Count the calories as you eat. It’s a good idea to have an idea of the calories that most food items have. If it is a packed thing then the label is sure to have the calories that the substance has. Divide the KJ by 4.2 and that gives you your calories.
Be sure to burn off any extra calories by the end of the week.
Purchase a get2it food diary available on this website and start tracking your food/calorie intake.