salt and vinegar

why the exchange of fat-containing foods with fat-substitute-containing foods would not be ideal for a marathon runner

There is not a substitute for water when baking or cooking foods. There are a lot of things you can use to substitute water intake in your diet though. Anything you make with water including tea, lemonade, hot tea, coffee, or hot chocolate.

Metamucil should not be taken as a substitute of eating high fiber foods. However, if you have a diet low in fiber, Metamucil can be a supplement for your diet.

For Swimming Pools, salt is used as a substitute for chlorine.