Speaking from my own experience, mental hunger IS hunger. It's the first sign that I need to eat, and then a clear indicator that I need more. That thing where you're constantly thinking about food, wanting to eat, feeling like you need to eat, daydreaming of things you shouldn't eat, questioning whether you can eat, that's hunger. All of it. Who knew? 🤷♀️
Diet culture had me bamboozled into thinking it was some kind of a trick. I never trusted it, but it turns out to be completely legit. If I am not at all hungry, I don't daydream about eating food. It doesn't even occur to me. I have little interest even if food is offered. Having been chronically hungry for like, decades, this was a revelation!
There is a miraculous difference in my overall consumption if I act on that first inkling that I could eat something rather than questioning or ignoring it for several more hours. I used to let myself get really stomach-growling hungry (aka, waaaay too hungry) and then wait another hour after that before I would eat. No! That's nuts. It caused me to eat like a starving animal and never want to stop. Now, I'll be going about my business, think, "Oh, a sandwich sounds good" and I'll just go and make one right then. If it's an hour before dinner, maybe I'll make a half sandwich, or maybe I'll decide to order a big deli sandwich for dinner and have a few bites of something else while I wait for delivery. What I don't do is tell myself that I can't possibly be hungry or that I'm not allowed to eat. I also don't wait until I'm really, really hungry and then try to eat some boring food that I'd previously planned and no longer want. All of that creates a big disconnect. People who ignore hunger also tend to ignore fullness.
What about emotional or habitual eating, numbing out with food? That too is ignoring hunger and fullness. Maybe it's filling an emotional void rather than being a response to restriction, but the answer is the same. You get curious about what you actually need on a mind/body/soul level and then you meet the real need. Maybe it's more food, a hug, a nap, a day off, something to look forward to, or a friend to talk with. If your motivation is to take the best care of your body and mind, then no worries about doing it wrong.
It took me a long time to realize that I don't typically feel stomach-growling hunger. If I'm stressed even the littlest bit, it throws off my hunger signals. So, like you said @skwigg, that mental hunger is my first sign that I'll need to eat soon.
When I first started "intuitive eating", I (like many folks) made the mistake of turning it into the hunger/fullness diet. If I wasn't stomach-growly hungry, I shouldn't eat. But I quickly learned I would eat hardly anything at all if I waited for that feeling.
For me, making sure I'm eating consistently is absolute key. I don't necessarily eat "by the clock" anymore, but I am on a regular schedule with my corporate job, and I do keep an eye on the clock because if 4-5 hours have passed, I probably need to eat. Going more than 5 hours between meals/snacks always, ALWAYS backfires on me. My workouts suffer, energy plummets, mental clarity escapes me, and/or I end up going ape shit on the pantry later that night.
I do chalk my skewed hunger signals up to literal years of disordered eating. I've done a lot of reading on how that can be messed up for a long time, even post-recovery. I know that eating regularly is a form of self-care for me now, tummy rumbling or not.