The same dish served in two countries can arrive in noticeably different quantities. The difference is set by packaging, restaurant economics and tableware rather than by appetite.
Packaging fixes the unit before anyone eats
Most food is bought in containers sized by manufacturers, and a container is frequently treated as one serving regardless of what the label states.
Where a market's standard bottle or packet is larger, the informal unit is larger, and consumption follows the container rather than the stated portion.
Regulations requiring per-serving labelling do not change this, because the physical package remains the thing people actually divide their eating around. A label stating that a bottle contains two and a half servings is read, if at all, as information about the bottle rather than as an instruction.
Restaurant cost structures push in opposite directions
Where labour and rent are the dominant costs and ingredients are comparatively cheap, generous portions are an inexpensive way to signal value.
Where ingredients cost more relative to rent, the same signal is delivered through presentation, courses or quality instead of volume.
Neither approach reflects a view about how much a person should eat. Both are responses to which input a restaurant is trying to economise on.
Refills and side conventions compound the effect
In markets where drink refills are included, the portion is effectively unlimited and the listed size is only the first serving.
Elsewhere each drink is charged separately, which makes the quantity a repeated decision rather than a single one.
Bread, sides and condiments work the same way. Whether they arrive automatically or must be ordered changes the total substantially, and the difference is invisible on a menu that lists only the main dish.
The plate itself grew
Standard dinner plate diameters have increased over the last several decades in many markets, and restaurant plates increased alongside them.
A fixed quantity looks sparse on a larger plate, so kitchens serve more to make the plate read as full.
Because the change happened gradually across an entire supply chain, almost nobody experienced it as a decision to eat more. Manufacturers followed retail demand, retailers followed restaurant fashion, and no single actor chose the outcome.
Familiarity anchors what looks normal
People judge portions against what they grew up seeing, not against any measured quantity.
That anchor is why travellers describe portions elsewhere as excessive or mean, while residents of both places consider their own unremarkable.
It also explains why portion norms shift slowly. The reference point is formed in childhood and is reinforced daily by every meal served around it.