How many teaspoons of sugar in a slice of brown bread?

Brown bread is the example Dr Unwin and his co-authors chose to explain their whole method. Box 2 of the 2016 paper takes a single 30g slice through each step: how much carbohydrate it holds, how strongly that carbohydrate raises blood glucose, and how the result compares with a teaspoon of table sugar.

The paper starts from 40g of carbohydrate per 100g of bread, which gives 12g in the slice. It takes a glycaemic index of 74 from the international GI tables, which gives a load of 8.88, rounded in the paper to 9. The bread chart prints the same load of 9.

Several charts in the series show this bread, and they do not all print the same figure. The bread chart gives 3.3 for one slice, the value used here. The common foods chart labels its row “Wholemeal, small slice” and gives 3.0 at the same GI. The breakfast chart, which totals a bowl of bran flakes, milk, a slice of toast and a glass of apple juice, rounds one slice of brown toast to 3. “White, brown or green foods?” shows two slices, 60g, at 6. The sugar burden chart lists brown bread in its column of foods digested down into sugars, per 100g rather than per slice.

“Brown” is not a fixed term. In the UK it can mean a wholemeal loaf or a loaf made partly with wholemeal flour. The white, brown or green chart states that its brown bread is wholemeal. In the United States the nearest label is usually whole wheat. The names on the loaf are covered in why brown bread is still sugar.