"Water weight" sounds like it could mean anything, like, the amount a person weighs sopping wet, a person's relationship to gravity in water, or a paperweight made out of water. But this amorphous concept has been part of diet culture since the forever, and it's often used to describe the weight someone loses when they first begin a diet. So, what the heck is water weight?
From a scientific standpoint, "water weight" refers to the amount of water retained in someone's body, explains Evan Forman, PhD, director of the Center for Weight, Eating and Lifestyle Science (WELL Center) at Drexel University. We know that the human body is made up of mostly water, along with bones, muscles, fat, and other tissues, he says. But the amount of water that an individual retains at any given moment depends on various factors, including their sodium and carbohydrate intake, and exercise habits, he says.
When people talk about "water weight," they're usually referring to this shifting amount of water that takes up space and contributes to weight in the human body. "It is 'real' in the sense that the number on the scale partly reflects water weight, and also that when weight is lost or gained, some portion of that change is water," Dr. Forman says. Even though water weight is technically "a thing," that doesn't mean it's something you necessarily need to pay attention to, because this idea of water weight doesn't take into consideration the fact that we're made of water.
Most often, people talk about water weight in the context of weight loss and dieting. In the absence of food or fuel, the body will turn to stores of glycogen, which tend to pull water into cells. (For every gram of glycogen stored in muscles and fat, there's about three grams of water.) That's why when people experience immediate, noticeable weight loss on a diet, they attribute it to "losing water weight." Usually, this water weight is gained back, which people looking to lose weight view as a bad thing, Dr. Forman says. "This can be frustrating, but it helps to explain that some of the initial weight loss was due to the body adjusting to the amount of water it retains due to the change in carbohydrate intake," he says.
Despite the negative connotation that water weight carries, it's important to understand that, "in and of itself, the variations of water weight are not of concern," Dr. Forman says. From a health perspective, there's nothing inherently dangerous about your body retaining water from eating certain foods. Using diuretics or "water pills" to try to try to get rid of "water weight," on the other hand, can be dangerous. There are a number of things that influence the amount of water you retain, such as your menstrual cycle, medications, and even cortisol levels. That said, water retention could reflect an underlying issue, he says. "For example, an overly high-salt diet and not drinking enough water, paradoxically, can lead to excess water retention," he says.
Perhaps all the fuss about water weight can serve as a reminder that a number on a scale is not the only thing that matters. What's more important than worrying about these normal weight fluctuations is ensuring that you're following a diet that's sustainable — not one that's going to lead to short-term gain or loss, Dr. Forman says. And another thing that bears repeating: weight is not the only indicator of health.