Even if we reach a point where 100% of the edible parts of food available are used, there will always be 'waste' byproducts. Stalks, skins, peels and pips are usually discarded into regular waste streams after a meal is finished.
A few years ago, I helped to organise an event at which Prof. James Clark came to speak and was reminded of his talk by this challenge. He is a leading green chemist who heads the Green Chemistry Centre of Excellence and helped to found the Orange Peel Exploitation Company (OPEC), saying:
"In Brazil, the world’s largest producer of orange juice, half the orange fruit is left as waste once the juice has been recovered. This corresponds to three million tonnes a year of orange peel that can be used to produce chemicals, materials and fuels."
This is just one great example of the cool science that green chemists carry out, driven by the vision of a 'closed loop' product lifecycle where all the waste is recovered and reused. Increasingly, there are attempts to push industry and governments to pursue green chemistry initiatives. The GCCE Twitter page posts links to many of the latest developments in the field.