How much water do we really need?
“Drink at least eight glasses of water a day” is an adage some obsessively follow. A scientist who undertook an exhaustive hunt for evidence backing all this water advice and came up mostly, well, dry. Now the group that sets the nation’s nutrition standards is studying the issue, too, to see if it’s time to declare a daily fluid level needed for good health – and how much leaves you waterlogged.
Until then, “obey your thirst” is good advice, says Dr. Heinz Valtin, professor emeritus at Dartmouth Medical School, whose review of the eight-glass theory appears in this month’s American Journal of Physiology.
“There’s this conception it can only come out of a bottle,” and that’s wrong, notes Paula Trumbo of the Institute of Medicine’s Food and Nutrition Board, which hopes to decide by March whether to issue the first official water-intake recommendation.
In fact, people absorb much water from the food they eat. Fruits and vegetables are 80 to 95 percent water; meats contain a fair amount; even dry bread and cheese are about 35 percent water, says Rolls. That’s in addition to juices, milk and other beverages.
It’s a myth that water blocks dieters’ hunger. Studies show water with food can help you feel full faster, but that just drinking water between meals has little effect, Rolls says.
So how much do we need? Until the Institute of Medicine sets a level, “if people obey their thirst and they are producing urine of a normal yellow color, that’s a safe sign,” Valtin concludes.