What is the unstressed vowel in fattening?

The unstressed vowel in "fattening" is the "e" in the first syllable, "fat".

Here's why:

* Stress: The word "fattening" has the stress on the second syllable, "ten".

* Unstressed Vowels: Unstressed vowels often have a reduced sound. In this case, the "e" in "fat" is reduced to a schwa sound (ə).

So, while we spell it "fattening," the pronunciation is closer to "ˈfætənɪŋ".