My thinking about temp basals has changed since I've been living with a continuously variable basal system. Before hooking up to my current Loop set-up, I had a hard time believing that a temp basal rate could have any influence in the short term.
My Loop system shows my BG trace from the present time and back several hours. It also shows a projected BG going out for four hours. I've watched time and again as Loop makes a temporary basal change. At first I thought that the projected BG line at about two hours and more would change, but not the near-term zero to two hours out. I do often see the near term forecast BG respond to basal rate changes. I found this puzzling since I know my insulin, Apidra, does not peak for 60-90 minutes.
While the insulin does not peak for an hour or more, its onset is 15-20 minutes. How can the onset of insulin action move a strongly trending BG line? The answer, to my understanding, is that it can't. But what about a lightly trending BG line, whether flat or slowly moving up or down?
If my blood glucose is well balanced, then even a small force, like the insulin action temp-basal onset, can move the direction of near-term BG trend. I think of it like one of those finely tuned balance scales. If you place exact weights on both sides, the scale balances. If you add even a small amount of weight on either side, the scale tips in that direction. So, if your BG trend is nearly balanced, then I think temp basal changes can exert significant influence.
Well, that's my theory.