Agreed, this is nonsense. Macronutrient proportions will be more or less the same from culture to culture, but will be much more variable at the individual leve

Agreed, this is nonsense. Macronutrient proportions will be more or less the same from culture to culture, but will be much more variable at the individual level. It's micronutrients that are more likely to change more widely, due to different foods containing different amounts of them.