'吃饭'， (eat rice= having meal) is a compound word verb, and it is also an intransitive verb (verb that doesn't take object). To illustrate the difference between [single character verb + noun] and [two characters verb + noun], I would change the example to '吃水饺' (吃 + 水饺)
[(吃水饺)- (吃得)- 很快]
[(保守机密) -(保守得)- 很嚴]
As you can see, you can modify '保守' with '得' the same way as '吃'
Although "保守机密保守得很嚴" is technically correct in grammar, it is too wordy. Native speakers would do the following instead
- Shorten a compound word verb to a single character, in the case of '保守', the shortened form is '守'. Your sentence would become "守机密守得很嚴"
In many cases, the object noun can also be shortened -->"守密守得很嚴"
- Only repeat the first character of the compound word verb. For example: "攻击敵方陣地攻击很如火如荼" --> "攻击敵方陣地攻很如火如荼" (omit 击)
The best way is to use a simpler structure [(adv) + (verb) + (noun)] --> [(如火如荼地)(攻击)(敵方陣地)]
- For Intransitive Verbs (verb that cannot take noun), don't repeat the verb after 得 and directly go to the adverb
Example: 战斗 (to battle) is an 'intransitive verb'
Simply write "战斗得很激烈"
"战斗战斗得很激烈" . "战斗战得很激烈" or "战斗斗得很激烈" are all wrong
Another example: '伤风' (get a cold) is an 'intransitive verb'
Simply write "伤风得很严重"
"伤风伤风伤得很严重" or "伤风伤得很严重" is wrong