Why do low-income households eat so much garbage?
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Don't you think you might be getting things backwards? The offer in poor neighborhoods is determined by the demand in those neighborhoods, not the other way around. The shops are selling what the people want to buy.
I've lived in mixed neighborhoods in Europe, where everything is available within walking distance. The poorer people still buy junk food while more wealthy or educated people buy healthier food.
The paper referenced in the x-tweet is "Food Deserts and the Causes of Nutritional Inequality", which can be found eg here[1].