Why you don't need 8 glasses of water a day (and yes, coffee counts)
Today’s issue will be myth-busting the “drink 8 glasses of water a day,” recommendation and discussing just how effective industries, led by company interest, are in influencing the public.
Where did the 8 glasses of water a day recommendation come from, again?
What is it about myths and lore in the fitness industry that people tend to adhere to and perpetuate because “it’s just… common sense.”
In other words, when did this seemingly arbitrary number become the standard across both genders of all the various sizes and activity levels?
If I had to guess, I would say it all started from an opportunity.
An opportunity familiar to this industry, in which, a study is presented to the public. The media distorts it. And companies see a way to leverage that fear for profit.
In this case, a study published by the Food and Nutrition Board in 1945, did advise to, “Drink at least 8 glasses of water a day.” Except the media passed over the very next sentence that follows with “Most of this quantity is contained in foods.”
So, while everyone was concerned that we’re all walking around chronically dehydrated — it only made sense that Sports Drink companies would find a way to influence the source.
Decades of Sports Drinks (such as Gatorade) influencing the science of hydration and athletics have not only contributed to the hype but, even worse, most people recognized them as a “better alternative to water,” — even essential.
If you remember, one of the Sports Drink campaigns that came out of that system touted that we need to drink beyond our thirst because if we wait for our body’s natural thirst mechanism to determine our water intake, it will already be too late.
Except, studies show this isn’t true at all — water balance is very well regulated through various quick, sensitive, and accurate physiological mechanisms.
Thirst is invoked at a rise in plasma osmolality of less than 2%, whereas, most experts would define dehydration as starting when an individual has lost 3% or more of body weight — a rise in plasma osmolality of at least 5%.
In other words, you feel thirsty well before you actually become dehydrated.
And as it turns out, experts who have continued to spread the advice to ignore your body’s natural thirst mechanisms were, not surprisingly, sponsored by companies that sold sugary sports drinks (yeah, you guessed it, Gatorade).
And while this in itself isn’t inherently wrong or novel, researchers who have conflicts of interest are not objective enough to be writing guidelines.
All trends start this way, and all trends have a life cycle. They are born, they become popular, and if they’re profitable enough, they’re funded. It’s why “detoxes,” and “cleanses,” get millions and millions of revenue each year, and why some things, despite the lack of research, just become “common sense.”
To be completely fair, I know the advice to drink “8 glasses of water a day,” is really only intended as a helpful guideline.
However, it has created a lot of confusion, nonetheless.
People want to know if they’re living in a constant state of dehydration and how they’ve somehow managed to survive this far.
Some people just want to know why. They’ve always been told to stay hydrated, but what are they gaining from peeing every 10 minutes?
To start, there are many non-athletic scientifically proven benefits of hydration:
Prevention of UTI and kidney stones
Decreased risk of colorectal cancer and premalignant adenomatous polyps
Water decreases the risk of fatal coronary heart disease
High fluid intake decreased the incidence of urinary bladder cancer in men (Benefit not necessarily true in women)
Benefits are claimed for fatigue, arthritis, asthma, and depression (but more scientific research is needed in these areas).
Improvements to skincare
And on the flip side, there are real risks associated with dehydration.
If you’re mildly dehydrated, you may experience these symptoms:
reduced brain function
extreme fatigue
dizziness or lightheadedness
headaches
dry mouth
dull, itchy skin
If you’re severely dehydrated, you may also experience:
overheating (as a result of unregulated body temperature)
low blood pressure
lack of sweating
That said, we’re really not as dehydrated as people think.
Studies show that not all of the advised liquid needs to be in the form of water.
Coffee, tea, milk, soft drinks, fruits, vegetables, etc are all good sources of water, as well. Rejoice!
While caffeinated drinks may have a mild diuretic effect — meaning that they may cause the need to urinate — they don’t appear to cause fluid loss in excess of the volume ingested.
In 2002, Grandjean et al. examined the effect of caffeinated, non-caffeinated, caloric, and noncaloric drinks on hydration in 18 healthy adult males. At the end of the study, there were no significant effects in body weight changes or standard urinary and plasma variables such as osmolality and concentrations of electrolyte and creatinine.
The authors concluded that “advising people to disregard caffeinated drinks as part of the daily fluid intake is not supported by the results of their study,” and that caffeinated drinks should count toward the daily fluid intake in the vast majority.
Since for the vast majority of adults caffeinated and alcoholic beverages constitute nearly one-half or slightly more of the daily fluid intake, lifting these two restrictions raises the “effective” mean in Americans from the seemingly trivial amount of ∼900 ml to the respectable one of 1,700 ml. And that last figure, of course, doesn’t even include the percentage of water we derive from food and metabolism. Some conclude that even 1,700 ml may be as much as 1 liter in excess of what sedentary adults need to maintain physiological homeostasis.
However, in view of the persistent warning that caffeinated drinks do not count, the advocates of 8 × 8 still continue to tell us that “the average American still doesn’t drink enough water.”
And although this doesn’t seem to fall in line with the average person, this may be true to varying degrees depending on the athlete or their activity level.
Athletes do require a different level of hydration recommendations.
For example, a very recent study suggested that even mild dehydration may increase subjective pain and fatigue during exercise.
Since the rate of sweating and the total amount of sweat lost varies so wildly depending on the environment, intensity, duration, and the type of clothing and equipment worn, mild hypohydration can be extremely common among athletes. And drinking to reduce thirst is often an insufficient strategy for replacing sweat losses.
Failure to replace the salt lost in sweat, combined with the excessive consumption of water or drinks containing no salt increases the risk of hyponatremia.
In hyponatremia, the blood becomes more diluted. To correct this imbalance, osmosis draws water out of the blood and excess water enters all cells and tissues in the body. In extreme cases, pressure builds up inside the skull causing a reduced flow of blood to the brain leading to disorientation, fainting, a coma, and even death.
To add to all of this, Stronger by Science did a great write-up on a very recent study suggesting that even mild dehydration may increase subjective pain and fatigue during exercise. You can read their article here.
In this case, although Sports Drinks are redundant for the casual exerciser, they may be beneficial for athletes in the context of high-intensity exercise at a duration of over an hour or exercising in intense humid/hot conditions with excessive sweating. They have electrolytes such as sodium and potassium — minerals that are vital in nerve cell function and muscle cell function.
If a person exercises at a high level for more than an hour, or in intense heat conditions, Sports Drinks can help maintain electrolyte balance and replace depleted stores of carbohydrates being burned for energy.
Exercise results in the loss of carbohydrates stored as glycogen in muscles and the liver. After an hour of hard exercise, the loss contributes to the feeling of fatigue, either because the brain is affected by a fall in blood glucose concentration due to an inability of the liver to maintain the concentration in the face of demand for glucose by muscle or because the depletion of glycogen stored in muscle reduces the ability of the muscle to do the work. Athletic performance therefore declines.
Drinks containing the appropriate concentrations of salt and carbohydrates consumed at an appropriate rate can offset the losses when consumed before and during exercise and can therefore enhance performance.
For the average individual, water alone is perfectly capable of preventing dehydration and a loss of electrolytes for moderate exercise — and a lot easier on the calories. Athletes who exercise for relatively short periods of time (less than two hours or so) rarely suffer from hyponatremia.
Another common benefit of drinking water is the levels of promoting satiety and the sensation of fullness (though, it’s unknown to what extent this effect reduces food intake, how long the effect lasts, and how much fluid might be needed to influence satiety). It keeps us from consuming unnecessary calories.
Dehydration and sleep deprivation can both manifest as hunger. By drinking water, we provide tools for the body to do all the biological things it’s already doing more efficiently and potentially remove the urge to eat unnecessarily.
Interestingly, there is research that water incorporated into food, as in chicken soup, appears to be more effective as a “preload” in curtailing appetite during a subsequent meal than if the same amount of water was drunk during the preload alongside the same food.
In conclusion, the optimal composition of a drink for training will depend on various factors, including whether it is consumed before, during, or after training, what kind of training session is undertaken, and in what training phase the session occurs.
On occasions, the best drink may contain protein, amino acids, carbohydrates, or only water. Sometimes no drink might be the best strategy.
However, excess water consumption won’t do anything extra besides making you pee more.
The Application:
Prioritize fluid intake throughout the entire day.
Monitoring thirst perception (but not relying on this, exclusively).
Urine output and urine color.
Getting adequate amounts of fluid pre-exercise.
Replacing fluid lost during and immediately after a workout to maintain healthy levels.
The gist: Ensure you’re getting proper amounts depending on your activity levels. Not excessive amounts or following an arbitrary number of “8 glasses per day.”