Posting my suggestion for realistic Values and also Looking for suggestions on realistic Values. Fyi i'm using https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2907834593&searchtext=calories that fixes walking so its 40% the calories as running the same distance (not sure if the mod works)

As a test I played Louisville stumblers, with a survivor that was of medium weight, female (there's a mechanic for female survivors using different calories then males but atm its disabled) with lvl 5 on every stat / skill and used a mid 2h nailed baseball bat and spent most of the day sprinting, sitting on the ground when tired and killed 100 - 130 zombies on 3 playthroughs where i sprinted until exhausted, climbed a tall wall 4 times, and lifted a tv + chair to a random house (just to use the overburden stats) and using debug mode for to help count my calories

Idle 0.9
Walking 1.0
Running 1.2
Sprinting 1.3
Sitting 0.8
Overburden 1.3 (Imagine moving furniture / warehouse work)

Now during the most intense work killing and running almost the entire time, i compare my survivor to a navy seal more or less during hell week, your survivor is carrying a backpack full of loot, they're usually running everywhere like a madman and pushing exhaustion through zombie hordes. My character burned 6200-6600 Calories during my test. Doing 15 mins of research Navy Seals during training burn around 6000 calories on average and this reflects on my test which is close to the default settings. HOWEVER this is the average of a navy seal, during hell week Navy seals burn 8000+ Calories a day, Professional Athletes burn around 10,000 which i say compares with your survivor, with some sources claiming it can be up to 10,000-15,000 for both seals and Athletes. If you want extra realism i'd suggest Running 1.5, Sprinting 1.7, Overburden 1.5.

The potential problem: If your survivor is killing 200+ zombies late game day to day they're realistically pushing 8000+ Calories daily with all the work it takes to do that. However with mods i play with like Harder Fishing / Harder Farming / Harder Forging which makes fishing and forging impossible during winter with colder winters and longer lasting summers so sustainable Calories are a bit harder to come by. I should note I tested in normal weather conditions and in game your character burns more calories in the cold just like in real life in Navy Seals hell week training. Going around checking low loot setting, food averages on the lower side of 1700-3300 Calories worth of canned and preserved foods only, with houses containing 1000- and 4000+ worth of food being rarer, mods like pomp's foods, duff beer, sodas (with no 12 packs) and All American Apocalypse may interfere with my calorie averages but not by that much. As someone that's survived late game several times I find that overtime at low loot spawn you'll need to loot 2.5 houses a day just to keep yourself, and eating in itself is a chore, iv completely abandoned cooking outside of managing happiness and rping once in awhile. Its manageable but you do need to take time out of your day just to down 5 low calorie cans 3 times a day. Keep that in mind if you're aiming for late game survival. f you have modded towns you should be good for about 2 years of rampaging, but i'll get harder from there, just food for thought again eating will a chore you're playing with (imo) realistic 10,000 daily Calorie intakes.