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Using data from the Nurses' Health Study II, Bao and colleagues found a higher prevalence of gestational diabetes mellitus (GDM) with increasing potato consumption. 1 The authors stated that the high glycaemic index of potatoes, which causes a sharp postprandial rise in blood glucose concentrations and a risk of associated pancreatic β cells exhaustion, could explain this association.
However, use of the glycaemic index has methodological limitations. Dodd and colleagues found that the glycaemic index of a meal is overestimated by 22-50% when a formula is used rather than direct measurement. 2 This overestimation was unpredictable and food dependent-for example, it was greater for spaghetti than for potato. Glycaemic index therefore has low reproducibility, because potatoes are almost always consumed during meals.
It is not clear how Bao and colleagues calculated glycaemic index and glycaemic load-there is no information in the method section. 1 It is also not clear why they chose potatoes to test this glycaemic...