code: function serviceUnitsFilterCallback(){
              var arr = _.filter(nutritionList, function(item){
                  return item.fields.nf_serving_size_unit && item.fields.nf_serving_size_unit.toLowerCase();
              });
  
              arr = _.uniq(arr, function(item){ return item.fields.nf_serving_size_unit;});
  
              return $q.resolve(arr);
          }
docs: service units filter