We can’t live for long without water. But our food is turned into water inside us – carbohydrates are metabolised to carbon dioxide and water. So could we live on dry biscuits alone?
• No, you can’t survive on the water produced during the breakdown of the carbohydrates in dry biscuits alone – a process termed catabolism. Theoretically, you could eat enough biscuits to provide the recommended 2 litres of water you need daily. But if we assume biscuits to be pure glucose – the end breakdown product of the starch found in flour – you would need to eat 2.4 kilograms of biscuit to get the required water.
However, carbohydrates can only be broken down when they are in an aqueous solution. So to make a thick biscuit porridge that the body could deal with (say 30 per cent solids by weight), the necessary 5.5 litres of water would need to come from you. In other words, you would need to put twice as much water in as you would recover from catabolism.
Generally, food is pretty wet –about 50 to 70 per cent water – which means you don’t need to supply much water from your body. But biscuits are dry, which is why people dip them in their tea before eating.
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We need a lot of other things besides water and carbohydrates to live healthily, of course: vitamins and minerals as well as salts, proteins and fats. So don’t try this experiment at home.
Simon Goodman, Griesheim, Germany
This article appeared in print under the headline “Internal reservoirs”
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