Why can people last longer without food than they can without water? Food has water in it. Does this not factor in to survival?
In: Biology
Food doesn’t have enough water in it. The thing about calories are that they’re pretty fungible. If you don’t have enough of one particular energy source, the body has metabolic pathways to provide at least reasonable facsimiles. Our bodies are incredibly energy dense. If you’re 180 pounds and 10% fat you have 18 pounds of fat.
18 pounds of fat at about 3500 calories per day means you have over 60,000 calories in just your fat tissue. On a zero calorie input you could probably survive a month on that alone. Of course, other things start to break down and go haywire as you lose more adipose tissue but that’s just a really fit person. Someone with larger fat stores could go even longer.
Water on the other hand we go through about 2/3 of a gallon of water per day. We get about 40% of that through metabolism (some of the energy generation generates water) and water in food. The rest comes from water we drink.
We need water for a whole heap of biochemical processes because a lot of our enzymes that do things that let us live use hydrolysis. When ATP, your body’s molecular energy currency, splits to release energy it is hydrolyzed, or broken apart by water. Without water, we can’t even consume the energy we manufacture.
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