This is a book-marking post for thoughts I had in https://www.facebook.com/TheFatEmperor/posts/1442430506020812.
"The human body does not need carbohydrates from an external food source, because it is capable of very precisely and correctly assembling its own amounts of glucose that is needed in very small amounts for auxiliary and specialized functions." - Igor Butorski.
1) It's not very precise. See http://nigeepoo.blogspot.co.uk/2012/04/how-eating-sugar-starch-can-lower-your.html
2) It's not enough to fuel high-intensity exercise. See http://nigeepoo.blogspot.co.uk/2011/02/funny-turns-what-they-arent-and-what.html
3) Using the above argument, the human body does not need saturated fats & monounsaturated fats from an external food source, because it is capable of very precisely and correctly assembling its own amounts of saturated fats & monounsaturated fats (out of carbohydrate) that are needed in very small amounts for auxiliary and specialized functions.
If we only consumed Essential Fatty Acids, Essential Amino Acids, Vitamins, Minerals, Fibre/Fiber, Water & Anutrients, there wouldn't be much to eat. Also, there wouldn't be a source of chemical energy to generate heat energy & mechanical energy. That's what dietary carbohydrates & fats are for.
Respiratory Exchange Ratio/Respiratory Quotient (RER/RQ) varies with carbohydrate & fat intake, as the body preferentially oxidises the fuel that's most readily available.
RER/RQ varies with Exercise Intensity.
Low-intensity exercise results in mostly fats being oxidised.
High-intensity exercise results in mostly carbohydrates being oxidised.
Medium-intensity exercise results in a mixture of fats & carbohydrates being oxidised.