The calorie is a measure of energy. All "calories" have the same energy content. 1 kj = 4.2 calories, and some products will show energy in either cal/kj.
However, this does NOT mean that all calorie sources have the same effects on your weight.
Different foods go through different processes that can have vastly different effects on hunger and the hormones that regulate body weight.
For example, a protein calorie is not the same as a fat calorie or a carb calorie.
Replacing carbs and fat with protein can boost metabolism, reduce appetite and cravings, while optimizing the function of some weight-regulating hormones.
Its important too to consider the GLYCAEMIC INDEX/LOAD different foods have.
High GI foods will spike insulin suddenly, giving you a quick BOOST – but this will be shortly followed by a CRASH – this leads to craving more food – and overeating
Its good to consider a high protein / low GI lifestyle after surgery, as it will have less impact on insulin levels and will prevent insulin resistance. Remember – the body cannot liberate fat for energy in the presence of insulin.
A GI rating below 50 is good for weight loss and maintenance.
Here is a good link to a food GI guide https://www.gisymbol.com/about-glycemic-index/?gclid=EAIaIQobChMIlp-P0Pz02gIV2yMrCh2v1APEEAAYASAAEgIxbPD_BwE