[taneq]

Micronutrients, obviously not. You have to get your required vitamins and minerals etc. or you'll get sick. But for macronutrients (basically carbs/fats) then yes, basically. Maybe you'll be slightly more or less efficient with some types of food, but in the end, if you eat a calorie you have to burn a calorie or you'll put on weight.

The key factor is to realise that it's relative to your body. Maybe for you, personally, a gram of fat is more efficiently metabolized than a gram of carbs. Whatever. You have to close the loop.

If you're above your target weight, eat progressively less until you start losing weight, then maintain that intake until your target weight. If you're below your target weight, eat progressively more until you're gaining weight, then maintain that intake until your target weight.

[nradov]

For a given level of energy output, metabolizing fat requires more oxygen than metabolizing carbohydrates. There are some minor individual differences in efficiency but the basic relationship is true for everyone. That's why you don't see low-carb diets consumed by athletes who compete at the top levels of sports in which VO₂max is a limiting factor.

[headsoup]

What if you're gaining fat instead of muscle? I think your version only works if the only metric required is purely -Kg over time, and doesn't factor in anything else that people might want to call it 'healthy weight loss/gain.'

[taneq]

OK, so which goalposts would you like us to aim for here? If you want to be healthy, eat a balanced diet. If you want weight loss, then eat less food than you burn, using a feedback loop to adjust our dietary intake. If you want fitness, do some cardio. If you want strength, lift some weights. If you want all of these things, then do all of these things.

[headsoup]

The goalpost that is in some way meaningful, which adjusting total consumption of 'whatever' for the sake of purely moving a number up or down isn't.