The Gemara on the previous daf presents a discussion between Rava and Rav Naḥman regarding the case in the Mishna (70a) of the man who stole an animal from his father and killed it before his father died, who will have to pay four or five times the value of the animal to his siblings who are inheriting the estate together with him. Between their conversation in the evening and the next morning, Rav Naḥman changed his mind – and his ruling on the case. In explaining why he rejected the previous evening’s reasoning he said that he had not eaten meat of an ox the day before.
Rashi and the Ra’avad understand this statement as an expression indicating that he had not paid close enough attention to the details of the case. The Ra’avad suggests that the reference to “ox meat” was actually a hint to the case itself, which dealt with a question about paying back five times the value of an ox. Tosafot and others accept a simpler meaning – that since he had fasted that day he was weak, which affected his ability to learn. Similarly, Rav Avraham Neimark in his Eshel Avraham interprets the phrase in its clearest meaning – that he had not eaten meat or any other food of substance that day so he was unable to think clearly.
For proper brain function, the body needs to have certain elements present in the blood stream. Some of these elements are supplied by ingesting carbohydrates which are processed by the body and become readily available sugars; there is also a need for a certain level of proteins in the blood. When there is a lack of these elements – due to fasting or improper nutrition – brain function will be weakened. Thus, one approach to understanding Rav Naḥman’s statement is that since he had not eaten properly on the previous day, his thought processes were not up to their usual level of clarity and intensity.