To let S Health help you more accurate, you need to add eaten foods during the day to measure your calories intake. To add food in S Health on Galaxy S4 do as follows:
1. Open "S Health"
2. Tap the icon on top left and then select "Food Tracker"
3. Tap the Meal you would like to add: Breakfast, Lunch, Dinner, Other
4. Set the time and date of taken meal
5. Tap the plus icon to add food information
6. Now, you can either search food, or add a customs food (Tap the Star icon to set it as favorite)
7. Specify the amount of the food you've already had by tapping the Dish icon: Extra Small, Small, Medium, Large, Extra Large
8. You can also set the food picture from Gallery or by taking picture with Camera
9. Tap Done on the top right to confirm the process