Its not really clear what the graph is trying to show.
Food being farther right along the x-axis is not inherently better unless weight is a concern. Maybe if you’re hiking or going to space or something, you would want to bring as much protein as possible with minimal weight.
What the graph really says is that legumes have a very low water content relative to other foods like meat. If you dry meat to make jerky, it would be off the chart to the right, around 60% of the total mass being protein.
The y-axis, cost per gram of protein, is interesting on its own. Plotting it against some other variable could maybe show some relationship between $/g and that other variable…
… but this graph doesn’t show much relationship at all, other than “similar foods will land in similar areas on the graph.”
