That import figure for food / calories is a snapshot at the start of WW2 prior to rationing being implemented and not what occurred during the entire war. By 1945, the UK was producing 75% of the food they consumed.
Germany was 'self-sufficient' in food up until about 1942 for three reasons: 1) extensive plundering / requisition of food in occupied countries, 2) extensive use of poorly fed POWs to boost domestic food production & 3) Trade with the Soviets which came to a crashing halt on 22 Jun 1941.
The trend would continue downward as Germany was cut off from fertilizer, animal fodder, plus livestock were not being replaced as they were slaughtered due to lack of fodder.
With the Soviets still at peace from Germany, Germany could try to increase production by:
1) Diverting nitrogen production to fertilizer (possible without as many shells needed for the eastern front)
2) Diverting fuel and machinery to agricultural production (possible without vehicles driving all over the eastern front and not having to produce as many replacement tanks)
3) Diverting people to agricultural production, especially talented and motivated people (possible if they are not dying on the eastern front).
4) Expanding trade with other countries (really only possible with Turkey, across the Trans-Siberian with Japan, with French North Africa (a source of Fertilizer) or via 3rd party buyers, all of which is more possible with to some extent the Soviets neutral.
This seems possible, if Germany adopts a largely defensive stance against Britain (with the Soviets still at peace), to keep food production adequate, to keep a large armored force and air force on the defense in France (where they don't use fuel if they are not driving or flying around so much). Hope Britain tires of this low scale war and makes an acceptable peace.
This all breaks down if the USA comes in the war of course, but Germany controls that, all they have to do is encourage the French to resist the Japanese incursion into Indo-China, and the path to USA entry in the war is diverted.