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).
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).
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
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).
Hydration and health
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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