How many teaspoons of sugar in milk?

The sugar in milk is lactose, which digestion splits into glucose and galactose. Galactose is converted to glucose mainly in the liver, more slowly. Table 1 of the 2016 paper by Unwin, Haslam and Livesey gives full-fat milk a glycaemic index of 46, in the low band.

The portion is a large 250ml glass. Table 1 lists 12g of available carbohydrate in that glass and a glycaemic load of 5. Worked through without rounding, 12g at GI 46 is a load of 5.52, which gives the published teaspoon figure.

Milk also appears on the chart titled “A healthy breakfast: cereals, toast, fruit juice?”, as 125ml poured over a bowl of bran flakes, with a figure of 1. That is half the glass in Table 1, and consistent with it after rounding.

The Table 1 row is labelled “Milk, full-fat”. Skimmed and semi-skimmed milk have the fat removed rather than the lactose, so they contain a similar amount of sugar per glass. The sugar burden chart gives skimmed milk per 100ml, but its drink figures do not agree with the other charts and none of them is used here; the sources page explains why.

Flavoured milks, milkshakes and sweetened plant milks are different drinks with sugar added. Unsweetened plant milks vary widely too: oat milk contains sugars produced from the oats’ starch during processing, while almond milk contains very little carbohydrate.

Milk’s fat and protein are not part of a glycaemic load.