With the recent discussion of water intake and health- here is an excerpt from The Original Prescription that discusses the principle of using water as our main source of hydration and a little bit about the origins of the 8 glasses per day “rule.”
This is just one of over 50 Lifestyle principles discussed in the Original Prescription.
Principle #6: Water should be your primary beverage; drink enough, and try to limit the number of liquid calories you consume.
Water is one of the quintessential nutrients of life and yet is often one of the most commonly neglected. Despite its great importance for nearly every bodily function, many of us are still at a loss when it comes to knowing how much we’re supposed to drink each day and which other beverages count toward our daily needs. All this confusion about water needs comes as no surprise considering that the first official recommendation for adequate intake (AI) of water was only established in 2004 by the Institute of Medicine, coinciding with an increase in popular awareness about water needs for preventing conditions such as cancer, heart disease, and weight gain (27). Prior to that, the RDA concluded that it was impossible to set a recommendation for water needs, and the National Research Council used a general rule of thumb of 1 ml/ kcal (that would be two liters of water per 2000 calories consumed, if you’re getting out your calculator) (28). Today’s recommendations for daily water requirements, however, are based on national averages from the NHANES III data, although individual needs vary greatly. It’s estimated that most of us need to get 80% of our daily hydration through beverages, mostly water, while about 20% of our hydration comes from the food we eat (less if you happen to avoid fresh fruits and vegetables) (28).
Throughout history, humans have relied on water as their primary source of hydration, struggling to ensure both an abundant and a clear source was available for their survival. Unfortunately, this struggle still exists in many locations around the world today. In the West, water abundance (at least for drinking) is rarely in jeopardy, and yet many choose other options. Countless individuals have replaced water with soft drinks to quench their thirst, and, as a result, sweetened beverages have become one of the major sources of calories in the American diet. Consumption of high fructose corn syrup, the major sweetener in commercial soft drinks, increased over 1000% between 1970 and 1990, and today, half of all Americans consume soft drinks every day. In fact, these beverages now constitute the leading source of added sugar in the average diet (29,30). To make matters worse, the calories provided by soft drinks often fail to satisfy hunger the way solid food does, nor do they quench our thirst in the way water can, making sugary beverages a key player in the obesity epidemic (30–33). If you want to maintain those good signals that your body is waiting for, limit the number of calories you consume through drinks. So how much water should you drink per day? Well, that depends. How much you weigh (roughly 60% of that is water), how much water you lost recently to perspiration, and relative humidity will all affect the ultimate answer. The Institute of Medicine says that the adequate intake of total water per day is 3.7 liters for men and 2.7 liters for women.† The “8 by 8 rule” (8 glasses of 8 oz. each) equates to about 2 liters. Many rely on their thirst to tell them when to drink, and while it is true that most people’s thirst and hunger mechanisms can help manage their net water balance, in many people the thirst mechanism is blunted and mild dehydration can set in well before their body tells them to drink. Others try to rely on the color and darkness of their urine as a gauge of hydration, but this is not always a reliable indicator of the need for water (35)
So what’s the bottom line when it comes to hydration and water?
- If you aren’t already doing it, drink mostly water to keep yourself hydrated.
- Make sure your water source is clean and free of contaminants.
- Tea and coffee are fine for most people (in moderation); if the caffeine causes you to urinate frequently, consider offsetting this loss with additional water.
- Alcohol is dehydrating—plain and simple.
- Remember to include water-based soups and stews, herbal teas, and low-sugar fruit juices.
- Drink more water when you are physically active and when the weather turns hotter.
† The AIs provided are for total water in temperate climates. All sources (according to IOM) can contribute to total water needs: beverages (including tea, coffee, juices, sodas, and drinking water) and moisture found in foods. Moisture in food accounts for about 20% of total water intake.