Onyayo,
You can either make the existing association Many to Many or you can create 3 separate associations, one for each category that must be selected. If you decide to use a Many to Many association, you'll need to create a microflow and/or some Xpath constraints to ensure that you get one item from each category. With 3 separate associations, you can easily restrict the selectable objects for each so that you get one of each type of food item.
Mike