How many glasses of water a day?

A place to get your questions answered from expert dietitian Jeff Novick, RD

Moderators: JeffN, carolve

How many glasses of water a day?

Postby Jackie J » Fri Mar 21, 2008 9:33 pm

Hi Jeff,
I'm sure the good dr. covers this in his books, but just to fact-check, should I be aiming for a certain amount of glasses of water a day on the McDougall plan?
Thank you
Jackie J
 
Posts: 502
Joined: Thu Oct 19, 2006 4:38 pm

Re: How many glasses of water a day?

Postby JeffN » Sat Mar 22, 2008 7:44 am

Jackie J wrote:Hi Jeff,
I'm sure the good dr. covers this in his books, but just to fact-check, should I be aiming for a certain amount of glasses of water a day on the McDougall plan?
Thank you

Hi Jackie

Over the years, there have been many attempts to come out with recommendations and guidelines for the amount of water humans should consume. However, none of them are accurate. There are so many variable that come into play, and are different for each person, that no single guidelines could ever work.

For many years, we heard that thirst was not a good indicator of hydration status, especially in athletes, and we were all told to drink lots of fluids and given all kinds of formulas to follow. it turns out that not only may thirst be an adequate indicator, but some of the formulas resulted in over hydration, which caused its own set of problems. Many athletes who were following the advice of these formulas, developed exercise- associated hyponatremia, a condition in which the body's sodium concentration is diluted too much and several died from this.

In fact, in an article that was published in the Clinical Journal of Sports Medicine, July 2006, the authors concluded "the best approach is to replace fluids is in response to thirst."

They also said that there is no "blanket advice" to give to people about how much fluids are needed. Instead, they said, people should be encouraged "to explore, understand and be flexible toward their own needs."

"Athletes should learn to trust the sensation of thirst, rather than adhere to rigid guidelines that do not allow for the flexibility that is needed in a dynamic situation."

They recommend that people drink when they feel thirsty, as the best way to protect against consuming too much or too little fluids.

I agree.

If you are consuming the typical American diet, which is high in refined, processed foods, the average moisture content of these foods can be as low as 3%. In addition, the typical American diet is very high in salt, which will also increase your thirst. However, if you are eating a diet based on unrefined intact starches, they are around 70% moisture, and you are adding in lots of fresh fruits and veggies, which are about 90% moisture, than you are getting lots of water from one of the best sources possible, your food.

I always tell people to follow healthy dietary guidelines as recommended here, including lots of fresh fruits, vegetables, starchy vegetables, intact whole grains, and legumes and then, let thirst be your guide.

If you are thirsty, drink.

In Health
Jeff Novick, MS, RD
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am

Postby Jackie J » Sat Mar 22, 2008 10:06 am

aaah - thanks for the clarification
Jackie J
 
Posts: 502
Joined: Thu Oct 19, 2006 4:38 pm

Postby Jaggu » Mon Mar 24, 2008 8:55 am

Is there any harm in sipping water in between as you eat? The thought there is to fill up your stomach with somewhat water so you don't eat as much.

I have read that you should drink water an hour prior to you eat and then after you eat but not while eating. I don't know whether this is backed by science or hearsay.
Jaggu
 

Postby JeffN » Mon Mar 24, 2008 9:46 am

Hi Jaggu

Jaggu wrote:Is there any harm in sipping water in between as you eat?


Not that I know of.

Jaggu wrote: The thought there is to fill up your stomach with somewhat water so you don't eat as much.


While the thought is excellent in theory, it doesn't work in application. As I have mentioned, water is the key to lowering calorie density and also increasing bulk and satiety in foods. However, this is only when the water is part of the food and bound up in the food.

So, if you compare eating a bowl of fresh grapes, with eating a bowl of the equivalent amount of raisins (in calories) and drinking the equivalent amount of water (that would have been in the grapes) the water and raisins combo will not be as filling as the grapes.

The reason is, the water consumed with the raisins leaves your stomach in 5 minutes or so. But, the water that is contained within the grapes as part of the whole matrix, can stay in your stomach for an hour or more,

Jaggu wrote:I have read that you should drink water an hour prior to you eat and then after you eat but not while eating. I don't know whether this is backed by science or hearsay.


Both of those statements are hearsay.

You should drink when thirsty.

In Health
Jeff Novick, MS, RD
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am

Water Consumption

Postby margiereilly » Mon Mar 24, 2008 6:43 pm

In addition to the McDougall Ten Day program, I also attended a WEIMAR, CA NEWSTART program. Up at Weimar, they suggest that one consume the liquid such as water about an hour before or two hours after the meal. The theory is that one needs to eat, mix the saliva with the food by chewing very well. Water dilutes the contents of the stomach so that the stomach is not full of the whole foods and craves more food sooner.

I do know that I tend to not chew the food well if I am drinking liquids with my meals. It is important to thoroughly begin the digestion in the mouth prior to getting it into the stomach. So, the WEIMAR approach is to not have liquids with meals. It seems odd but it is not too hard to do it that way.
margiereilly
 
Posts: 203
Joined: Fri Nov 03, 2006 10:17 am
Location: California

Re: Water Consumption

Postby JeffN » Mon Mar 24, 2008 7:23 pm

margiereilly wrote:In addition to the McDougall Ten Day program, I also attended a WEIMAR, CA NEWSTART program. Up at Weimar, they suggest that one consume the liquid such as water about an hour before or two hours after the meal. The theory is that one needs to eat, mix the saliva with the food by chewing very well. Water dilutes the contents of the stomach so that the stomach is not full of the whole foods and craves more food sooner.

I do know that I tend to not chew the food well if I am drinking liquids with my meals. It is important to thoroughly begin the digestion in the mouth prior to getting it into the stomach. So, the WEIMAR approach is to not have liquids with meals. It seems odd but it is not too hard to do it that way.


Thank you.

I agree that we need to chew our food thoroughly as it is an important part of digestion.

I understand the "theory" and where it originally came from (the old natural hygiene philosophy of the early 1800s), and why it has influenced many programs,especially those that have some roots in that philosophy and time, but it not supported by what we know of digestion today. I know of no studies on digestion or on the physiology of digestion that support this theory.

Pitchers of water and teas are available at all the tables during meal time at the McDougall programs.

High water content foods actually increase satiety and keep you full longer that dry foods.

Here is another way to look at it.

Most Americans eat foods that are very dry and concentrated in calories (refined carbs, sugars, flours, grains and highly processed and refined foods). They have a very low moisture content, averaging somewhere around 30-40%, with many refined processed foods as low as 3%.

On the other hand, fresh fruits and vegetables, starchy vegetables, intact whole grains, and legumes are around 70-90% moisture (water content).

A bagel and cream cheese for breakfast is fairly dry compared with a bowl of oatmeal and fresh fruit. A sandwich on bread with a cold cut, with some crackers and cheese is fairly dry compared to a meal of a nice size salad, steamed veggies and a baked potato and a piece of fruit.

Now, according to this theory, the healthy meals would actually be unhealthy for digestion because their high water content would dilute out the digestive enzymes.

After all, what difference would it make to the stomach if the water came from a glass of water that you drank during the meal, or if it came from te high water content that came along as part of the food?

It doesn't.

Eating high water content natural foods is a key to good health and long life.

Avoiding drinking water with meals will not hurt anyone, however, it is not necessary.

In Health
Jeff Novick, MS, RD
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am

That explains why

Postby SactoBob » Mon Mar 24, 2008 8:34 pm

Since I have gone to this style of nutrition from the SAD that my thirst and water consumption have gone down, but my urine output has gone up. I was worrying a bit that I was not drinking the water that most authorities say should be consumed.
SactoBob
 

Re: That explains why

Postby JeffN » Tue Mar 25, 2008 5:46 am

SactoBob wrote:Since I have gone to this style of nutrition from the SAD that my thirst and water consumption have gone down, but my urine output has gone up. I was worrying a bit that I was not drinking the water that most authorities say should be consumed.


Hi Bob,

The reason your thirst & water consumption has "appeared" to have gone down is due to my point above. The food you are now consuming is very high in water content and can be as high as 70-90% water content. The typcial American diet is full of foods that are very low in water content averaging somewhere around 30-40%, with many refined processed foods as low as 3%.

So, since you are getting so much water naturally through the food you are consuming, your thirst has gone down.

The reason your urine output has gone up because these diets have a diuresis effect. In addition, your sodium intake has more than likely gone way down, your total water intake (though through food) has more than likely gone up, you are probably lsoing some weight & are not retaining any fluid you might have been.

Your experience is very common, especially in the beginning days, weeks and sometimes even longer.

It is a good thing. Just always know where there is a near-bye bathroom. ;)


In Health,
Jeff Novick, MS RD
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am

Postby JeffN » Tue Mar 25, 2008 7:01 am

Here is one more study, the abstract and the public press release from the study.

(BTW, in addition, it is interesting to note that the 8 glasses a day is considered an Urban Myth by Snopes.)

http://www.snopes.com/medical/myths/8glasses.asp

Am J Physiol Regul Integr Comp Physiol. 2002 Nov;283(5):R993-1004.

"Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 x 8"?
Valtin H.

Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03756-0001, USA. heinz.valtin@dartmouth.edu

Despite the seemingly ubiquitous admonition to "drink at least eight 8-oz glasses of water a day" (with an accompanying reminder that beverages containing caffeine and alcohol do not count), rigorous proof for this counsel appears to be lacking. This review sought to find the origin of this advice (called "8 x 8" for short) and to examine the scientific evidence, if any, that might support it. The search included not only electronic modes but also a cursory examination of the older literature that is not covered in electronic databases and, most importantly and fruitfully, extensive consultation with several nutritionists who specialize in the field of thirst and drinking fluids. No scientific studies were found in support of 8 x 8. Rather, surveys of food and fluid intake on thousands of adults of both genders, analyses of which have been published in peer-reviewed journals, strongly suggest that such large amounts are not needed because the surveyed persons were presumably healthy and certainly not overtly ill. This conclusion is supported by published studies showing that caffeinated drinks (and, to a lesser extent, mild alcoholic beverages like beer in moderation) may indeed be counted toward the daily total, as well as by the large body of published experiments that attest to the precision and effectiveness of the osmoregulatory system for maintaining water balance. It is to be emphasized that the conclusion is limited to healthy adults in a temperate climate leading a largely sedentary existence, precisely the population and conditions that the "at least" in 8 x 8 refers to. Equally to be emphasized, lest the message of this review be misconstrued, is the fact (based on published evidence) that large intakes of fluid, equal to and greater than 8 x 8, are advisable for the treatment or prevention of some diseases and certainly are called for under special circumstances, such as vigorous work and exercise, especially in hot climates. Since it is difficult or impossible to prove a negative-in this instance, the absence of scientific literature supporting the 8 x 8 recommendation-the author invites communications from readers who are aware of pertinent publications.

PMID: 12376390



'Drink at least 8 glasses of water a day' -- Really?
Dartmouth professor finds no scientific evidence for '8 x 8'

Hanover, NH -- It has become accepted wisdom: "Drink at least eight glasses of water a day!" Not necessarily, says a DMS physician Heinz Valtin, MD. The universal advice that has made guzzling water a national pastime is more urban myth than medical dogma and appears to lack scientific proof, he found.

In an invited review published online by the American Journal of Physiology August 8, Valtin, professor emeritus of physiology at Dartmouth Medical School, reports no supporting evidence to back this popular counsel, commonly known as "8 x 8" (for eight, eight-ounce glasses). The review will also appear in a later issue of the journal.

Valtin, a kidney specialist and author of two widely used textbooks on the kidney and water balance, sought to find the origin of this dictum and to examine the scientific evidence, if any, that might support it. He observes that we see the exhortation everywhere: from health writers, nutritionists, even physicians. Valtin doubts its validity. Indeed, he finds it, "difficult to believe that evolution left us with a chronic water deficit that needs to be compensated by forcing a high fluid intake."

The 8 x 8 rule is slavishly followed. Everywhere, people carry bottles of water, constantly sipping from them; it is acceptable to drink water anywhere, anytime. A pamphlet distributed at one southern California university even counsels its students to "carry a water bottle with you. Drink often while sitting in class..."

How did the obsession start? Is there any scientific evidence that supports the recommendation? Does the habit promote good health? Might it be harmful?

Valtin thinks the notion may have started when the Food and Nutrition Board of the National Research Council recommended approximately "1 milliliter of water for each calorie of food," which would amount to roughly two to two-and-a-half quarts per day (64 to 80 ounces). Although in its next sentence, the Board stated "most of this quantity is contained in prepared foods," that last sentence may have been missed, so that the recommendation was erroneously interpreted as how much water one should drink each day.

He found no scientific studies in support of 8 x 8. Rather, surveys of fluid intake on healthy adults of both genders, published as peer-reviewed documents, strongly suggest that such large amounts are not needed. His conclusion is supported by published studies showing that caffeinated drinks, such as most coffee, tea and soft drinks, may indeed be counted toward the daily total. He also points to the quantity of published experiments that attest to the capability of the human body for maintaining proper water balance.

Valtin emphasizes that his conclusion is limited to healthy adults in a temperate climate leading a largely sedentary existence -- precisely, he points out, the population and conditions that the "at least" in 8 x 8 refers to. At the same time, he stresses that large intakes of fluid, equal to and greater than 8 x 8, are advisable for the treatment or prevention of some diseases, such as kidney stones, as well as under special circumstances, such as strenuous physical activity, long airplane flights or hot weather. But barring those exceptions, he concludes that we are currently drinking enough and possibly even more than enough.

Despite the dearth of compelling evidence, then, What's the harm? "The fact is that, potentially, there is harm even in water," explains Valtin. Even modest increases in fluid intake can result in "water intoxication" if one's kidneys are unable to excrete enough water (urine). Such instances are not unheard of, and they have led to mental confusion and even death in athletes, in teenagers after ingesting the recreational drug Ecstasy, and in ordinary patients.

And he lists other disadvantages of a high water intake: (a) possible exposure to pollutants, especially if sustained over many years; (b) frequent urination, which can be both inconvenient and embarrassing; (c) expense, for those who satisfy the 8 x 8 requirements with bottled water; and (d) feelings of guilt for not achieving 8 x 8.

Other claims discredited by scientific evidence that Valtin discusses include:

* Thirst Is Too Late. It is often stated that by the time people are thirsty, they are already dehydrated. On the contrary, thirst begins when the concentration of blood (an accurate indicator of our state of hydration) has risen by less than two percent, whereas most experts would define dehydration as beginning when that concentration has risen by at least five percent.

* Dark Urine Means Dehydration. At normal urinary volume and color, the concentration of the blood is within the normal range and nowhere near the values that are seen in meaningful dehydration. Therefore, the warning that dark urine reflects dehydration is alarmist and false in most instances.

Is there scientific documentation that we do not need to drink "8 x 8"? There is highly suggestive evidence, says Valtin. First is the voluminous scientific literature on the efficacy of the osmoregulatory system that maintains water balance through the antidiuretic hormone and thirst. Second, published surveys document that the mean daily fluid intake of thousands of presumably healthy humans is less than the roughly two quarts prescribed by 8 x 8. Valtin argues that, in view of this evidence, the burden of proof that everyone needs 8 x 8 should fall on those who persist in advocating the high fluid intake without, apparently, citing any scientific support.

Finally, strong evidence now indicates that not all of the prescribed fluid need be in the form of water. Careful peer-reviewed experiments have shown that caffeinated drinks should indeed count toward the daily fluid intake in the vast majority of persons. To a lesser extent, the same probably can be said for dilute alcoholic beverages, such as beer, if taken in moderation.

"Thus, I have found no scientific proof that absolutely every person must 'drink at least eight glasses of water a day'," says Valtin. While there is some evidence that the risk of certain diseases can be lowered by high water intake, the quantities needed for this beneficial effect may be less than 8 x 8, and the recommendation can be limited to those particularly susceptible to the diseases in question.
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am

Postby JeffN » Sun Sep 07, 2008 10:22 am

Lancet 372, Issue 9641, 782-784 (6 September 2008-12 September 2008)
Comment

The fluid craze
François Lettea, and Jamie P Dwyerb


The notion of "just add water" has been dealt a blow in an editorial in the nephrology press.1 Negoianu and Goldfarb reviewed the literature and found a lack of evidence for or against the recommendation to drink eight glasses of about 0·24 L of liquid daily. A commonly held belief is that we should drink more fluid. In fact, losing a percentage point of plasma volume does not affect perfusion pressures or even the pulse, yet advertisers whisper about 1% or 2% of dehydration. They would educate us on the perils of dehydration.

The perils of overhydration in athletes are now well known.2 In the 1990s, coincident with the water trend, some US insurance providers stopped compensating for measurement of the third electrolyte, chloride. It was dropped from some standard panels of laboratories. Hypochloraemia, although as common as polydipsia, is under-reported, and can result in fatigue, irritability, and cramps. Additionally, Decaux3 questions the long-held presumption that mild hyponatraemia is asymptomatic: sodium concentration of about 128 mmol/L is associated with falls probably caused by impairment of attention, posture, and gait mechanisms. Some football coaches and professional golf and tennis players take a salt tablet as a fast-acting cure for a cramp. We drink water and thus dilute sodium and chloride, which are abundantly lost in the form of sweat, causing more cramps. Athletic associations and the US military4 now advise against drinking too much fluid, because hyponatraemia was noted in 10-15% of marathon runners.5 Water stations have been cut in half in major marathons.

Correction of hyponatraemia too rapidly causes brain injury. However, patients with high blood urea, specifically those with kidney failure or on dialysis, tolerate such fluxes of volumes and ions. They are less susceptible to osmotic demyelination.6 Urea helps modulate the solute shift. Urea production in the liver combines carbon dioxide with ammonia. In the human kidney, urea, which is highly water soluble, allows formation of hyperosmotic urine through the countercurrent system. Regulated by antidiuretic hormone, urea concentrates in the medullary interstitium then flows back into the tubule, preventing excessive loss of water and sodium. In Belgium, urea is infused with solute in cases of severe sodium depletion.6 Addition of urea to sports drinks needs to be studied; this might be an organic solution for the hyponatraemic athlete.

Not everyone lacks sodium in everyday life. Compounding our calorie-free excessive fluid consumption is ubiquitous sodium content in the diet: sodium bicarbonate, monosodium glutamate, sodium phosphate, sodium carbonate, sodium benzoate, and sodium chloride.7 Even before the addition of preservatives, meat is rich in salt. Pre-Columbian native American hunting tribes were carnivorous and neither traded nor sought salt, whereas herbivorous agricultural tribes did. Some vegetarian animals crave salt licks and we used that fact to our advantage to domesticate them.8 Generally, carnivores do not need supplemental salt.

Some people need more water than others, such as those with kidney stones,9 with an iodine load, in case rhabdomyolysis occurs, or when taking specific drugs. Moreover, gastrointestinal loss should be attended to, particularly for young, elderly, or frail people. Robust Pakistani soldiers who belong to high-altitude mountain tribes have a naturally raised haemoglobin concentration. When they are sent on manoeuvres in the hot and dry Saudi desert, they can have cerebral ischaemia as a result of haemoconcentration. People in Saudi Arabia who live at low altitude with a lower baseline of haemoglobin than those who live in high altitude fare better.10 Their Pakistani counterparts, however, need to remember to drink more fluids.

Is fluid consumption a treatment for constipation? Lindeman and colleagues11 interviewed 883 elderly (average age of 74 years) men and women and found that fluid consumption had no effect on constipation. Chung and colleagues12 noted that an increase in fluid intake (isotonic or free water) did not significantly change stool output. However, urine output increased significantly. A consensus recommendation is that fluid neither shortens colon transit time nor determines bulk of stool.13

Drinking fluid has been recommended for airline passengers. Landgraf and colleagues14 showed that passengers gain an average of 1 kg of weight in water during a simulated 12-h flight. In four of four experiments, fluid intake exceeded renal excretion during the simulated flight, when the large capacitance veins of the pelvis and thighs are put to task. There is an analogy in the operating room; Coleridge-Smith and colleagues15 elegantly observed that the diameter of veins in a leg is proportional to fluid received during surgery. Patients who received 1 L of fluid had 57% vein distension compared with 22% in the control group. Comerota and colleagues16 found radiofibrinogen-detectable deep-vein thrombosis after venous distension in excess of 20%. Of 21 patients undergoing hip surgery, 11 developed postoperative phlebitis. The average dilation in those 11 patients was 29%, and only 11% in the uncomplicated group.17

We might put away our pocket calculator and rely on a powerful computer of variables: our brain, represented by thirst on one end, and very little preventing a patulous mouth from over-imbibing on the other. Pushing fluid is a faulty recommendation amplified by an urban legend since the early 1990s.
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am

Re: How many glasses of water a day?

Postby JeffN » Fri Dec 21, 2012 7:44 am

More support for thirst being the best measure..

In Health
Jeff

http://www.nature.com/ejcn/journal/v66/ ... 2157a.html

Origins for the estimations of water requirements in adults
European Journal of Clinical Nutrition (2012) 66, 1282–1289; doi:10.1038/ejcn.2012.157;

Abstract

Water homeostasis generally occurs without conscious effort; however, estimating requirements can be necessary in settings such as health care. This review investigates the derivation of equations for estimating water requirements. Published literature was reviewed for water estimation equations and original papers sought. Equation origins were difficult to ascertain and original references were often not cited. One equation (% of body weight) was based on just two human subjects and another equation (ml water/kcal) was reported for mammals and not specifically for humans. Other findings include that some equations: for children were subsequently applied to adults; had undergone modifications without explicit explanation; had adjusted for the water from metabolism or food; and had undergone conversion to simplify application. The primary sources for equations are rarely mentioned or, when located, lack details conventionally considered important. The sources of water requirement equations are rarely made explicit and historical studies do not satisfy more rigorous modern scientific method. Equations are often applied without appreciating their derivation, or adjusting for the water from food or metabolism as acknowledged by original authors. Water requirement equations should be used as a guide only while employing additional means (such as monitoring short-term weight changes, physical or biochemical parameters and urine output volumes) to ensure the adequacy of water provision in clinical or health-care settings.
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am

Re: How many glasses of water a day?

Postby JeffN » Thu Jun 27, 2013 7:35 am

And one more, even for athletes. ..

Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure
Br J Sports Med 2013; 47 : 679-686

Review
Abstract

Objective: It is purported that exercise-induced dehydration (EID), especially if ≥ 2% bodyweight, impairs endurance performance (EP). Field research shows that athletes can achieve outstanding EP while dehydrated > 2% bodyweight. Using the meta-analytic procedure, this study compared the findings of laboratory-based studies that examined the impact of EID upon EP using either ecologically valid (EV) (time-trial exercise) or non-ecologically valid (NEV) (clamped-intensity exercise) exercise protocols.

Methods: EP outcomes were put on the same scale and represent % changes in power output between euhydrated and dehydrated exercise tests. Random-effects model meta-regressions and weighted mean effect summaries, mixed-effects model analogue to the ANOVAs and magnitude-based effect statistics were used to delineate treatment effects.

Main results: Fifteen research articles were included, producing 28 effect estimates, representing 122 subjects. Compared with euhydration, EID increased (0.09±2.60%, (p=0.9)) EP under time-trial exercise conditions, whereas it reduced it (1.91±1.53%, (p<0.05)) with NEV exercise protocols. Only with NEV exercise protocols did EID ≥ 2% body weight impair EP (p=0.03).

Conclusions: Evidence indicates that (1) EID ≤ 4% bodyweight is very unlikely to impair EP under real-world exercise conditions (time-trial type exercise) and; (2) under situations of fixed-exercise intensity, which may have some relevance for military and occupational settings, EID ≥ 2% bodyweight is associated with a reduction in endurance capacity. The 2% bodyweight loss rule has been established from findings of studies using NEV exercise protocols and does not apply to out-of-doors exercise conditions. Athletes are therefore encouraged to drink according to thirst during exercise.
JeffN
 
Posts: 5490
Joined: Tue Jan 08, 2008 4:56 am


Return to Jeff Novick, RD

Who is online

Users browsing this forum: No registered users and 3 guests