Where in our diet that water comes from has little relevance to its effectiveness at hydrating us and allowing the body to function. For most people, most of the water in our body comes from drinks, but a substantial proportion (typically about 20-30%) comes from the foods we eat; even foods that we think of as being quite dry (e.g., bread) can contribute a significant amount.
Studies that have measured the amount of water people consume have formed the basis of a number of recommendations; for example, the US Institute of Medicine (IOM)1 and the European Food Safety Authority (EFSA)2 have both recently published water consumption guidance.
The results of the studies that have monitored water intake show that there are very large differences in water and/or fluid intake in different individuals and in different populations. This has translated into differences in intake recommendations. In 2004, the IOM published adequate intake (AI) values for total water intake in temperate climates.1 This AI is water from plain drinking water, water in other drinks and water in food. The AI for total water for young men is 3.7 litres and for young women is 2.7 litres per day. These recommended intakes are based on intakes of generally healthy individuals who are adequately hydrated.
It is important to understand that people can be adequately hydrated at levels below as well as above the AIs provided. Due to the large variances in individual intake mentioned, people who consume less than the AI are not necessary consuming too little and people consuming above the AI are not necessarily consuming too much.
The recent recommendations produced by EFSA in 20102 are more conservative than the IOM values and are 2.0 litres per day for adult females and 2.5 litres per day for adult males. Similar to the IOM, EFSA’s values for total water intake include water from drinking water, beverages of all kinds, and from food moisture. They only apply to conditions of moderate environmental temperature and moderate physical activity levels.
As the amount of water that people need to consume for body hydration reasons is determined by the amount of water that people lose from their body, the environmental conditions in which people live, the amount and type of physical activity they do and their individual physiology will all influence how much water they need. Therefore, someone with a low water intake will not necessarily be dehydrated and someone with a high water intake will not necessarily be in water balance over hydrated.
Does exercise make a difference?
The assumption that people will need to consume more water just because they exercise is not always correct. If the exercise is high intensity or long duration and causes significant sweat loss, then there is a good likelihood that they’ll need more water.
But if someone already consumes more water than they absolutely need when not exercising, then they may not need to increase their water intake to account for extra sweat water losses during exercise.
Water losses during short exercise sessions can be easily estimated by weighing yourself immediately before and immediately after the activity. If bodyweight is lower at the end of exercising than at the start, water has been lost from the body. The amount of water that has been lost (or gained) can be calculated as approximately one kilogram weight change for each litre of water change.
This feature was first printed in the May/June 2012 issue of Fitpro magazine.
To view the references related to this article visit www.fitpro.com/references
The views and opinions expressed in this article are those of the author and not of Fitness Professionals Ltd or Virtual Magazine. Consult a qualified health or fitness professional before making changes to your diet or exercise.