You're mixing two different arguments together. Calories in/out is the only requirement for weight loss. Calories in/out is a percentage of the overall picture

You're mixing two different arguments together. Calories in/out is the only requirement for weight loss. Calories in/out is a percentage of the overall picture we define as "health". To lose weight, you only have to be at a caloric deficit. You can eat _only_ three cupcakes a day and probably lose weight (unless they're kinda insane cupcakes). If you only eat 3 cupcakes a day and nothing else, you will be malnourished and nutrient deficient, which I would extend to mean "unhealthy", but you will lose weight.