Research shows cold water could help you burn fat and lose weight

Calorie-burning fat burns energy when we are cold. Now scientists are trying to harness its powers to fight obesity and type 2 diabetes.

When the nights draw in, the leaves fall off the trees, and the outside world becomes blanketed in frost, many of us will be tempted to reach for the thermostat and crank up the heating.

When venturing outdoors, we’ll likely wrap up in a scarf and hat, piling on the layers in a desperate attempt to keep warm. Yet being cold and uncomfortable could be the key to improving health and losing weight.

The reason is all down to a special type of fat called calorie-burning fat. Unlike white fat, which clings stubbornly to thighs, waists and hips, calorie-burning fat burns calories, converting them into heat when we are cold.

Some believe that if harnessed properly, it could make us thinner. Intriguingly, all we theoretically need to do to activate it is to hop into a cold shower or eat lots of spicy foods and caffeine.

But before you jump into an icy lake or down that fourth cup of coffee, it is worth exploring whether the hype behind calorie-burning fat is justified.

How is calorie-burning fat different?

When we are born, each of us has plentiful stores of calorie-burning fat which act like an internal heater.

Babies don’t have enough muscle mass to shiver, so they rely on calorie-burning fat to convert sugars and fats into heat.

Calorie-burning fat cells have a disproportionately high number of mitochondria – the energy-producing factories inside cells.

But unlike normal mitochondria, which produce adenosine triphosphate (ATP) – a kind of universal energy currency the body can use – the mitochondria inside calorie-burning fat cells contain a protein called thermogenin, or UCP1, which allows them to convert calories from food directly into heat instead.

“When stimulated, calorie-burning fat has the capacity to produce 300 times more heat per unit mass than any other tissue or organ in the body,” says Michael Symonds, professor of developmental physiology at the University of Nottingham in the UK.

Most of what we know about calorie-burning fat comes from studies on small mammals such as mice and rats.

These rodents have large reserves of it, which helps them stay toasty and warm during the winter months when they go into hibernation.

“For our ancestors, or for small animals like mice, cold temperatures would have been a major threat to survival, so it was advantageous to have a tissue that could convert energy sources into heat,” says Paul Cohen, an associate professor at The Rockefeller University, New York, who studies molecular metabolism.

Decades of research show that, in mice at least, calorie-burning fat sucks up sugars and fats from the bloodstream.

It also appears to protect mice from obesity and metabolic diseases linked with weight, such as diabetes and heart disease.

Calorie-burning fat in adults

Adult humans are adept at finding other ways to keep warm – turning the heating on, snuggling under a thick duvet or pulling on an extra-warm coat.

It was widely assumed that calorie-burning fat all but disappeared by puberty. This changed in 2009 when researchers from Finland and Sweden showed that adult humans not only still have calorie-burning fat, but in temperatures below 16 °C (60.8°F), it activated and started absorbing glucose and fats from the bloodstream.

Not only that, but thinner individuals had more calorie-burning fat, while obese people had less.

Those with more calorie-burning fat also had higher metabolic rates in the cold, suggesting it could be targeted in obesity treatment.

A 2021 study by Cohen’s team found people with calorie-burning fat had lower rates of type 2 diabetes, heart disease, stroke, and high blood pressure.

It’s not clear if calorie-burning fat is responsible for these benefits. Most adults have very little – just 0.02 to 300g, less than 0.5% of total body mass.

“Whereas white fat can expand almost unlimitedly, calorie-burning fat probably measures in hundreds of grams at most,” says Cohen.

However, it could still boost metabolic health by taking up glucose from the blood or regulating insulin sensitivity.

“Activating calorie-burning fat is unlikely to treat obesity directly but may improve complications from poor metabolism,” Cohen adds.

Cold exposure – ice baths, cold-water swimming, or cryotherapy – can stimulate calorie-burning fat. Noradrenaline released during cold exposure activates the fat.

Studies show that even brief exposure to freezing water two to three times a week improves insulin sensitivity and glucose control.

Cooler, non-freezing conditions can also help. One study found that men sleeping in a room at 19 °C (66°F) for a month increased calorie-burning fat by 42% and improved insulin resistance.

Cold showers, cool room temperatures, and wearing cold vests are other ways to activate it.

Caffeine and capsaicin from chilli can stimulate calorie-burning fat, too, though in impractical doses for a noticeable effect. Ultimately, experts emphasise that activating this fat works best alongside healthy eating, regular exercise, and maintaining good overall lifestyle habits.