You put in the work. You put out a ton of sweat. Surely, you’ve lost weight, right? Downer alert: Sweating the only sort of helps you lose weight. Technically, sweating can take your weight down, which explains why sauna suits are popular with people like wrestlers who need to make weight in a hurry. If you sweat out 20 ounces of fluid, you’ll “lose” 20 ounces on the scale.
But you’ll bring those pounds right back on when you down that much water after your workout (which you should do), explains Robert A. Huggins, Ph.D., president of research and athlete performance and safety at the Korey Stringer Institute at the University of Connecticut. “It’s not fat mass, which is the weight most people have the goal of losing,” he says.
Of course, over time, working out consistently can help you lose weight, but you can’t judge how effective your workout is just by how much you sweat.
Wait, more sweat doesn’t mean you got a better workout?
Shedding a lot of sweat isn’t the main indicator that you worked hard. True, the harder you work out, the more you’ll sweat. But the fluid loss doesn’t tell you the whole story.
“Each person has their own sweat rate, and it can change over time,” says Huggins. So the guy next to you on the treadmill sweating buckets isn’t necessarily outpacing you. On top of that, how much you sweat can depend on a number of things:
- The environment you’re in. Sounds kind of obvious, but when people are wringing out towels and planning on extra dessert after an indoor cycling workout, they may not be remembering that the AC wasn’t blasting as much as usual. Or that it was more humid than it was yesterday. “When it’s humid, you’re going to lose the same amount of sweat as in a hot, dry environment, if not more,” Huggins says. “But in a humid environment, the air is more saturated with moisture and your sweat can’t evaporate.” More collects on the towel and the floor, but not because you have been working so much harder. If you want to compare how much you’re working from one day to the next, measure power (ideal) or distance or another metric.
- How well adapted to the heat you are. “Your sweat rate goes up once you become more heat acclimatized; that’s what allows you to cool more efficiently and keep working out,” says Huggins. When you’re used to training in the heat, your body basically turns on its air conditioner faster and cranks it higher than someone who’s not used to working out in the heat (which is why you can out-bike and out-run them when you learn the secrets of heat acclimatization).
How to lose weight by sweating
In order to do a quality workout that actually will burn calories or build muscle, you have to replace the fluid you’re losing. Otherwise, your heart rate will go up and your body will likely slow down during that workout, which isn’t going to help you get the weight loss workout you were going for.
Here’s how it works: “You have a set amount of blood that has to go to multiple places when you’re working out—it needs to go to your brain, your muscles, and your skin for a cooling,” Huggins says. When you sweat, your blood volume decreases if you don’t replace the fluids you’re losing. Your brain, muscles, and skin still need it, but now there’s less to go around. So your heart rate increases, your workout feels harder, and you’ll probably slow down (or pass out if you really don’t pay attention to what it’s telling you).
The ultimate way to keep your workout going during that session, as well as day after day, is to replace what you lost with this simple move, says Huggins.
- Weigh yourself naked before your workout; hold the bottles you’ll drink during the workout.
- Weigh yourself after the workout.
- The before/after difference is how much fluid you lost, meaning how much you’ll want to replace before the next session.