Why water isn’t the best liquid when you’re dehydrated

Every photo you see of people exercising or playing has water bottles in it. The health benefits attached to drinking water range from weight loss to hydration.

According to a new study by researchers at Scotland’s St. Andrews University, however, those water bottles should be milk bottles.

The scientists’ study suggests water isn’t the best beverage for a body in need of hydration. The team studied the effects of 13 common beverages when consumed in the euhydrated state (neither dehydrated or hyperhydrated).

Researchers recruited 72 healthy, physically active men ages 18-35 and divided them into three groups. During the study, each participant drank still water (Highland Spring) and three of the following beverages that were randomly picked for them: cola (Coca-Cola), diet cola (Diet Coke), sports drink (Powerade), oral rehydration solution (Dioralyte), orange juice (Tesco Everyday Value), Lager beer (Carling), hot black coffee (Nescafe Original), hot black tea (PG tips), cold black tea (PG tips), full fat milk (3.6% fa) or skim milk (0.1% fat).

By tracking the men’s urine output after each beverage, the scientists could assign a beverage hydration index, or BHI, to each drink.

The St. Andrews team found that beverages with a little sugar, fat or protein did a better job than water of keeping the men hydrated.

Skim milk — which has a little fat, some protein, the sugar lactose and some sodium— did the best job of hydrating the participants. The sodium in milk “acts like a sponge and holds onto water in the body and results in less urine produced,” CNN wrote.

Fruit juices and colas had higher hydration in first four hours, however, don’t hydrate as well-long term because of their high concentrations of sugar, the researchers found. When that sugar enters the small intestine, water is pulled from the body to dilute it. That results in dehydration.

The researchers ranked the 13 beverages they tested, from most hydrating to least over a four hour period:
Skim milk
Oral rehydration solutions (like Pedialyte or Liquid I.V.)
Full fat milk
Orange juice
Cola
Diet Cola
Cold tea
Tea
Sports drink
Still water
Sparkling water
Lager
Coffee