Calorie counts are better, but still gloss over all the nutritional differences between e.g. beef and carrots. Comparing ingredients piecemeal when they aren't

Calorie counts are better, but still gloss over all the nutritional differences between e.g. beef and carrots. Comparing ingredients piecemeal when they aren't nearly perfect substitutes doesn't make very much sense. If you reduced your meat intake by 1kg of beef per week or month, what would you replace it with to sustain your nutrition? It seems like it would be a fairer comparison to drum up reasonable examples of complete vegetarian, vegan, and omnivorous diets and work out a carbon footprint (or whatever ecological impact measure you prefer) of each backwards, from the plated food back to the source. Then look at the complete diets that have the lowest impact. I would still expect that vegan, vegetarian and very low-meat diets would do better than the typical diet in the US.