Weight Loss and Drinking Water Myths Debunked

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I found several claims that up to 75% Americans are dehydrated *, and also kept meeting the guideline that we should drink at least 8 glasses of water a day. However when I looked a bit deeper I found no evidence base for the 8 glass guideline. 


Many claims that the population at large is dehydrated seem to be based on the 8 glass guideline, so their basis is questionable. 


Also no assessment or standard measurement seems to have been made for mild dehydration (1). 


What is certain is that I personally find it very irritating having to run to the bathroom every 10 minutes if I drink 8 glasses of water!


Numerous studies have shown increasing the amount of water you drink can help weight loss and maintenance (1).


Drinking water can increase the amount of calories you burn (2). 


In one study it was found that drinking 500ml of water increased metabolic rate by about 30% in men and women. 

The effect was noticeable within 10 minutes of drinking the water and was sustained for more than an hour. 


The authors of this study suggested that drinking 1.5 litres of water per day would lead extra energy expenditure of about 200kJ per day. 


Over a year energy expenditure would work out to around 73,000kJ or 17,400kcal which is equivalent to the energy content of around 2.4kg of adipose tissue (3) (4).


One study found that drinking 500ml of water per day lead to weight loss over the course of a year for a group of overweight dieting women, and this was without any diet or other changes. (5)


A further study found drinking an extra 1500ml (1.5litres) of water a day for 8 weeks (500ml of water 30 minutes before each meal) lead to decreases in body weight, body mass index and body composition in 50 overweight girls.(6


Another very similar study produced comparable results and reported the water suppressed appetite in addition to reducing weight and body fat.(7)


Other studies support the evidence that drinking water before meals can suppress appetite (8), with one finding drinking 500ml of water 30 minutes before breakfast reduced calorie intake by 13% (9). 


The effect seems stronger in older people than in younger ones (10).


Replacing other calorie-high beverages (soda, fruit juices etc) with water which is calorie free can have a big impact on weight loss (11, 12). 


In one study people who drank mostly water rather than other beverages consumed on average 194 fewer calories per day (13), or around 8% less calories overall (14). 




In another study in German schools involving almost 3000 children the risk of obesity was reduced by a staggering 31% where water replaced other beverages (15).


In reality everybody’s water intake requirements are different (16) based on variables like climate, weight and how active you are. 


What is clear is that drinking the additional 1500ml of water as 500ml 30 minutes before each meal does have science behind it, and has been shown to work in studies.


Hydration and performance

Physical and mental performance can be affected by hydration levels (17). 


Physical performance can be significantly impaired by even modest (-2% body mass) dehydration (18), as can performance in tasks that require attention, psychomotor and immediate memory skills and in the assessment of the subjective state (19, 20). 


When dehydration levels were at 2% of body mass and higher the impairment of mental function was much more profound (21). 


One study found that children’s memory was improved by drinking water (22). 


Dehydration has been found to negatively affect mood as well as cognitive ability (23, 24, 25, 26).



Hydration and health

There is evidence that high fluid intake levels are linked to significantly reduced risk of bladder cancer in men (22) and decreased risk of colon cancer in both men and women (23). 


Higher (5 or more glasses compared to 2 or less glasses per day) fluid intake may also lead to reduced risk of coronary heart disease (24).



But How to Remember to Drink it?

There are some free apps available to help you remember to drink water and keep hydrated. 


Some of them seem set on the arbitrary standard of 8 glasses a day, but others allow you to set the amount of water you plan to drink during the day like this one for IOS devices:


And this one for Android devices:


Article by Victoria Warrell

REFERENCES NOT AVAILABLE ONLINE:

* Survey of 3003 Americans, Nutrition Information Center, New York Hospital-Cornell Medical Center (April 14, 1998).






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