Loop through fields from 'single'
I think there's a few ways you can do this with twig.

You should be able to check whether the category slug exists as an attribute on the entry object:

{% for category in craft.categories.group('foodMenuCategories') %}
    {% if category.slug in entry.getAttributes|keys %} 
        ...


Or by using the category slug in an array accessor:

{% for category in craft.categories.group('foodMenuCategories') %}
    {% if entry[category.slug] is defined %}
       ...


Or whether the getAttribute() method on the entry model returns anything truthy for that handle:

{% for category in craft.categories.group('foodMenuCategories') %}
    {% if entry.getAttribute(category.slug) %} 
        ...


It's also important, that the slug is the same in every language!