Caloric restriction for life or a short-term fast before surgery may have different physiological effects compared to ad libitum feeding.

“these animals were constantly at 70% caloric intake the next group was your control group and then your third group was ad libitum diet until two days before an operation at which point they were calorie restricted to a near fast and I'd have to go back and look I can't member if it was 24 or 48 hours of fasting it might've been a 24-hour fast 48 would be pretty extreme for mice so in summary you've got control there's straight-up eating you've got 70% or 30% CR forever and then you've got control and then fasted for a day”