Can we really blame the state of a nation on increased portion sizes? Sure we can. It's not the only factor, but is a large contributor. Have you ever found it hard to resist buying that large size (insert processed food here) because it was only a few cents more than the medium, which in turn was only a little more than the small? Why would you just buy the small - that would be a waste of money.
Unfortunately food sellers know this and a lot of their research goes into pricing models that will extract the most money from us, for the least cost to them. This equates to them finding the cheapest way to provide food in quantity. They are not setting out to try and make you fat. It's just that offering a customer that equates portion size with good value, is good for business.
Consumers who are asked whether they “want fries with that”, to up-size their order, or choose a “Value Meal” instead of going with their original choice, are being manipulated by a psychological effect called the endowment effect. This is where they feel the pain of loss more than the satisfaction of gain (it hurts more to lose something than gain something) – that can lead them to consume more than they actually need.
This effect is similar to the wealth effect, where we adapt our lifestyle to suit our income, rather than simply saving more as we earn more. Ultimately, access to highly processed, energy dense food has meant that we have increased our purchasing and eating behaviour to catch up with its availability, rather than continuing to consume as we have always done.
Next time you're asked to up-size or reach for the large option because it's just a few cents more ask yourself if you are really hungry for that extra quantity, or if you may be just feeling the endowment effect.
New Zealand has followed a similar trend over the years, as have most western cultures.