什么饮料最解渴？白水、茶还是汽水？都不是！苏格兰科学家的研究发现，最补水的饮料含有乳糖、蛋白质和脂肪，你猜出来是哪种饮料了吗？Photo by Boxed Water Is Better on Unsplash
When you're thirsty and in need of a drink, which beverages are best at keeping you hydrated?
Sure, you can always reach for a glass of water -- but plain H20 isn't the most hydrating beverage around, according to a study from Scotland's St. Andrews University that compared the hydration responses of several different drinks.
The researchers found that while water -- both still and sparkling --does a pretty good job of quickly hydrating the body, beverages with a little bit of sugar, fat or protein do an even better job of keeping us hydrated for longer.
The reason has to do with how our bodies respond to beverages, according to Ronald Maughan, a professor at St. Andrews' School of Medicine and the study's author. One factor is the volume of a given drink: The more you drink, the faster the drink empties from your stomach and gets absorbed into the bloodstream, where it can dilute the body's fluids and hydrate you.
The other factor affecting how well a beverage hydrates relates to a drink's nutrient composition. For example, milk was found to be even more hydrating than plain water because it contains the sugar lactose, some protein and some fat, all of which help to slow the emptying of fluid from the stomach and keep hydration happening over a longer period of time.
另一个影响饮料补水功效的因素和饮料的营养成分有关。例如，研究人员发现，牛奶的补水功效甚至比白水更佳，因为牛奶含有乳糖、蛋白质和脂肪，这些成分都有助于减缓液体从胃里排空的速度，延长补水的功效。Photo by Eiliv-Sonas Aceron on Unsplash
Milk also has sodium, which acts like a sponge and holds onto water in the body and results in less urine produced.
The same can be said for oral rehydration solutions that are used to treat diarrhea. Those contain small amounts of sugar, as well as sodium and potassium, which can also help promote water retention in the body.
用来治疗腹泻的口服补水溶液也可以有同样的补水功效。那些含有少量糖、钠和钾的饮料也可以帮助人体留住水分。Photo by Piotr Chrobot on Unsplash
But here's where it gets tricky: Beverages with more concentrated sugars, such as fruit juices or colas, are not necessarily as hydrating as their lower-sugar cousins. They may spend a little more time in the stomach and empty more slowly compared to plain water, but once these beverages enter the small intestine their high concentration of sugars gets diluted during a physiological process called osmosis. This process in effect "pulls" water from the body into the small intestine to dilute the sugars these beverages contain. And technically, anything inside the intestine is outside your body.
Juice and soda are not only less hydrating, but offer extra sugars and calories that won't fill us up as much as solid foods. If the choice is between soda and water for hydration, go with water every time. After all, our kidneys and liver depend on water to get rid of toxins in our bodies, and water also plays a key role in maintaining skin's elasticity and suppleness. It's the cheapest moisturizer you'll find.
While staying hydrated is important -- doing so keeps our joints lubricated, helps prevent infections, and carries nutrients to our cells -- in most situations people don't need to worry too much about how hydrating their beverages are.
"If you're thirsty, your body will tell you to drink more," Maughan said. But for athletes training seriously in warm conditions with high sweat losses, or for someone whose cognitive function may be negatively impacted by working long hours without beverage breaks, hydration becomes a critical issue.
莫恩说：“如果你渴了，身体会告诉你多喝一点。”不过，对于在高温条件下辛苦训练并大量排汗的运动员，或者对认知功能可能因长时间工作无暇喝水而受损的人而言，补水就变得很重要。Photo by Emre Gencer on Unsplash
Alcohol acts as a diuretic, which causes you to pass more urine, so when it comes to alcoholic beverages hydration will depend on a beverage's total volume. "Beer would result in less water loss than whiskey, because you are ingesting more fluid with beer," Maughan said. "Strong alcoholic drinks will dehydrate, dilute alcoholic drinks will not."
When it comes to coffee, how well your java hydrates you will depend on the amount of caffeine you consume. A regular coffee with about 80 milligrams of caffeine would be pretty much as hydrating as water, according to Maughan's research.
Consuming more than 300mg of caffeine, or about 2-4 cups of coffee, could cause you to lose excess fluid as the caffeine causes a mild, short-term diuretic effect. This is more likely to happen with someone who doesn't typically consume caffeine, and it could be offset by adding a tablespoon or two of milk to your cup of joe.
The research team at St. Andrews University tested 13 common beverages to see how they impact hydration. Here's what they found, ranked from most hydrating over a four-hour period to least.
Skim milk 脱脂牛奶
Oral rehydration solutions 口服补水溶液
Full fat milk 全脂牛奶
Orange juice 果汁
Diet Cola 健怡可乐
Cold tea 凉茶
Sports drink 运动饮料
Still water 白水
Sparkling water 苏打水