> I'd be starving and unproductive all afternoon. What's the secret?
You'd think that, but it's a tricky thing listening to our bodies: That feeling you associate with hunger can also be triggered by your stomach being empty or being on the far side of a sugar/carb spike.
Real hunger is a very different feeling. I often fast(†) 2-3 days in a row (sometimes as many as 4) and I definitely don't feel real hunger the first two days of not eating (and rarely before day four). It feels awful in a way you're not likely to confuse with the feeling you have midday, but fortunately dealing with an empty stomach is easy: Have some water (or a coffee/tea; decaf is ok). 20 minutes later your stomach has something in it and something to do (more if it's cold water) and you can get on with your day.
The second part is that sugar-spike: That's a killer for me. If you're getting too many of your calories from sugar your body will respond fast to the lack of sugar (even though you've got plenty of calories) and you will feel hungry even if you're not. Everyone who has eaten a candy-bar on an empty stomach has felt this a few hours later, but there's not much you can do except eat less sugar, and get your calories from something less spiky like fat and protein. This is probably the single biggest reason low-carb diets are successful, because you don't get that carb craving feeling.
(†) I usually mean zero-calories by this, but I travel around twenty times a year and it's often really helpful to get some new calories at the right-time-of-day to help adjust to the local timezone, so I might have as much as 600kcal in a day and still consider it "fasting". This is still far less than what many people have in even a single meal, and I'd have no problem with my energy-level or really anything else doing it continuously except for the fact that I really do like to eat.