I can’t digest pork well (it runs right through me and frequently causes vomiting), so I don’t l eat it, but if I were to follow a diet with 500 calories of pork in it, I might get 100 from it. On the other hand, I digest beans and lentils incredibly well, with no noticeable gas. I can imagine that I might actually get 110 calories from a “100 calorie serving.” It is possible to determine your caloric intake despite this variation, but because people aren’t well educated about it, they see a mismatch in the math and reality and think it’s pointless to calculate it at all instead of realizing they need to adjust it for their specific digestive system.