How exactly are carbohydrates eliminated or reduced in foods (such as pre-packaged frozen meals or snacks)?

Answer 1

One major way in which they are reduced is by not adding them in the first place. Most manufactured foods are laden with sugars, and even things that seem natural may be covered in a sugary or fatty sauce in such packages.

Of course, in some cases actual changes of recipes have occurred. Instead of using sugar or corn syrup, some manufacturers will produce low-carb products with sucralose and sugar alcohols instead (technically carbs, these are indigestible... so they don't count). Likewise, some products have replaced wheat flour with soy flour - that's how you get low-carb pasta (if that's not a contradiction in terms!).

Another large way in which such foods seem to have proliferated is by labelling. Many foods were comparatively low in carbs all along, but they just didn't announce the fact to the world. And of course some labelling is a bit dubious too - it's often better to look at the nutritional information on a package than the words in huge type.

Answer 2

Other things are substituted for the carbs, usually sugar substitutes replace sugar.