I'm interested, is there anything that I can eat that would be endothermic when digested? Preferably that also wouldn't kill me were I to eat it.
Thank you Jim, thread closed.IMO, this is an old wives tale - in other words largely not close to factual. Foods are defined as a source of nutrition. Non-nutritive "food" makes very little sense. You are asking: is there some food I can eat that uses more calories to process (digest) than the food provides. Short answer: no.
Water, crushed ice does what you want - provides no energy. And DO NOT believe the garbage out there on the internet - miracle foods and super foods do not exist. Really.
Eating less than 600 kCal of food daily, except under medical supervision, is a great way to get in serious medical trouble. Ask your physician for guidance, we do not provide that here.
A better answer - increase your level of activity. By a large factor. Burn more calories than you consume. How do you do that - ask a health professional, not us.