Are food calorie values really integers? According to what I've seen, fat has a listed caloric value of 9 Cal/g, while carbs and protein have listed caloric values of 4 Cal/g.* Are these numbers exact, or have they been rounded? And if they have been rounded what are the exact numbers? One hit said that the numbers are rounded, but not by how much.
*These are &quot;food calories&quot; (aka &quot;large calories&quot; or &quot;Calories&quot; with a capital &quot;C&quot;).
1 food calorie = 1000 &quot;small calories&quot; or &quot;gram calories&quot; = 1 kcal = 4.184 kJ
See: https://en.wikipedia.org/wiki/Calorie
They're not exact numbers. These numbers aren't exact for three reasons:

Each type of carb, protein, and fat has a different caloric value.  These are overall averages for each class.

Even if you were dealing with a single pure compound, the value couldn't be exact because there is individual variation in how much of that compound is metabolized based on digestion, absorption, etc.

Even if #1 and #2 were not issues, the number still couldn't be exact, because it is a measured value, and measured values are never exact.  Only counted numbers, and values that are exact by defintion (e.g., the speed of light) are exact.


To get a better idea of how these values are determined, and the issues and uncertainties associated with measuring them, I'd recommend reading through:
Food and Agriculture Organization of the United Nations. FAO food and nutrition paper. Chapter 3:  Calculation of the energy content of foods - energy conversion factors. Food and Agriculture Organization of the United Nations, 1979.
Here is a direct link to chapter 3:
http://www.fao.org/3/Y5022E/y5022e04.htm