How many teaspoons of sugar in a baked potato?

The baked potato is the worked example in Box 1 of the 2016 paper by Unwin, Haslam and Livesey, their step-by-step explanation of how a glycaemic load is calculated. The paper takes a 150g potato, about one medium baking potato, and asks two questions of it: how much carbohydrate does it contain, and how strongly does that carbohydrate raise blood glucose?

For the first, the paper uses 17g of carbohydrate per 100g, which gives 25.5g in 150g. For the second, it uses a glycaemic index of 86. Multiplied together and divided by 100, that is a glycaemic load the paper rounds to 22. The paper’s Figure 1, its version of the common foods chart, prints 8.2 teaspoons for this potato, and that is the value used here.

Taking the paper’s own numbers to the end gives a slightly different result. The rounded load of 22, divided by the glycaemic load of a teaspoon of sugar, is 8.1; the unrounded load gives 8.0. Neither is 8.2, and the paper does not account for the difference.

A larger disagreement comes from the sugar burden chart, which lists baked potato in its column of foods digested down into sugars at 6.3 teaspoons per 100g. Scaled to 150g, that would be 9.5. Neither source explains the difference, and both figures are recorded on the sources page.

The figure is for the potato alone, as the paper presents it. Butter, cheese, beans and other fillings are separate foods, and fat and protein eaten at the same time tend to slow the glucose response of a meal.

The same kind of potato boiled, with a GI from a different table entry, is on the boiled potato page.