According to some estimates, the average adult drinks fewer than five cups of water per day; active adults drink more water than their less-active peers but are still drinking far less than the recommended 64 ounces of water per day — and dehydration could impact the number on the scale.
Research published in the Annals of Family Medicine found an association between dehydration and obesity: Those who drank the least water had the highest body mass index.
“Regardless of your weight, drinking plenty of water throughout the day can help keep you hydrated and feeling your best,” says Tammy Chang, MD, MPH, and an assistant professor of family medicine at the University of Michigan. “It’s a healthy habit that is easy and inexpensive.”
If you’re trying to lose weight, here are four research-backed reasons to drink more water:
1. DRINKING WATER CUTS CALORIES
When it comes to weight loss, choosing iced coffee, soda and sports drinks might make it harder to lose weight. The reason: Choosing these beverages over water could add calories (and pounds).
On the flip side, the more water you drink, the fewer calories you consume, according to research published in The Journal of Human Nutrition and Dietetics. The 2016 study found that those who drink one extra 8-ounce glass of water per day consumed 68 fewer calories; those who drank three extra glasses of water consumed 205 fewer calories, leading to 1/2 pound of weight loss per week.
“I have found that sometimes people may think they are hungry when they are really thirsty,” says Chang. “Drinking water or eating fruits and vegetables, which are high in water content, may help curb that craving and help keep you hydrated.”
2. DRINKING WATER REDUCES FATIGUE
Too tired to work out? Chugging a glass of water could help you go from the couch to the treadmill. “Dehydration can make you feel sluggish,” says Joan Salge Blake, EdD, a dietitian, clinical associate professor of nutrition at Boston University and author of “Nutrition & You.”
Increasing water intake from 1.2 liters (about four 8-ounce glasses) to 2.5 liters (eight 8-ounce glasses) for three days helped improve mood and reduce fatigue, according to a study published in PLOS One. The same study found drinking less water was associated with lower moods, headaches and fatigue — and nothing tanks a workout faster than a headache, bad mood and total exhaustion.
3. DRINKING WATER MAY BOOST METABOLISM
Increasing your water intake can also increase your metabolism. Research published in The Journal of Endocrinology and Metabolism found that drinking 16 ounces of water led to a temporary 30% spike in metabolism. Drinking one-and-a-half more liters of water every day could help you burn 200 more calories daily.
A second study cast doubt on the original, but noted a small increase in metabolism associated with drinking cold water (but no increase after drinking water at room temperature). Although research on the effect of water on metabolism is conflicting, Blake believes water is never a bad choice, noting, “Water is an important nutrient. It’s a refreshing beverage with zero calories.”
4. DRINKING WATER FUELS WORKOUTS
There is a reason the American Council on Exercise recommends drinking 17–20 ounces of water 2–3 hours before a workout, 21–30 ounces per one-hour of exercise and 8 ounces within 30 minutes of finishing a workout. “If you’re trying to work out when you’re dehydrated, you won’t be able to achieve peak performance,” Blake says.
Blake advises weighing in before and after a workout: For every pound of weight lost — which is all water loss — she suggests drinking 2 1/2–3 cups of water. The color of your urine is also a key indicator of hydration, according to Chang.
“Typically, your urine will be very light colored if you are well-hydrated,” she says. “If your urine is dark, then you likely need more water.”