The idea of Food Calories is to make people see what it takes to balance the food that they eat compared with the physical activity they have and motivate them to be more active during the day. Food Calories will show you how much food you can eat depending on the steps you take on the day.
Use it only for reference: Food Calories utilize HealthKit to read your steps data, the total pieces of each food considered are calculated using average food calories and on average people. It may not be 100% accurate, but it will give you a good estimate. We are considering that you burn 0.04 calories for each step you take.