A new analysis reveals that Canadians had access to about 170 extra calories per day after the first Canada-U.S. free trade agreement — a caloric boost attributed to an increase in highly processed food that flooded into Canada after U.S. trade barriers were removed.

That increase in available calories was estimated to be enough for some Canadians to gain as much as 27 pounds (12.2 kilograms) and could have contributed to rising obesity in Canada.

That’s the finding of the UK study that looked at the “natural experiment” created when Canada and the U.S. negotiated the original free trade deal in 1989 — a deal that became a prototype for the North American Free Trade Agreement (NAFTA) and other international trade negotiations.