We've all heard the ubiquitous recommendation from experts to drink at least 8-eight ounce glasses of water. The benefits purported to come from this include everything from losing weight, reduction in heart disease, protection from cancer, improvement in skin tone and much more.

But where did this original recommendation come from? And furthermore, is there any hard scientific evidence to support the famous 8x8 claim?

In 2002, Heinz Valtin, a professor of Physiology at Dartmouth Medical School, published an article¹ in which he did an exhasutive review of the current literature regarding the 8x8 claim. He first attempted to locate the original reference from which this recommendation arose. The closest he could come was a book co-authored by renowned nutritionist Dr. Fredrick J. Stare and Dr. Margaret McWilliams in 1974, which stated:

"How much water each day? This is usually well regulated by various physiological mechanisms, but for the average adult, somewhere around 6 to 8 glasses per 24 hours and this can be in the form of coffee, tea, milk, soft drinks, beer, etc. Fruits and vegetables are also good sources of water."

As Valtin points out, the passage was not referenced and appears as a very brief section at the end of the book, making it appear as water was taken up as almost an afterthought. There are no documented scientific studies to back this claim, and there is a huge difference between "...somewhere around 6 to 8 glasses" including food and caffeinated drinks, and the 8x8 glasses of water that is currently recommended.

Another possible source he references would be the 1945 Food and Nutrition Board of the National Research Council which wrote²

"A suitable allowance of water for adults is 2.5 liters daily in most instances. An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."

I highlight the last sentences as it seems that people forget that a large percentage of the food we eat is made up of... you guessed it, WATER. Fruits and vegetables contain 80-90% water by weight. Chicken and beef contain 50-60% water, and even cooked rice and potatoes contain up to 60% water by weight.³ So in the average day at least one liter (or 4 glasses of water) of our water requirements is generally consumed in the form of food each day.

But is it still possible that consuming additional water wil help with weight loss? Once again Valtin could find no specific scientific literature that showed consuming 8x8 improved weight loss. However there did appear to be evidence that showed that consuming foods that had water incorporated in them (chicken soup, protein shakes) were helpful in improving satiety, while just drinking water with a meal had little or no effect⁴

Futhermore, evidence exists that since the 8x8 recommendation, many people have increased their intake of soft drinks and sweetened juices. This may in fact have paradoxically worsend the problems with weight gain we've seen in the past 30 years.

I find Vatin's conclusions identical to my personal clinical experience. Our bodies posess a finely tuned internal regulatory mechanisms that tell us, through our thirst, when we need more fluid intake. While there are certainly situations that require increased water intake (intense exercise, fever, diarrhea, dehydration), the vast majority of the time we can use our thirst as an accurate guide to our daily fluid needs.

However one important issue that you should make yourself aware of is to distinguish the sensation of thirst from that of hunger. At times, you may confuse the two, so it's not a bad idea to drink water or a non-caloric beverage first and see if the sensation disappears, saving yourself from unnecessary calorie intake.