The study doesn't try to say that big breakfasts are good or bad in general (it leans on previous works for that).
It's trying to determine the impact of the composition of said breakfast.
The full title of the paper is: "Big breakfast diet composition impacts on appetite control and gut health: a randomized weight loss trial in adults with overweight or obesity"
(I don't think "with overweight" is a great turn of phrase)
Buddha recommended to his followers a diet which consisted of a breakfast and a second meal at noon if needed. That is, for their health, primary meal early in the day and fasting the remainder. It's interesting that this advice seems fairly supported by science.
It was high fiber big breakfast vs high protein big breakfast.
(And no, this comment was not written by an LLM).