.... and a data puzzle
You have to consider Biofules to if you look at the like between energy and commodities. Soybeans/ Soybean Oil should be the best example for this connection.
Interesting analysis attempt. You might consider a "farm to fork" market by market structure, however. Probably give you a more comprehensive solution and insight.
In bioinformatics I'm used to papers coming with code, so it's odd that you can't just rerun the same function on the same data. That may have been the results of a hard push for that kind of thing, by Keith Baggerly and others. Keith Baggerly used to describe himself as doing "forensic bioinformatics", and what you're describing here sounds like forensic macroeconomics. I wish more data analysis would take more of a software development approach: your analysis is on github, anyone can clone the repo and run a command to generate the same plots.
Fascinating. In terms of a mass political response it will be interesting to see whether governments in the global South cut fuel and food subsidies like they tried in 2008 and 2010. But with the IMF and Bank saying that they should spend their way out of a crisis it seems unlikely they will do that at least in the short term. We studied the longer-term effects of the 2008-2010 food price rises and it was pretty grim for many years as prices stayed high and wages took a long time to 'adjust' and often only did so when workers had taken to the streets repeatedly or even replaced their governments. A different political moment globally now, with endless magic money trees etc. And utterly different from 1973-74 when so many countries like Bangladesh were barely post-colonial and had very little capacity to cope with global food price shocks.
You mention that the food index is deflated by the US GDP deflator. So, if I understand, I think this means the real cost of food in the US is reaching the cost Americans were paying in the 1970s. But Americans are much richer now, so that is OK, they still have plenty of extra to spend on other things. But you're worried about poor countries I think. So wouldn't there need to be a PPP adjustment too?