Does the new ice bath really help you lose weight? Here’s what the science says

As spring approaches, you may be looking forward to a little warmer weather. Not so fast! The latest internet health craze is cold diving. The idea is that immersing your body in ice water can help you build resilience, improve your health, and lose weight. But besides chattering teeth and intense chills, is there more to it?

Much of the inspiration comes from Scandinavia with its “winter sailing culture”. If you’re trying to calculate the benefits, you can’t easily compare the health of those who swim in the winter with those who don’t: those who are strong enough to jump into icy lakes may have been healthier to begin with, meaning their health could be the reason for their winter bathing, and not vice versa.

A 2021 study was detailed: Comparing seven Danish men who regularly winter swimmed to eight who didn’t winter swim, they found that experienced swimmers burned more calories in cold conditions. Perhaps the cold snap “hacked” their metabolism, making it easier to lose weight.

But this was not a big experiment – and not only because it included a small number of people and only one sex. There were already differences in body fat between the two groups, so swimming might not be the only reason their bodies reacted differently.

Laboratory studies have looked at how different tissue samples respond to cold: researchers have found that there are different types of fat cells, and some of them respond to cold temperatures by burning glucose faster.

This is all very interesting and promising, but as one review study puts it, “until we have more concrete scientific evidence, this question will remain moot.”

Have we just received some of this evidence? Last week, neuroscientist and influential online medic Andrew Huberman tweeted the results of a Czech study in which researchers exposed a group of soldiers to cold sprays and cold showers. , quote Hubermanproduced “significant reductions in abdominal fat and waist circumference” and “several psychological improvements”.

Impressive. Or at least that’s how it sounds to you. read studying. Only 49 soldiers participated in it – a sample larger than the 15 people in the Danish experiment, but hardly a huge one. Even more disturbing was the sheer volume of results they contained. In addition to abdominal fat and waist circumference, they measured BMI, total weight, skeletal muscle mass, and lean body mass, as well as nine separate questions about self-reported mental health, life satisfaction, and anxiety. They tested whether any of these measures changed over eight weeks in the experimental group (who applied cold sprays) and in the control group (which did not change). And for some indicators, they divided the sample into males and females and tested them separately.

This meant that they ran over 50 statistical tests, turning the study into a kind of fishing expedition. The more tests you run, the more likely you are to find a false positive: a result that appears over time as if there is a real difference, but is really just due to normal statistical deviation.

Here, in the dozens of tests they ran, the researchers found only four possible outcomes, about as many as we would expect, based on a random set of circumstances. But in summing up their research, they focused very heavily on those few positive results, ignoring a long list of measures that made no difference.

Not only that, they made another statistical error: they looked at whether each measurement in the experimental and control groups had changed separately, but they never checked whether the change in the experimental group was actually greater. This is a problem that has plagued many studies over the years—to the point where entire papers have been written about it—and this one is no exception. In fact, the way they administered the tests meant that it made no sense for them to include a control group at all.

So if this happened to you enjoy Swim in the ice water or take a cold shower, keep going. But given the poor quality of the research we have so far, the rest of us may want to wait until there is good evidence for the health benefits of cold sprays before joining you.