Helper not rerun when property changes

I'm trying to have a helper output nutrient totals based on a list (array) of ingredients. Since I want to display the totals of one of many nutrients I need to somehow pass it a parameter that defines the nutrient in question. So I figured a helper would be the way to go, something like this:

The problem is that the helper is only rendered/run once. However, the helper is updated when a new item is pushed to the list so it seems to be possible. I think I am missing something here. Should helpers be run again if a parameter changes, or should I be trying something else?

The list looks like this:

{
  ingredient: {
    name: 'Potato',
    group: 'Veggies',
    nutrients: [{
      name: 'kcal',
      nutritionalValue: 87
    }, {
      name: 'kJ',
      nutritionalValue: 42
    }]
  },
  weight: 42
}

Here's the Twiddle

Thanks,

Martien