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The #1 Myth About Coffee You Need to Stop Believing, Say Experts

This myth has some truth to it, but it's mostly wrong.

With coffee being one of the most popular drinks in America, it's almost irresponsible for any myths to be circulating about the beverage. So when we heard this coffee "fact" the other day, we figured it was high time to bust this myth—with the help of experts.

You've either read it or heard it before: coffee is dehydrating. While this myth has a kernel of truth—that coffee has a diuretic effect—the evidence shows that coffee's diuretic properties aren't enough to make java dehydrating.

We asked experts to explain how it's possible that coffee can technically have dehydrating properties without causing dehydration.

Coffee may have a diuretic effect, but it's not likely to dehydrate you

"Diuretics are any substances that cause your body to make more urine," explains Leann Poston, MD, MBA, MEd, a content contributor for Invigor Medical, adding that, technically, "any fluid that you drink will cause an increase in urine production to maintain a normal fluid balance in the body."

Caffeinated beverages, like coffee, have a mild diuretic effect, but this does not increase the risk for dehydration, registered dietitian Adriana Chychula, MS, RD, LDN tells us. "This diuretic effect is small and is offset by the fluid content of the drink, so you still end up with net hydration," she says.

"One meta-analysis analyzed the results of 16 studies with a median caffeine dose of 300 milligrams, or the equivalent of about three 8-ounce cups of coffee. There was a small diuretic effect related to moderate caffeine consumption compared to non-caffeine conditions, but it was not enough to put a healthy and otherwise hydrated individual at risk for dehydration," explains Chychula.

"The review also found that the minor diuresis was actually negated by exercise," adds sports dietitian Kelly Jones MS, RD, CSSD. "They concluded that concerns about unwanted fluid loss with caffeine intake (in moderate amounts) are unwarranted, especially when it's ingested pre-exercise."

Jones highlights another PLoS One study, which looked at men who regularly consumed 4 cups of coffee per day to see whether they would be more or less hydrated when drinking coffee or water. "They found no significant differences in total body water. However, these subjects were adapted to regular intake of caffeine," Jones explains.

There are still some negative side effects of drinking coffee

Although it's hard to become dehydrated by drinking coffee, that doesn't mean coffee is free of any negative side effects.

"One to two cups [of coffee] can contribute to your fluid intake, however, larger amounts may begin to have negative effects on the body, particularly when intake results in caffeine consumption greater than 6-9 milligrams per kilogram of body weight," says Jones. (Related: Ugly Side Effects of Drinking Too Much Coffee, According to Science)

She also notes that coffee can affect certain people in more intense ways than others.

"Some individuals may respond to caffeine differently than others. While we have a while to go before our DNA can provide adequate information about personalized diets, two genetic mutations—which occur in roughly 1 in 4 people—have been identified and studied for their impact on caffeine tolerance. While coffee can offer health benefits to most individuals, it's possible there may be a greater diuretic effect in individuals [with the DNA mutations] and may have negative cardiac outcomes in response to regular coffee/caffeine intake," says Jones.

Can coffee count towards your daily fluid intake?

Despite its mild diuretic effect, coffee is still mostly water. And something that's so liquid-based will certainly help you stay hydrated.

"Literature suggests that when consumed in moderation, coffee provides similar hydrating qualities as water," says Hailey Gorski, RD, a registered dietitian nutritionist and founder of The Tipsy Kale.

Does this mean you should rely on coffee as your main source of hydration? Not quite.

"Water is [still] your best bet [for hydration] because it is easily accessible and inexpensive, making it the most practical hydration option," says Gorski. "Aim to drink half your body weight in fluid ounces every day. I encourage my clients to reach their hydration goals by drinking water."

For more ways to drink coffee in a way that will support your health and hydration goals, read up on these 7 Things You Should Never Add to Your Coffee.

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Olivia Tarantino
Olivia Tarantino is a senior editor of Eat This, Not That!, specializing in nutrition, health, and food product coverage. Read more
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