I think people feel hunger very differently.

When I want to lose wait I just stop eating lunch until I start to feel it makes me sluggish. I can tell I should probably eat but that’s an easy to ignore signal.

My ex girlfriend felt hunger as an all consuming normal activity ending feeling.

Women react differently to things like intermittent fasting given the vastly different hormonal profile to men. I’m much like your ex (I can’t think properly until I feel full, which means a significant breakfast) and anecdotally I have noticed that men seem more likely to go for longer fasting periods. Women’s bodies really don’t like to think they’re starving.