Blood-sugar test gives us the first way to quantify exactly how hungry you are.

Nature reports on experiments mapping out exactly how hungry people will feel over the next 24 hours – giving a hard number to what’s usually a vague sensation – by measuring how much a person’s blood-sugar level dips a couple hours after breakfast:

Ana Valdes at the University of Nottingham, UK, and her colleagues followed the eating habits of 1,070 healthy adults in the United Kingdom and United States for 2 weeks. Study participants ate a set breakfast and then fasted for 3 hours, after which they ate as they chose. They wore sensors that continuously monitored their blood sugar levels and activity, and logged their meals and hunger levels in a mobile phone app.

Across the group, the drop in blood sugar levels 2–3 hours after breakfast corresponded with the size of the meals that participants ate over the next 24 hours, and matched their reported hunger levels. The authors say that the study, the largest of its kind, provides the best evidence yet that blood-sugar dips could be a possible biomarker for appetite.