26/05/2010
Dr. Michael McCoy

Water - supermodels apparently drink buckets of it every day. But is there any basis in fact behind the two litres of water a day mantra?

Not if you ask Professor Heinz Valtin. According to a report published in the American Journal of Physiology, the good professor spent 10 months trawling through existing research and couldn't find any evidence that we need to chug down two litres (just over 4 pints) a day.

A wellspring of sources

Despite this, the professor doesn't argue that we don't need two to 2.5 litres of water per day. What he does say is that much of our daily requirement for the wet stuff can flow from other foods and drinks. No matter what the supermodels say, it doesn't all need to be water.

Solid foods such as fruits and vegetables contain lots of water. To pluck but one example, your average lettuce is mostly water.

Exceptions to rules

The two litres a day formula also ignores lifestyle and environmental factors. If you're a marathon runner, or the temperature is closer to 100 than 50, the chances are that two litres just won't be enough.
Water: Does Two Litres A Day Pay?



26/05/2010
Dr. Michael McCoy

Water - supermodels apparently drink buckets of it every day. But is there any basis in fact behind the two litres of water a day mantra?

Not if you ask Professor Heinz Valtin. According to a report published in the American Journal of Physiology, the good professor spent 10 months trawling through existing research and couldn't find any evidence that we need to chug down two litres (just over 4 pints) a day.

A wellspring of sources

Despite this, the professor doesn't argue that we don't need two to 2.5 litres of water per day. What he does say is that much of our daily requirement for the wet stuff can flow from other foods and drinks. No matter what the supermodels say, it doesn't all need to be water.

Solid foods such as fruits and vegetables contain lots of water. To pluck but one example, your average lettuce is mostly water.

Exceptions to rules

The two litres a day formula also ignores lifestyle and environmental factors. If you're a marathon runner, or the temperature is closer to 100 than 50, the chances are that two litres just won't be enough.

And if you're consuming excessive levels of water-depleting diuretics, such as caffeine or alcohol, you might need extra fluids to top up your tanks.

How much is enough?

In the 1980s, America's Food and Nutrition Board recommended a 'process' based approach to managing water consumption. The board suggested we swallow one millilitre of water for every calorie consumed. But while this formula cleverly matches our thirst to energy expenditure it contains a fatal flaw. Most of us wouldn't have a clue how many calories we consume in a day.

Another option might be to adopt an 'outcome' based approach. If you monitor your urine and aim for 'output' the colour of weak apple juice you've probably got the balance about right.

In general, the two litres of water a day target isn't a bad idea. Sometimes you won't need that much, other times you might need more. What this mantra does do is remind us that water is a better option than soft drinks, alcohol or other fluid choices that can too easily deliver unwanted calories.
And if you're consuming excessive levels of water-depleting diuretics, such as caffeine or alcohol, you might need extra fluids to top up your tanks.

How much is enough?

In the 1980s, America's Food and Nutrition Board recommended a 'process' based approach to managing water consumption. The board suggested we swallow one millilitre of water for every calorie consumed. But while this formula cleverly matches our thirst to energy expenditure it contains a fatal flaw. Most of us wouldn't have a clue how many calories we consume in a day.

Another option might be to adopt an 'outcome' based approach. If you monitor your urine and aim for 'output' the colour of weak apple juice you've probably got the balance about right.

In general, the two litres of water a day target isn't a bad idea. Sometimes you won't need that much, other times you might need more. What this mantra does do is remind us that water is a better option than soft drinks, alcohol or other fluid choices that can too easily deliver unwanted calories.