Assuming you are right here, which macronutrient (out of protein, fats and carbs) either: a) converts into ATP with significantly less or more than 40% efficiency; or b) is not absorbed in significant fractions by the human digestive system?
I'm not a nutritionist but I'll back up my assertion of 'very little correlation' by drawing attention to the following which aren't taken into account by the calorific value:
- Glycemic Index: how quickly blood sugar levels spike after eating
- Proportional mix of the protein, fat and carbs that you mention (Maybe someone can help me out with a citation on the affect on health, both long and short term, of the different mixes of these).
- Micro-nutritional content: presence or absence of vitamins & minerals
- Poorly understood factors such as whether a requirement to chew (or suck) food prior to swallowing primes the digestive system and/or alters perception of 'fullness' (peanut butter vs. peanuts, sugar in a glass of coke vs. same amount of sugar in hard boiled sweets)
It's also important to remember that foods are not simply energy, but have direct effects on the levels of various neurotransmitters in the brain, leading to feedback loops (sugar addiction comes to mind).
I think you are better off to literally trust your gut over a calorific value.
Otherwise, bah to very little correlation.