This part is interesting in light of the recent podcast about the Salt Fix.
Both muscle and liver showed increased ketone body content. This finding suggests that liver switched pyruvate substrate utilization from energy-intense gluconeogenesis to energy-neutral ketogenesis and thereby reprioritized its energy expenditure in favor of urea osmolyte production. https://www.jci.org/articles/view/88532/version/4/pdf
Also, in the original astronaut finding, the low salt diet contained 6g/day, and the high salt was 12g/day. They also saw some muscle breakdown for nitrogen to induce more urine at 12g, which likely explains the hunger at those levels. They were on a carb rich diet no doubt, too.
Yet another reason to get 5-7g of salt/day.