A lot of people and research focus on coffee suppressing appetite, which is downstream to the cortisol-raising effects of fight-and-flight response which raise blood sugar among a myriad other things. What they forget is that elevated blood sugar and cortisol eventually results in lower blood sugar than baseline — which is when the hunger strikes.

So yes, coffee is an appetite suppressant, but 6-8 hours later your appetite rebounds. Many people don't feel this effect simply because they have frequent-enough meals and/or coffees to stay ahead of the blood sugar crash. If you get into intermittent fasting, it's pretty easy to notice. In my quest to fix my metabolism, I am constantly aware that my morning cup of coffee is the biggest reasons why I get ravenous around 5pm.