We Asked Five Experts
By ALEXANDRA HANSEN, THE CONVERSATION
Everyone knows humans need water and
we can’t survive without it. We’ve all heard we should be aiming for eight
glasses, or two liters of water per day.
This target seems pretty steep when
you think about how much water that actually is, and don’t we also get some
water from the food we eat?
We asked five medical and sports
science experts if we really need to drink eight glasses of water per day.
All five experts said no
Here are their detailed
responses:
Karen Dwyer – Nephrologist
You only need to drink to thirst.
The best gauge of your hydration level is the color of your urine. You should
aim for light yellow in color; if very dark then you’re dehydrated and need
more water; if clear (like water) then you don’t need so much water. Excessive
water intake can be dangerous, particularly in those with heart conditions. The
kidney has a remarkable ability to concentrate water so if you are “getting
dry” the kidney will concentrate the urine and send a message to the brain to
drink more.
Vincent Ho – Gastroenterologist
No, it’s not necessary to drink
eight glasses of water a day. It appears the origin of the recommendation to
drink eight glasses of water a day may have come from a publication by the
National Academy of Sciences Food and Nutrition Board in 1945 stating “A
suitable allowance of water for adults is 2.5 liters daily in most instances.”
The recommendation also stated that
“most of this quantity is contained in prepared foods,” a fact which is often
overlooked. We do get a lot of our water intake from the foods we consume.
Cauliflower and eggplant for example are 92% water. A one-size fits all
approach is unlikely to be helpful. Healthy adults may not need to drink an
additional eight glasses of water a day. On the other hand, persons with
certain diseases or living in very hot climates may require larger intakes of
fluid.
Michael Tam- GP
Eight glasses, which is just less
than two liters of water, is very roughly the basal water required by a
fasting, well adult per day, who is doing nothing at all (for example, staying
in hospital), with no special losses (such as vomiting or diarrhea). In
day-to-day life, we usually have additional losses (exercise, or sweating
during a hot day), and we receive water from other sources.
There are the obvious ones from our
diet such as beverages, and juicy and moist foods, such as fruit and
vegetables. Less obvious is water from the metabolism of food. The conversion
of fats, carbohydrates, and proteins to energy in our bodies all produce water.
Rather than focusing on the number of glasses, simply drink fluids when
thirsty. Aiming for more water (especially in place of sweetened drinks) is
often a good idea to improve health.
Jon Bartlett – Sport Scientist
A person’s daily water requirements
are highly individual and dependent upon a number of internal and external
factors. While eight glasses of water per day is recommended as a base
requirement to meet daily physiological needs, the actual volume of water
required in a day is dependent on one’s day-to-day activities, health, and the
climate in which they reside.
Research shows even just a mild
level of dehydration can negatively affect both mental and physical
performance. This is further accentuated for individuals who are highly active
and who live in hot environments.
A simple and easy reminder to ensure
you are drinking enough is to drink to thirst, and for days when activity
levels are higher than normal or in hotter environments to increase the
regularity of drinking and the total volume.
Toby Mundel – Exercise
Scientist
Many factors will determine how much
water (via all foods and fluid, not just water!) your body needs. These include
body size and composition (weight, muscle, and fat), how much you sweat
(physically active, hot or humid environment, too much clothing) or urinate
(taking certain medication, being at high altitude), your health (having fever,
vomiting or disease) or status (pregnant, breast-feeding), and diet (high-water
content foods, carbohydrates).
For most healthy adults rarely
feeling thirsty and having light yellow (or colorless) urine usually confirms
adequate water intake. Other helpful tips include drinking a glass of low-calorie
fluid before and with every meal (to distinguish hunger from thirst), and
drinking low-calorie fluid before, during and after physical activity
(especially if you sweat). Although rare, drinking too much fluid can also have
negative health consequences so more is not necessarily better.
Written by Alexandra Hansen, Deputy
Editor and Chief of Staff, The Conversation.
Interviewed:
- Jon Bartlett – Sport Science Research Fellow, Victoria University
- Karen Dwyer – Deputy Head, School of Medicine, Deakin University
- Michael Tam – Specialist General Practitioner, and Conjoint Senior Lecturer, UNSW
- Toby Mündel – Associate Professor, School of Sport, Exercise and Nutrition, Massey University
- Vincent Ho – Senior Lecturer and clinical academic gastroenterologist, Western Sydney University
This article was first published
in The
Conversation.