It is completely untrue to say that take-away and junk food are cheap calories, and that people eat them because healthy food is expensive. Do the maths.
Yes, activated organic jimbu salad from a trendy hipster cafe is beyond many families, but there are cheaper options.
Even if you buy coca-cola cans in bulk for the cheapest price around here, you are still paying $A10.00 per kilo for the carbohydrate content. The same supermarkets sell rice for a dollar per kilo, or about SA1.40 per kilo of carbohydrate. And take-away is hugely expensive as a source of protein.
These PNG highlanders lived on not much more than a dollar a day, had very little formal education and didn't speak English, but they knew how to eat healthy. No, they are not cannibals, but they do know how to set up an interesting photo for a gringo.
What little communal money they had was spent on 20 kg sacks of rice and the cheapest fish they could buy - usually boxes of tinned mackerel. They grew/gathered vegetables and occasionally caught small animals and birds in the forest. They never bought take-away or junk food. They couldn't afford it.
Attempts by health groups to supply fresh vegetables to people in remote parts of central Australia are completely misguided, expensive and wasteful when the produce wilts before reaching its destination. Tinned and dried vegetables are extremely nutritious. I know of no research which shows a convincing health benefit of fresh vegetables over an ample supply of preserved ones.
In fact, in his book Guns, Germs and Steel, Jared Diamond theorised that learning to manage without fresh produce contributed to the success of Western civilization. In fact it is really only since the end of WW2 that much of northern Europe has had year-round access to fresh salad vegetables.
Take-away and junk food are industries supported by ignorance, not lack of money.