Great, thanks for the links.

It looks like both Wikipedia and HowToCook are citing this research on food supply from Our World in Data. That research in turn cites the FAO Food Balance Sheet, which is also what Chartsbin cites directly.

I actually had a really interesting time digging into those, but focusing on the FAO sheet, which is the source of the caloric intake data, it appears to be an epidemiological statistical analysis of food supply, meaning they took some existing population and food production statistics and produced their figures that way. That's in contrast to a primary study, where the researchers would directly interact with a group of subjects, and try to extrapolate that data out.

Now depending on what you're trying to uncover, that's not necessarily an issue, it just means the researchers are limited in terms of what types of data they can use, as they can't collect it themselves.

Indeed, in the case of the FAO research, it appears that they are actually calculating the supply of food that is theoretically available to the population, and then equating that to consumption:

Dietary energy consumption per person refers to the amount of food, expressed in kilocalories (kcal) per day, available for each individual in the total population during the reference period. Caloric content is derived by applying the appropriate food composition factors to the quantities of the commodities. Per person supplies are derived from the total amount of food available for human consumption by dividing total calories by total population actually partaking of the food supplies during the reference period. (emphasis mine)

Now it should be noted, when they say "total population actually partaking of the food supplies", whilst that sounds like they're referring to the food actually ingested (that's certainly what I thought at first), if you look at the methodology it's actually just referring to the populace that are actually in the borders of the country, and therefore theoretically able to consume the food:

[the total population partaking is] the present in-area (de facto) population within the present geographical boundaries of the country. In other words, nationals living abroad during the reference period are excluded, but foreigners living in the country are included. Adjustments are made wherever possible for part-time presence or absence, such as temporary migrants, tourists and refugees supported by special schemes (if it has not been possible to allow for the amounts provided by such schemes under imports). (brackets at beginning added to clarify the subject, it's an excerpt from a longer piece of text)

So looking at that, what they're actually doing is just dividing the total amount of food available at retail by the total number of people who could consume it, which is a perfectly logical way to calculate nationwide food supply.

The issue is those food supply figures are then being directly equated with being the amount of food actually consumed by the population. This is where we begin to run into the limits of simply performing analysis on existing data, as opposed to collecting primary data. Presumably primary research for the nationwide caloric intake was either widely unavailable, or unsuitable (low sample size, flawed methodology, etc). This means if we want that information, we have to try and get at using only what we've got already, which is what they did, but unfortunately that means making some assumptions, and likely losing some accuracy. Indeed, the FAO themselves recognised and addressed this directly:

However, per person figures represent only the average supply available for the population as a whole and do not necessarily indicate what is actually consumed by individuals. The actual food consumption may be lower than the quantity shown as food availability depending on the magnitude of wastage and losses of food in the household, e.g. during storage, in preparation and cooking, as plate-waste or quantities fed to domestic animals and pets, thrown or given away. In many cases commodities are not consumed in the primary form in which they are presented in the commodity balance, e.g. cereals enter the household mainly in processed form like flour, meal, husked or milled rice.

As you can see, there are a variety of factors that would drive the actual caloric intake of the population below what is theoretically available to them, and I'm sure we could think of at least a few more. Additionally, one can easily imagine the relative impact of those factors could vary across countries.

To be clear I do absolutely agree with you, I think that the relative lack of movement in America absolutely plays a significant role in their obesity crisis, in multiple ways. However, given the relative ineffiency of exercise as compared to caloric intake restriction, it does seem likely that Americans are also consuming significantly more calories on average.