One of the reasons I posted this is because I wanted more discussion on the topic of this paper. On the website, I didn't see much of a discussion happening. As in the comments here, it seems that the term coined for this is "ego depletion".

Recently I've noticed many articles on HN how sugar, carbohydrates, dieting, etc. affects the brain, gut, and overall human body. Ego depletion is now on my list of topics to research further because I want to know more about the human body. I always thought of my Kinesiology class in university to be important because it taught about the relationship between the health of the human body and its environment. I hope there will be more findings in the future so we can, in a sense, optimize ourselves. For example, based on this paper it seems that eating a snack when studying can lead to better processing information and staying focused.