Post treatment: What to expect next? What role does diet play?

OK, it ‘feeds’ cancer….but if you do a simple search on glutamine it is one of most ubiquitous of the non-essential amino acids. (I erred when I inferred it was a nucleic acid).
Not only is it found in too many foods to mention (including all proteins, many vegetables,etc), it is used in almost every single function in the body from immune support to muscle function and digestion and absorption.
You really cannot live in a state of health without it. However, because it can also be converted to glucose in times of starvation or other low glucose situations, the speaker in that video is stating that along with glucose, it too feeds cancer.
However, he FAILS to mention gluconeogenesis - another pathway by which lipids and even ketones (the Atkins gold standard) can ALSO be converted to glucose, so trying to focus on glutamine will only get you so far.
Our bodies are incredible organisms which have evolved to survive. Unfortunately, cancer hijacks our survival mechanisms and uses THEM to survive. It is not easy to deal with - certainly not as simple as in taking this or eliminating that - and many times this tug of war eventually goes to one side or another.

Well, cancer cells have a high demand for DNA, as they are rapidly reproducing, and the DNA has to replicate itself every time it divides. OTOH, starving the rest of the body of the ability of cells to get what THEY need to replicate doesn't make much sense, either?