Currently, labels tally up to four calories for each gram of carbs and every gram of protein in food. Instead, based on a 2001 study of energy that’s actually available from each nutrient, it’s suggested to count
3.8 calories per gram of sugar
3.6 calories per gram of complex carbohydrates (including starches)
3.2 calories per gram of protein
Multiply the grams of each macronutrient by the numbers above and add to get a more accurate calorie total.
The difference could tally around 10-15 per cent of total calories, 200-300 calories a day and over 1,000 calories in a week for an average person.