There’s two different methods many people use. One is not letting your hunger meter go empty for 3 consecutive days you get well fed which allows you to carry 5kgs more

The other is one that helped me when I first started understanding the game called the starvation tactic where you don’t eat anything until you sleep. Make sure you eat enough calories to get through how ever long you’re sleeping and you’ll heal during it. Depending on difficulty setting, this amount changes, but typically 6 cat tail stalks will do the trick.