There are at least three other possibilities that come to mind immediately:
1) Restrict food sources to eliminate independence from the commercial food industry, i.e. to require you to continue to spend your money (esp. hyperinflated money) on food — this helps to keep you “in the system” as a wage slave)
2) Cripple resistance when TSHTF (think “Siege of Leningrad”).
3) Restrict food sources to eliminate them as possible barter items when TSHTF, esp. hyperinflation, or currently as part of the underground economy.
I leave the possibility of mass poisoning and/or drugging via “official” food sources as a matter for others to argue.
The oligarchy declared long ago in their own writings and arrogant pontifications that
THEY WOULD
USE
FOOD
AS
A WEAPON.
They meant it then.
They mean it now.
This is just much closer to implementation of those long held plans . . . of population reduction and culling the useless eaters out of the slave population.