fact, the fat—called brown adipose tissue (BAT), or simply brown fat—stays with us throughout our lives, and its main function is to burn calories to maintain a healthy body temperature. 

By comparison, our old friend, white fat, stores calories, and the fat that accumulates around our stomach and thighs as a consequence has long been the target of weight-loss programs around the world.

But it seems we’ve been focusing on the wrong fat. By burning calories, brown fat is a key driver for weight loss, and it does so much more. One of the first major studies into BAT has been carried out by researchers from the Rockefeller University Hospital, who looked at levels of the fat in more than 52,000 people and how it impacted their health. They discovered that those with greater stores of brown fat were less likely to suffer from a range of metabolic conditions including type 2 diabetes and coronary artery disease, still the leading cause of death in the US.1

Just 10 percent of the participants had levels of brown fat that could be detected by positron emission tomography (PET) scans, and this group had half the rate of type 2 diabetes as those with lower BAT stores. They were also less likely to suffer from high blood pressure (hypertension), congestive heart failure and coronary artery disease.

The fat also seems to protect against some of the knock-on effects of being overweight or obese. Usually, overweight people are much more likely to suffer from heart and metabolic problems, but if their BAT stores are high, their risk profile drops to that of someone with a normal, healthy weight. However, most people who are overweight tend to have low BAT levels.

An elusive fat

These are some of the first discoveries about the importance of brown fat, but there’s much more to learn. Why, for instance, do some people have more brown fat than others? Can we produce more of it? And just how does it make us leaner and healthier?

The first problem is in detecting this elusive fat. It collects around the neck and shoulders, but it can be seen only with sophisticated technology such as PET scanning. That was how scientists made their discovery back in 2009, but the cost of the scans makes large-scale research studies almost impossible. 

The Rockefeller researchers ingeniously ‘borrowed’ PET scans of 52,000 patients taken at the Memorial Sloan Kettering Cancer Center across the road from their campus, but without this pre-existing resource, the study would never have happened.

While white fat (white adipose tissue) stores calories, scientists know that brown fat burns them to maintain a healthy body temperature; without their high BAT stores, babies would die of hypothermia after leaving the womb. But the Rockefeller researchers suspect that something even more complex is going on. 

To burn calories, fat cells are consuming glucose in the blood, so-called “blood sugar,” and this process reduces blood glucose levels, which is the major risk factor for type 2 diabetes.

But the fat is also linked to the hormone system, and this connection reduces the risk of hypertension. “We are considering the possibility that brown fat tissue does more than consume glucose and burn calories, and perhaps actually participates in hormonal signaling to other organs,” said Rockefeller researcher Paul Cohen.

It’s not clear why some of us have higher stores of the fat than others, but the Rockefeller researchers suspect a genetic reason. Others think it may be more to do with our exposure to cold weather. Autopsies on people who worked outdoors in the cold discovered high levels of brown fat around the neck and pericardium, the sac that surrounds the heart. 

It’s known that women tend to have twice the amount of brown fat as men, and stores are higher in young people. It’s also inversely related to body mass index; in other words, the fatter you are, the less brown fat you have. On average, our brown fat stores are just 10 percent of our overall fat during mild weather, but this increases during the cold winter months. 

Detectable levels of brown fat are typically seen in 65 percent of adults, and this rises to 95 percent of people when they are exposed to cold temperatures for two hours or so.

Let’s go for beige 

According to one theory, it could be possible to transform white fat cells into brown ones, and thus change their function from storing to burning calories, although quite how this alchemy happens is still open for debate.2

A sudden temperature change could be one way. It turns out that being exposed to the cold sparks a mysterious process where BAT cells develop inside white fat cells. Biologists call this hybrid “inducible brown fat” or beige fat. Beige fat has its own health benefits, especially for bone health and bone mineral density, and this could counter the risk of osteoporosis, particularly after menopause.3

Not surprisingly, people living in polar regions are thought to have higher BAT levels as well as faster metabolisms. The Yakut people of Siberia, for example, have a basal metabolic rate—the average speed at which they burn energy—6.5 percent higher than that found in people of a similar weight who live in warmer climates.4

If you’re averse to the cold, exercise could be another way of turning white cells brown. Exercise produces a peptide hormone called irisin, a discovery that was made only in 2012. Irisin turns white cells into beige or brown ones, which, in turn, improves our energy burning and glucose production.5

There’s early research to suggest that dietary change could also encourage the development of brown cells, and green tea, grape extract, omega-3 fatty acid, curcumin and resveratrol, found in grapes and red wine, could all increase our brown fat stores (see box, right). Mental stress could also turn white cells beige, early research suggests.

No shivering

There’s one simple test that can give you an idea of your own brown fat stores. When we’re cold, we can shiver—but people with higher brown fat stores don’t, or not so readily. 

This phenomenon, which biologists call nonshivering thermogenesis, suggests that the body doesn’t need to get warm by shivering because body temperature is being maintained by brown fat reserves. 

Newborns don’t shiver because of their high brown fat stores, which represent5 percent of their total body weight—and although levels can get depleted with time and weight gain, they never entirely go away.

As we all retain some brown fat, or perhaps somehow white fat cells turn beige, then perhaps there is a way to harness its energy-burning abilities to help us lose weight. It’s estimated that brown fat cells burn an extra 250 calories when they are activated, either through sudden cold or exercise.

In 2016, researchers thought they had found the holy grail of weight loss: they discovered signaling pathways that turned white fat cells into calorie-burning brown or beige ones. Since then, the trail has become tantalizingly cold.

There’s also the concern that by tampering with one process in the body, there’s an unexpected effect somewhere else. The weight loss drug Meridia (sibutramine) was supposed to switch on brown cell activity, but it was withdrawn in 2010 after it was found to increase the rate of heart attack and stroke.

The manufacturer got it half right. In tests on laboratory rats, the drug increased oxygen consumption and body temperature, and the brown fat cells consumed more glucose—18 times more, in fact—which would reverse weight gain and diabetes in one go.

There’s more we don’t know than we do know about brown fat; after all, it was only 13 years ago we discovered we still maintained stores of it into adulthood. But one thing is clear: it’s activated by sudden extreme cold. Skinny dipping in a cold lake, anyone?

Foods for brown fat

There are some foods and minerals that appear to increase brown fat stores; researchers from the Tungi Medical College in Wuhan, China, have prepared a list of some of the likely candidates. 1

• Melatonin

• Berberine

• Green tea

• Menthol

• Resveratrol

• Curcumin

• Capsaicin

• Grape extract