From "Notes On Rations, Supplements & Energy Metabolism"
Section: Weight (Food in terms of Energy per Gram)
During a trek, I'll burn approximately 6,000 kcals per day, yet only carry between 2000 and 2500 kcals of food. That 3500 to 4000 calorie deficit, after a few days begins to use up body fat stores. For the 2019 Summer Kit Test, my daily rations contained 2381 kcals (which is a little higher than normal) and this weighed in at 644g (at a calorie density of 3.70 kcal / gram). 644g / day = 6.4kg for the 10 day trek (Summer Kit Tests are normally a bit longer, but we had a lot going on).
The point here is simply this: food is heavy. The main reason we're carrying it is to provide some buffering against the inevitable drain of body fat stores. We want as much calorific bang for our buck (while not entirely sacrificing nutritional value) and this means energy dense foods. Which is why the most important number on the spreadsheet is calorie density. I try to keep this number between 3.5 and 3.8 kcals per gram.