Years ago, I participated in a panel at a health and wellness fair sponsored by the Los Angeles Times. On this panel were a number of practitioners, many of them forward-thinking specialists in integrative and functional medicine.

I don’t remember who I shared that panel with that day—I’ve been on more than 100 such panels—but I do remember one pearl of wisdom offered by one of the docs sitting next to me.

When I have a patient with lots of complaints and symptoms I often tell them to do one thing”, he said. “Take your weight, divide by two, and drink that number of ounces of water every day. When they come back to see me in two weeks, 90% of the time their symptoms have significantly improved.

Though there is no real science behind the “8 glasses of water a day” rule, that doesn’t mean it’s not a good idea. About sixty percent of our bodies are water. And if we don’t stay hydrated, the first thing to go is physical and mental performance.

Even as little as a 2% loss of your body’s water content can make a significant difference. (Athletes can lose up to 10% of their water just by sweating.) And let’s not forget that muscle is a whopping 80% water!

Water can also affect mood. One study of young women showed that fluid loss of as little as 1.36% following exercise impaired both their concentration and their mood. It also increased their number of headaches. And in case you think that’s just a “woman” thing, the same thing happens in men. A study in young men found that a fluid loss of only 1.59% increased feelings of fatigue and anxiety. That small amount of dehydration also had an effect (not a good one) on their working memory.

Drinking more water can also help with headaches, kidney stones, and constipation (especially constipation!).

And then there’s weight loss.

In two separate studies, drinking about 17 ounces of water was shown to increase metabolic rate by up to 30% for up to 1.5 hours. A third study showed that dieters drinking half a liter of water before meals lost 44% more weight.

In the weight loss community, it’s long been an article of faith that drinking more water can help you lose fat. The prescription has always been the one my unnamed colleague at that LA Times health fare repeated so many years ago: Take your body weight, divide by 2, and drink that number of ounces of water.

It’s an easy way to make a quick upgrade to your overall health—and it might even help you shed some body fat at the same time!