It's possible to fit many calories in the stomach over the day with unhealthy, energy dense food. For example oils can have 800kcal/100g, that's why deep fried food contains so many calories. Or if fatties snack 100g of roasted peanuts that would be another 620kcal. And they probably don't even notice the 400kcal from the 1L of coke they drink.  These things are all no problems in a balanced diet of course. But that's probably nothing fatties care about.