Researchers at Vanderbilt University Medical Center led by David Robertson, MD, have shown that ordinary water—without any additives—does more than just quench thirst. It has some other unexpected, physiological effects. It increases the activity of the sympathetic—fight or flight—nervous system, which raises alertness, blood pressure and energy expenditure (a technical term for calorie burning).

Sharp eyed readers may have noticed the reference to increasing blood pressure, something none of us want to do (unless we have very low blood pressure to begin with). But not to worry, while the researchers found that water did not significantly raise blood pressure in healthy young subjects, they did find that water increased sympathetic nervous system activity.

And because it raises sympathetic nervous system activity—and consequently calorie burning—it does promote weight loss.

So how much weight loss are we talking about?
Dr. Robertson calculated that it might be as much as five pounds a year if you drank three 16 ounce glasses of water a day and nothing else changed.

“This is not going to be the answer to the weight problem in the United States,” he said, “but it’s interesting that activation of the sympathetic system is enough to do that.”