| Summary: | <h4>Background</h4> <p>Critics of Free Trade Agreements (FTAs) have argued that they threaten public health as they eliminate barriers to trade in harmful products, such as sugar. Here we analyse the North American Free Trade Agreement (NAFTA), testing the hypothesis that lowering tariffs on food and beverage syrups containing High Fructose Corn Syrup (HFCS), an especially harmful type of sugar, increased its use in foods consumed in Canada.</p> <h4>Methods</h4> <p>We used supply data from the United Nations Food and Agricultural Organisation to assess changes in supply of caloric sweeteners including HFCS after NAFTA. We estimate the impact of NAFTA on supply of HFCS in Canada using an innovative quasi-experimental methodology, synthetic control methods, which creates a control group with which to compare Canada’s outcomes. Additional robustness tests were performed for sample, control groups and model specification.</p> <h4>Results</h4> <p>Tariff reductions in NAFTA coincided with a 41.6 (95% CI: 25.1 to 58.2) kilocalorie per capita per day increase in the supply of caloric sweeteners including HFCS. This change was not observed in the control groups, including Australia and the UK, as well as a composite control of 16 countries. Results were robust to placebo tests and additional sensitivity analyses.</p> <h4>Interpretation</h4> <p>NAFTA was strongly associated with a marked rise in HFCS in Canada. Our study provides evidence that even a seemingly modest change to product tariffs in FTAs can substantially alter population-wide dietary behaviour and exposure to risk-factors.</p>
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