Here’s what you need to know.
Last weeks, a new study made waves on the interwebs. The reason: On the surface, the study’s results seemed to show that a hot bath is a worthy alternative to exercising. But an expert told SELF that the study’s population and parameters seriously limit the findings—and we shouldn’t be running to the tub instead of the gym.
In the study, published in the open-access journal Temperature, researchers split participants into two groups and examined how an hour-long 104-degree hot bath and an hour’s worth of indoor cycling affected blood sugar levels and caloric burn. They found that “cycling resulted in more calories being burned compared with a hot bath, but bathing resulted in about as many calories being burned as a half-hour walk (around 140 calories),” study coauthor, Steve Faulkner, a researcher at Loughborough University, wrote on the news site the Conversation. Researchers also observed that when participants ate a meal following each trial, blood sugar was about 10 percent lower for the hot bath group than the exercise group.
Before you cancel spinning class and invest in new bath bombs, hold on—it’s not that simple. “This study will be interpreted by most people as, ‘[taking hot baths] is a good way to get healthy or even lose weight,’ but that’s not what they’re showing,” Chris Hogrefe, M.D., a sports medicine and emergency medicine physician at Northwestern Memorial Hospital, tells SELF. “The connection between taking a hot bath and this making you healthier isn’t there.”
First, Hogrefe points to the extremely small and unrepresentative sample used in the study: Two groups of seven men between the ages of 20 and 42 . “There are so many populations that don’t fall into this group,” he says. “And in a sample size of seven [participants in each experimental group], it’s very easy to just stumble across this stuff that isn’t indicative of a large group.” Basically, it’s hard to say that anything observed in this study could be applied to the general population.
Even if the study size was, say, larger and more representative, the study still only tested participants on a few benefits of exercise: caloric burn and blood sugar control. But those measures are just two slices of the pie when it comes to the many benefits of exercise. Exercise, for instance, also strengthens the heart, respiratory system, and can help improve mental health. The study didn’t measure how a hot bath impacts any of those benefits, making it impossible to say that a hot bath is “as good as” or the “equivalent of” exercise. Sure, a hot bath may have “similar benefits” to exercise—meaning you can burn calories in a hot bath—but that doesn’t mean it’s as good for your body as exercise.
“You burn calories in the heat, just like you would in the tub, just like you would in the sauna,” Hogrefe says. “But just burning calories doesn’t make you healthier.”
The study itself actually outlines a lot of these limitations—but some people on the internet didn’t read the fine print. When you get into the nitty gritty of the study, it’s really a molecular look at how “passive heating” (meaning being heated from the outside rather than generating your own heat with exercise) could potentially help people mimic the effect of exercise to reap similar benefits. “This study tells us that this may be an area of further investigation and research,” Hogrefe says. “And if you wanted to take a hot bath, it’s not going to hurt you—assuming you don’t scald yourself.”
Clearly there’s still more research needed on this topic—so no, we wouldn’t recommend taking a bath instead of exercising.