Do zero onset syllables in English start with a glottal stop?

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My Arabic professor was explaining how there are no zero-onset syllables in Arabic because if they don't start with another consonant, they at least start with a glottal stop. He said we do the same thing in English -words like 'Alison' and 'Ian' and 'outside, etc. all start with a glott stop, but we aren't trained to hear it. Is this true?