Health & Wellness

Being well hydrated is associated with healthier body weight, new study finds

When it comes to water and weight, the recommendations can be confusing. Should people drink water before meals to eat less? Should it be cold? Does drinking more water keep the pounds off?

A new study finds a relationship between dehydration and being overweight or obese — but that doesn’t mean chugging water leads to healthier weight.

“We found that U.S. adults who are inadequately hydrated had higher BMIs than people who are adequately hydrated,” Dr. Tammy Chang, an assistant professor of family medicine at the University of Michigan and an author of the study, told TODAY.

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Being properly hydrated is associated with healthier weight, a new study finds.

Related: Does drinking more water keep the weight off? Experts weigh in

What color is your urine?

To see if a relationship between hydration and weight existed, the Michigan researchers examined data from 9,528 participants, ages 18 to 64, from the National Health and Nutrition Examination Survey (NHANES), a nationally representative study of nutritional habits. The researchers looked at urine osmolality, which shows how concentrated the urine is — basically whether someone is hydrated or not. Then the researchers compared that to body-mass index, the measure of a person's body fat based on height and weight. People who were dehydrated had higher BMIs.

“This shows a relationship between inadequate hydration and increasing BMI,” said Wendy Hahn, a nutritionist at University of Wisconsin Health who was not involved in the study. “While we can’t draw a causal relationship, there is definitely something going on there.”

Because they didn't find a cause-and-effect connection between hydration and BMI, the researchers do not understand if being properly hydrated helps people keep their weight down — or if people with lower BMIs have an easier time being hydrated, for example.

“This does not prove one way or another that water or hydration causes a difference in weight,” said Chang.

But, the findings do indicate that hydration is associated with better health.

“Inadequate hydration is not good for you,” Chang said. “People who are dehydrated can feel fatigued, they can have decreased concentration.”

Related: Are you dehydrated? 9 symptoms to look out for

The results indicate that focusing on hydration can be an easy way for people to contribute to overall health.

“It’s more than just what you eat and how you exercise,” Chang said.

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If you think you need 8 glasses of water a day, you're all wet

Play Video - 1:05

If you think you need 8 glasses of water a day, you're all wet

Play Video - 1:05

It's more evidence supporting increased water consumption for health. A recent study also looking at NHANES data found that people who drank three extra cups of water a day ate 205 fewer calories, contributing to a loss of a half a pound a week.

“Water can slightly increase metabolic rate, but by a very small percentage,” said Hahn. “Don’t count on water alone to facilitate the weight loss but it can work in concert with other factors.”

The Institute of Medicine recommends 10 to 12, eight ounce glasses of water a day. But consumption depends on the person and how active he or she is. That’s why Chang tells her patients to look at their urine.

“What color is your urine? If your urine is really dark, you need to drink more water … if it is light, almost like the water you drink, you are drinking enough.”

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