multiple fields_for on has_many relationship?

I have a form for an ordered_special. An ordered_special has many
ordered_special_foods. Basically, within a loop in the form I am doing
something like the following:

<% special.foods.each do |food| -%>
    <% fields_for do |os| %>
        <% food.food_types.each do |food_type| -%>
            <div><%= os.radio_button :food_type, %> <%= %></div>
        <% end -%>
    <% end -%>
<% end -%>

So, I am trying to add OrderedSpecialFoods to the OrderedSpecial. The
problem is that I want the radio button to distinguish that we are
handling a different OrderedSpecialFood for each occurrence of the outer
loop. Right now, all of the radio buttons belong to the same group. I
understand why that is, but I want to distinguish between multiple new
OrderedSpecialFoods and I am not sure how to do that exactly. Any help
is appreciated.