How many teaspoons of sugar in mushrooms?

Mushrooms contain very little of the carbohydrate that raises blood glucose. Table 1 of the 2016 paper by Unwin, Haslam and Livesey lists 0.3g of available carbohydrate in an 80g portion, about a cup of sliced mushrooms. That is the smallest carbohydrate figure in the table.

The table gives mushrooms a glycaemic index of 70. The paper explains that this GI was calculated from the food’s carbohydrate composition rather than measured in volunteers, and that such values are likely to be overestimated. A conventional GI test would hardly be practical: a test portion containing 50g of carbohydrate would weigh many kilograms of mushrooms.

The table prints a glycaemic load of 0.03. Worked from its own inputs, 0.3g at GI 70 divided by 100 is 0.21, and the teaspoon figure in the same row, 0.1, matches 0.21. This site records the calculated load. The mismatch is listed on the sources page, along with similar ones in the cauliflower and tomato rows.

Mushrooms are fungi, not plants, and their cell walls are built from chitin rather than cellulose. Much of their small carbohydrate content is fibre and the sugar alcohol mannitol, which are not counted as available carbohydrate.

The common foods chart names mushrooms, with chicken, oily fish, almonds, cheese and meat, in its note of foods in the very low glycaemic range. Table 1 is the only source that prints a figure.

The figure is for mushrooms on their own. Mushrooms fried in butter or oil take on fat but not carbohydrate; breaded mushrooms are a different food.