About the garbage food problem... you can blame most of that on the corn subsidies. Most of the US is actually poorly suited for growing corn with many much better alternatives... so the only reason that corn is the biggest cash crop is because of the massive incentives by the government. It started out necessary and just grew pointless and out of control. Only a couple percent of the corn grown in the US is directly used as human food. About 50% goes to animal feed, which is what fuels their unhealthy diet and therefore ours, 40% goes to ethanol, which is just plain stupid to do with a food crop versus cellulose and other inedible forms and is only ever bought because the US gives it a huge tax incentive plus a protection tarrif from sugarcane ethanol, and about 7-8% goes to corn oil, starch, and syrup.
Without the corn subsidies it is more cost effective, and therefore people would do it, to grow GRASS for cattle. It's about ten times more efficient to grow hemp for ethanol WITHOUT the massive pesticides, fertilizer, and irrigation needed for corn (Though much of the reason we don't do this is because the government makes no distinction between it and marijuana.) Remove the corn subsidies and you might find vegetables cheaper than beef for once. It would put real sugar back. Growing organically with lots of variety would be worthwhile for big corporations. And considering that 70% of the amazon rainforest destruction is for growing cattle feed for the US, if growing locally is a cheaper alternative that would basically stop the rainforests annihlation.
/end rant. Now you know a big thing to blame, at least.