I looked at the xml files to see if I could figure out how the hunger system works. Apparently, it is not using stamina that consumes food, but regenerating stamina that consumes food.
From entityclasses.xml:
<passive_effect name="HealthChangeOT" operation="base_set" value="0.017" /> <!-- heal 1 point of (red) health / minute -->
0.017 HP/Second * 60 Seconds/Minute = 1.02 HP/Minute, this seems simple enough.
<passive_effect name="StaminaChangeOT" operation="base_set" value="10" />
If this works on the same scale as health then:
10 Stamina/Second * 3600 Seconds/Hour = 36,000 Stamina/Hour = 36,000 Stamina/standard in-game day
<passive_effect name="StaminaLossMaxMult" operation="base_set" value="0.0068"/> <!-- regening stamina costs food, blacks out the stamina bar -->
36,000 Stamina/Hour * 0.0068 Max Stamina lost/Stamina regenerated = 244.8 Max stamina lost/Hour.
You can theoretically lose a maximum of 244.8 food point in a single default length day.
I then did my own tests, where I just jumped continuously in the same spot for four in-game hours (jumping directly subtracts 20 stamina and doesn't affect regeneration), and my character consumed 45 food and 49 water. If you extrapolate that over 24 hours, you could theoretically consume 270 food and 294 water. I'm just going to ignore this test for my final calculations though.
According to this arbitrary article, peak performance is burning 12,000 calories a day. I'm assuming that peak performance does not allow for sleeping.
If we assume that endlessly jumping in the same spot is peak in-game performance, then each unit of food is equivalent to 49 calories. One unit of grilled meat is therefore 490 calories.