As other answers stated, 下去 can function as a directional/result word particle for 'down' e.g. 吞下去; It can also function as a verb for 'go down' e.g. 我要下去
But when 下去 is functioning as an adverb for "continue". It must be placed after a verb. e.g. 等下去
I want to say:
我吃下去 = I continue eating.
To avoid confusion, you can write "我(繼續)吃下去" or simply "我繼續吃".
Another way to make "我吃下去 (I continue eating) not ambiguous is to add more context. For example, 我再吃下去也不會喜歡上這東西