Just an idea, but can shrinkflation on junk food have the side-effect of reduced obesity?

Unlikely. A person who is a junk-food addict is more likely to simply buy two of <whatever food or snack> and eat both of them, as opposed to eating less on account of the portion size.

Addicts are going to get their fix, no matter what.

Probably not, though INFLATION might. When people can’t afford food, they might lose weight.

Might be, since the contentious part of shrinkflation is not just that the amount shrinks, but the price stays the same. It is a defacto price increase. So someone who already eats mostly junk food for cost reasons probably would not be able to afford 2 packages of the same product to compensate.

They’ve already done that. Candy bars, chips, etc contain less product than they did 20 years ago. Same price or increased.

Not unless that is all you eat.