Americans told to avoid coffee during extreme heat warning in 3 states

Americans are being advised to avoid drinking coffee in three states where "extreme" temperatures are being forecast this week.

The National Weather Service in Las Vegas issued an extreme heat warning for Wednesday and Thursday in portions of California, Arizona and Nevada.

A social media post from the National Weather Service included a "do" and "don't" graphic.

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The National Weather Service encourages people to stay hydrated, use sunscreen for protection and plan outdoor activities during cooler parts of the day.

It also cautioned against drinking alcohol and caffeine and eating heavy foods.

A similar warning was also issued for Father's Day.

"When it's really hot outside, it's a good idea to think twice before reaching for that cold beer or cocktail," Lauren Manaker, a registered dietitian-nutritionist in South Carolina, told Fox News Digital. 

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"Alcohol can actually make it harder for your body to stay hydrated."

Alcohol is a diuretic, "which means it makes you lose more fluids than you take in," Manaker said. So it leaves you "more at risk for dehydration."

"Plus, it can interfere with your body's ability to regulate temperature, making you feel even hotter and potentially leading to heat exhaustion or worse," Manaker said. 

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Moderate consumption of caffeinated beverages like coffee or tea "doesn't drastically increase your risk of dehydration," Manaker noted, "and for many people, it can still be part of their daily routine, even in hot weather."

"It's important to consider the quantity when consuming caffeinated beverages," Manaker said. 

"One cup of coffee or tea is unlikely to cause significant dehydration for most individuals, especially when balanced with adequate water intake throughout the day."

But it's still "important to pay attention to how your body reacts," Manaker said.

"Caffeine can act as a mild diuretic when consumed in larger quantities."

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One "surprising hydrating choice" to consider is milk, Manaker said.

"Research has found that milk actually hydrates better than water or sports drinks," she said. 

"This is because milk is packed with natural electrolytes like potassium, sodium, magnesium and calcium, along with carbohydrates and protein, which help your body recover and retain fluids after exercise."

A 2016 study from the University of St. Andrews School of Medicine in Scotland revealed that fat-free milk was the top hydrator, while whole milk was the third-best performing of the drinks tested. 

Coffee was the least hydrating, according to the study.

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The National Weather Service also advised against eating heavy foods that "can be harder for your body to digest, and on a very hot day, this can leave you feeling sluggish and overheated," Manaker said.

"When you eat a large, heavy meal, your body has to work harder to break it down, which can actually raise your internal temperature," she said. "This extra effort might make it even tougher to stay cool in the heat." 

Instead, Manaker said, try lighter meals with fresh ingredients like salads, grilled vegetables or lean proteins.

They're "easier on your system and can help you feel more energized and comfortable."

Watermelon is another "excellent choice," Manaker said.