I'm VERY sorry for your personal dietary issues, but I think you go too far in giving unhealthy lifestyles a pass. This is understandable from your perspective, but I will push back on a couple of points.

True: A calorie is a unit of energy, independent of the souce. Also true: In terms of general health and nutrition it is very important where a majoriy of a person's calories come from. A calorie from olive oil is pure fat and will be used very differently by the body compared to a calorie from lentils, rice or green beans. You need fat for sure, but not much. In general, particularly in the west, people get far too many calories from fat and starchy carbs far too few from vegetables (fibrous carbs).

Also mostly in the west, with our more sedentary lifestyles and shitty corporate-dominated food industry (particularly in the US), being thin is usually the result of a conscious decision to pay attention to what and how much goes in your mouth. Your situation is a very special and unplesant exception.