doesn't it rather suggest that parents are less likely to purchase junk food for their kids if the cost exceeds some psychological barrier point? a chocolate bar at $0.99 might seem like it's pocket change, and it's worth it to shut the kid up; but at $1.15, it's no longer affordable.
it's worth asking, though, if that's sort of good enough. i mean, there's a huge difference between parents feeding their kids garbage and consenting adults deciding what to put in their own bodies.
i could type a long response and a short response to this, and i'm going to pick the short response.
a lot of what is being discussed here relates to the idea of placing normative value judgements on a decision-making process that is more complicated than is being let on. at the end of the day, humans need sugar and calories more than they need vitamins and fibre, so when poor people find themselves in a situation where they have limited resources, it actually makes sense for them to choose the diet options that are higher in fuel than the ones that are lower in it. you might not realize that if you take a sort of an elitist perspective on it, which is something this presentation does in multiple places.
if you have $20 and you have to make it last, you really should buy lard, rather than vegetables. that's the correct choice, in context. that's just the simple mathematics of it.
but, it means you need to be relatively active, in order to burn the extra fuel, and i think that's the fundamental error being made here and by a lot of policy experts: they focus on restricting diets, rather than on coercing people to be more active. that's really what they're doing wrong.
i haven't seen studies on the topic, but i'd strongly suspect that if you were to get people to exercise more then a healthier diet would follow as a corollary; you wouldn't need to get people to change their consumption patterns, if you could just get them out and about. they'd do it on their own.
we could have these big debates about consensual behaviour and statist overreach, but in the end i want to push the policies that i think are going to work, and it doesn't seem like any of these attempts to try to restrict people's diets are likely to work. but, if we look at the kinds of jobs we do - from working cash registers to sitting on computers - the commonality is that we spend most of our time at work sitting down, nowadays.
it would actually be relatively simple to legislate a rule enforcing an amount of mandated cardio at work. and, that's the path i'd advocate walking down - not restrictions on diet, but the renormalization and legal mandating of physical activity in the workplace.