This is actually a very simple problem to solve, add more fat to your diet. Nuts have 150-200 calories per ounce. They're low in saturated fats which are what will make you feel more sluggish and do not process as well and high in mono and polyunsaturated fats which metabolize more like carbohydrates. Experiment with adding different amounts into your calorie intake while hiking and learn what ratio of calories from nuts or trail mix works best for you. Everyone's body metabolizes food differently. Search for foods that are 140 calories per ounce or higher, there are more out there than you think.
My pack generally weights 25lbs on a 4-5 day trip with no resupply(29lbs if I have my camera gear with me), this is including all my food and 100oz of water in a camelbak bladder. I eat trail mix with high nut content all day and honey stingers(150-160 cal per oz) to snack on then Good To-Go dehydrated meals for dinner usually. Granted I know this will not work for everyone but it works for me and it still allows me to consume about 2500 calories a day without carrying a ridiculous weight in food. Plus I love trail mix so there is no trade off in enjoying food for me. 2500 calories weights about 1-1.2 lbs with what I eat.
Out of curiosity what is wrong with your knees? It might be more advisable to try and figure out and fix the actual cause of your pain versus just lighten your pack.
Edited by Adventurejus (11/13/17 08:54 AM)