It's clearly true that over the long term, calories taken in will be roughly equal to calories burned, minus a tiny delta reflected in weight change. However,

It's clearly true that over the long term, calories taken in will be roughly equal to calories burned, minus a tiny delta reflected in weight change. However, what the parent is asking is whether we know that the longevity effect is due to persistently low calorie intake (which will result in lower body weight, so that an equilibrium can be reached that's sustainable at that lower caloric intake), or if instead it might be sufficient for the body to receive intermittent signals of caloric deficit. Personally I don't know the answer to that question; I'm not sure if it is yet known.