By definition, that wouldn’t be a deficit. You could have a “predicted” calorie deficit that ends up being off by some percentage. The models for energy expenditure typically just use pretty simple demographic info like BMI, sex, age, and activity level. If someone burned less calories than predicted, that basically means that they are less fit than the average person of their demographic cohort.
You could use more advanced models with more information, but they would still be predictions. Drugs also come into play: uppers like caffeine, nicotine, amphetamines, etc, increase the amount of activity in your body so you are literally warmer from burning more calories, everything else equal.
By definition, that wouldn’t be a deficit. You could have a “predicted” calorie deficit that ends up being off by some percentage. The models for energy expenditure typically just use pretty simple demographic info like BMI, sex, age, and activity level. If someone burned less calories than predicted, that basically means that they are less fit than the average person of their demographic cohort.
You could use more advanced models with more information, but they would still be predictions. Drugs also come into play: uppers like caffeine, nicotine, amphetamines, etc, increase the amount of activity in your body so you are literally warmer from burning more calories, everything else equal.