Hunger tends to build gradually and can be satisfied by many foods. A craving is a strong pull toward one specific food (Weingarten 1990), often set off by a cue such as the sight or smell of the food (Boswell 2016). They are different signals with different mechanics, and they may respond to different things.
One trigger researchers have studied is the dip in glucose a couple of hours after a meal. In a study of 1,070 healthy adults wearing glucose monitors, a bigger dip 2 to 3 hours after a meal went with more hunger and eating more at the next meal (Wyatt 2021). The effects were modest, the study looked at hunger rather than cravings, and not everyone dips. Small older studies found that short falls in glucose often came just before people reported hunger (Campfield 1996), and the 2021 study found dip size predicted hunger better than the peak did. How the body registers this is not fully understood.
Another trigger is habit and cues: the 16:00 desk snack, the after-dinner couch sweet. Across 45 published reports, reacting strongly to food cues and reporting cravings predicted eating and weight gain, a moderate link (Boswell 2016). Stress sits on top of both. In a lab study, women whose cortisol rose most under stress ate more afterwards than women whose cortisol rose less (Epel 2001), but stress affects appetite differently from person to person.
IQFood draws an estimated cravings-pressure curve from what you log and your daily check-ins. It is a model, not a measurement, and it changes the question from “why am I weak?” to “which trigger might that have been?”. Changing the routine or the cue may help with habit-driven cravings; stress-driven ones may ease when the stress does.
This is not willpower advice. Cravings are easier to handle when you can see which road you might be on. If cravings or eating feel out of control, or you are preoccupied with food, a doctor or dietitian can help.