This is why you don't underestimate how much a given amount of food actually is. A kilo could easily fit into your stomach but your gullet can only take so much and if the food's too solid it will have trouble staying down.
One litre of water? Easily downed in a couple minutes.
One kilo of, say, fruit? Should be doable.
A kilo of red meat? Better have fasted for a day and prepare your jaw muscles for the workout of a lifetime. And that's before considering the extra liquid you might need to help swallow it all down.