I'm sure this has been mentioned before but in case it hasn't, body weight is directly linked to calories in V calories out.

Basically, your body will burn X amount of calories if you do nothing other than stay alive (i.e in a coma), your body will burn Y amount of calories doing what ever your body does above X (i.e doing what ever you do in a day) and the things you consume are Z (food and drink) are less than X & Y combined.

You WILL lose weight if X+Y>Z

There's no "oh but I put on weight easily" no "my genetics"  if you consume less calories than your body burns in a day you'll lose weight. Exercise creates an energy defect hence increased weight loss.

You could eat only butter and lose weight providing you consumed less calories than you burned, I don't recommend it though as a deficiency will kill you eventually