Warning - Anecdata!!
In a single iteration, N=1 experiment, I found it doesn't work with potato:
Day 1 (Fresh boiled potato, mashed - eaten with cheese and marmite): Blood sugar - (Before) 5.4 (1hr) 7.6 (2hr) 7.7 (3hr) 4.9.
Day 2 (Reheated boiled potato, mashed - eaten with cheese and marmite) : Blood sugar - (Before) 5.9 (1hr) 12.0 - WTF?? (2hr) 8.1 (3hr) 5.4
Ergo - reheating yesterdays potato is, if anything, worse.