For what it's worth, the food selection heuristic I've been trying to follow which seems to work for me is a combination of:

- Try to maximize the ratio of protein to carbs in a food.

- For a given number of calories, look for foods with the highest amount of protein. Or somewhat equivalently, for a given amount of protein, look for foods with the lowest number of calories.

To me it feels like these allow me to reason about and compare foods without getting bogged down in things like serving sizes.