The idea that eating healthily can be simplified to the reduction in a single number (a calorific value) really annoys me.
Always remember that a calorie is a proxy metric, and a very poor one at that; it's the energy output of burning the food, which has very little correlation with what goes on in your body during consumption/digestion.
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.
It really annoys me as e.g. the trend in industrial bread making is to reduce the relative quantity of flour (the most expensive ingredient), in favour of cheaper vegetable fats. This is achieved by the addition of emulsifiers. So the calorific value of the bread may go down, and you'll have to eat more bread to make you feel as full, but the overall nutritional balance is completely skewed away from what was originally a quite nourishing, wholesome food (the majority component of the European diet at one time).
Next time you buy a loaf of bread look at the end of the list of ingredients. If there is an emulsifier listed it's a red flag; there really should only be Flour, Water, Yeast and (some) Fat. You can also tell the quality of the bread by squeezing it and feeling for the spring-back. Many supermarkets don't actually stock 'real' bread.
Always remember that a calorie is a proxy metric, and a very poor one at that; it's the energy output of burning the food, which has very little correlation with what goes on in your body during consumption/digestion.