How much sugar did you eat today?

What the number on each food means

Every food in the calculator carries one figure: the number of 4g teaspoons of table sugar that would raise blood glucose by about the same amount as that portion of the food. A slice of bread, a bowl of cereal and a glass of juice are turned into the same unit, so they can be added together and set side by side.

The figure is not the sugar line on a nutrition label. A label counts "sugars" as a chemical group: glucose, fructose, sucrose, lactose and a few others. Starch, the main carbohydrate in rice, bread, potatoes and pasta, is not counted as sugar on a label, yet digestion breaks it down into glucose. The teaspoon figure describes the blood glucose effect of all the digestible carbohydrate in a portion, whatever form it arrives in.

How the figure is calculated

Two measurements describe how a food affects blood glucose. The glycaemic index, or GI, ranks how strongly the carbohydrate in a food raises blood glucose compared with the same amount of pure glucose. The glycaemic load, or GL, multiplies that index by the grams of available carbohydrate in a real portion and divides by 100. GL is the figure that takes portion size into account.

Dr Unwin and his co-authors, Dr David Haslam and Dr Geoffrey Livesey, asked the same question of a teaspoon of table sugar. A 4g teaspoon of sucrose yields 4.2g of carbohydrate once digested, and table sugar has a GI of 65. Its glycaemic load is 4.2 × 65 ÷ 100 = 2.73. Dividing any food's glycaemic load by 2.73 gives the number of teaspoons shown here.

Basmati rice, 150g boiled: 40g carbohydrate × GI 69 ÷ 100 = GL 27.6
27.6 ÷ 2.73 = 10.1 teaspoons

The full arithmetic, with more examples, is on the page what is glycaemic load.

How to read your total

The total is a sum of estimates. Each portion is counted as if it were eaten on its own, and the results are added. That makes the total useful for comparing one day's food with another, one breakfast with another, or one portion size with a larger one. It is not a prediction of the number on a glucose meter.

The line under the total places two figures next to each other: the approximate amount of glucose circulating in an adult's blood at any one moment, and the teaspoon figure for the foods you added. Where the first figure comes from is explained in how much sugar is in your blood.

Portions matter more than names. The cards state the portion each value belongs to, with a gram weight. Two portions of rice are twice the figure for one. If your bowl was about half the stated portion, the figure is about half.

What the method leaves out

• GI values are averages from testing small groups of people, often around ten. Individual responses vary, and sometimes vary widely.
• Cooking time, ripeness, processing and cooling all change GI. Firm pasta and soft pasta, or a green banana and a spotted one, give different results.
• Fat, protein and fibre eaten in the same meal tend to slow and lower the glucose response. The calculator adds each food as if it were eaten alone.
• The values come from UK posters and international tables. Branded products such as breakfast cereals can have different recipes in different countries.
• Glycaemic load describes blood glucose and nothing else. It says nothing about protein, fibre, vitamins, minerals or anything else a food contains.
• A few values are for 100g or 100ml because that is how the source published them. The portion is printed on every card.

Where the foods come from

Of the 69 foods in the calculator, 59 are read directly from Dr Unwin's infographics, 7 come from Table 1 of the 2016 paper, and 3 (meat and fish) are calculated from a carbohydrate content of zero. No value has been estimated to fill a gap. Foods without a published figure were left out, and where two posters give different figures for the same food, both figures are recorded.

Every value, its source and its derivation are listed on the sources page. If you find an error, the contact page explains what to send.