Energy, or ENG as it is known in SCUM, is one of the four core factors that players need to keep tabs on if they want to survive. This is alongside Health, Stamina, and Dehydration.
Keeping your ENG levels high are vital to survival. The less energy you have, the slower you become, making you an easy target for other players and hostile NPCs.
To raise the ENG bar, you need to eat a surplus of calories, foods, and drink a lot of water to keep your stomach full.
ENG won't rise instantly. You'll have to wait for your character to digest to meals gradually over time. Foods like candy will digest quickly while meats could take longer.
You can keep tabs on what kind of foods you need to eat, as well as how many calories you are in-taking and using, in the top right column on the Metabolism page. You want to ideally have protein, carbs, sugars, water, and far above 20 percent at all times to rise your ENG.
You'll also want to ease up on activities that will burn calories fast, such as running and using stamina. Walking slowly to places is an ideal way to regain ENG, so have some patience.
Some players believed in the past that it was just the amount of food that you ate, trying to force their character to eat more than their body could digest. This just resulted in the character getting ill and having to puke the excess out.
Obviously all this eating will have an adverse effect on your character, so releasing your bladder or colon volume by going to the bathroom will also be required. Try not to have more than 120 percent of stomach volume and you should be fine.
While ENG should rise most of the time, the game is still incredibly buggy. Some players have expressed on Reddit that energy still doesn't rise after completing these actions, so let's hope that the developers fix the issue as soon as possible.