is no magic number in prescribing the amount of water to consume
throughout the day. The optimal amount varies according to body
size, activity level, environmental factors, and diet. Drink
just enough water throughout the day so your urine is clear.
Drink extra water before, during and after physical activity
or being exposed to higher temperatures. The goal is to drink
before you get thirsty.
If physical activity last longer than 90 minutes (eg: sports
competition), choose a sports drink with electrolytes. For even
longer durations, consider a beverage with electrolytes, carbohydrates
and protein or amino acids.
Dr Tim Noakes, MD, DSc, veteran of more than
70 marathons and ultra marathons and author of Lore
of Running (2003) makes the following recommendations:
- Drink according to your thirst, your body will tell what
- Dehydration will not contribute in any way to any illnesses
associated with prolonged exercise, including marathon, ultramarathons,
- There is no need to increase sodium above what your appetite
dictates, even during exercise.
- If you are carbohydrate adapted, you should ingest some carbohydrates
to optimize your performance during prolonged competitive events.
- Understand that much of what you believe about your personal
well-being is the result of targeted manipulations by industries
whose principal focus is their commercial fitness and not necessarily
your health or safety.
In addition, Noakes (1988) demonstrated that exercise intensity,
not the level of dehydration, is the most important factor determining
hyperthermia. His studies demonstrate that during prolonged exercise
in mild environmental conditions, a fluid intake of 0.5 l.h-1
will prevent significant dehydration in the majority of athletes.
Noakes T (2012). Waterlogged,
The Serious Problem of Overhydration in Endurance Sports.
Noakes TD, Adams BA, Myburgh KH, Greeff C, Lotz T, Nathan
M. (1988). The danger of an inadequate water intake during prolonged
exercise. A novel concept re-visited. Eur J Appl Physiol Occup
Also see Dr Noakes, video presentation Challenging
Beliefs, where he talks more about water requirements during
Hyponatremia, or water intoxication is a potentially fatal
condition caused by consuming too much water. Excessive water
consumption causes low sodium levels in the blood. Symptoms may
include nausea, muscle cramps, coma, and even death. A runner
died from the condition following the 2002 Boston Marathon. Another
runner was in a comma for 4 days following a marathon in Jamaica.
Effects of Dehydration
Dehydration of 3% of body weight can cause a 10% strength
loss and 8% speed loss.
Cold water is absorbed faster in the body; sugar slows absorption.
Effect on Metabolic Rate
Drinking 500 ml of water increased metabolic rate by 30% in
healthy, normal-weight subjects. The increase of metabolic rate
occurred within 10 min and reached a maximum after 30-40 min.
About 40% of the thermogenic effect originated from warming the
water from 22 to 37 C. The total thermogenic response was about
24 Calories. It was estimated that drinking 2 liters of water
per day would augment energy expenditure by approximately 96
Boschmann M, Steiniger J, Hille U, Tank J, Adams F, Sharma
AM, Klaus S, Luft FC, Jordan J. (2003). Water-induced thermogenesis.
J Clin Endocrinol Metab. 88(12):6015-9.
Also see Foods that May Aid
in Fat Loss.