What the Sugar Index measures

The Sugar Index scores any food on a single question: how much sugar does it contain relative to its calorie cost?

Unlike the Protein and Fibre indexes — where higher is better — the Sugar Index is inverted. Lower sugar scores higher. A food with no sugar scores 100. A pure sugar product scores 0.

The index scores on a 0 to 100 scale using a sigmoid curve — an S-shaped function specifically chosen because sugar behaves differently at different points on the spectrum. At the low end, small differences between naturally low-sugar foods are nutritionally minor and the curve treats them as nearly identical. At the high end, the curve becomes steep — the difference between a moderately sugary product and a heavily sugary one is more significant and the scores reflect that. The steepest part of the curve sits around 10 g of sugar per 100 kcal — the approximate boundary between naturally occurring sugar in whole foods and added sugar in processed products.

An important boundary: this index measures sugar content, not blood sugar impact

This distinction is worth stating clearly because it is the most common source of confusion when people first encounter this index.

White rice scores 100. That surprises most people, because white rice has a well-known reputation for blood sugar impact. The explanation is straightforward: white rice contains negligible sugar. Its glycaemic effect comes from rapid starch digestion — a different mechanism entirely. The Sugar Index measures declared sugar on the nutrition label. Starch is not sugar. The two are metabolically related but analytically separate, and this index is an analytical tool.

Blood sugar impact is a function of multiple interacting variables — sugar content, fibre content, protein content, fat content, the specific type of starch present, and how the food was cooked. No single index captures all of that. The Sugar Buffer Index, currently in development, will combine sugar and fibre into a composite score that partially addresses this — but even that will be a simplified model of a complex physiological process.

For now, use the Sugar Index for what it does well: telling you how much sugar is in a food relative to its calorie cost, in a way that distinguishes between the trivial differences among low-sugar whole foods and the significant differences between genuinely low-sugar and high-sugar products.

What this means in practice: a food scoring 50 is not half as good as a food scoring 100. It means the food is delivering protein at a rate that sits well below the best available whole food sources. A jump from 30 to 60 on this index represents a more meaningful nutritional improvement than a jump from 70 to 90.

The Natural Food / Packaged Product toggle

The toggle at the top of the calculator does not change the score. It changes how the score is interpreted.

A mango scoring 40 on the Sugar Index and a flavoured cereal bar scoring 40 are carrying the same amount of sugar per 100 kcal. But the mango’s sugar arrived with fibre, micronutrients, and water content. The cereal bar’s sugar was added during manufacturing, and it arrives without those moderating factors. The score is the same. The context is not.

The Natural Food setting frames notes around the reality of whole food nutrition — where moderate or even high sugar scores are often contextually reasonable. The Packaged Product setting frames notes around the reality of manufactured food — where sugar scores in the moderate or poor range are more worth examining, and where the ingredient list becomes the next relevant check.

Set the toggle before you enter your values. It takes two seconds and it makes the result more useful.

How to read your score

Three notes are built into the calculator, each triggered at a different point on the sigmoid curve:

An excellent note appears above a score of 75, corresponding to roughly below 8 g of sugar per 100 kcal. This is the range where most naturally low-sugar whole foods and well-formulated packaged products live. The note is positive and brief — a confirmation that sugar is not a concern at this level for this food.

A moderate note appears between scores of 35 and 54, corresponding to roughly 10–13 g of sugar per 100 kcal. This is where the sigmoid curve is steepest — the zone of greatest sensitivity. For packaged products, this is where checking the ingredient list for added sugars becomes most useful. For natural foods, it is simply an observation about sugar content with no particular verdict attached.

A poor note appears below a score of 25, corresponding to roughly above 15 g of sugar per 100 kcal. This is the range dominated by sweetened beverages, confectionery, and heavily processed sweet products. For natural foods reaching this range — fruit juice being the most common example — the note explains why a whole food can score poorly here without being a nutritionally worthless choice.

Reference points

Chicken breast — 100
Eggs — 100
White rice, cooked — 100
Cheddar cheese — 100
Almonds — 97
Plain oats — 98
Broccoli — 97
Wholegrain bread — 96
Plain full fat yoghurt — 88
Whole apple — 73
Flavoured oats packet — 50
Commercial granola — 34
Cola — 5
Fruit juice — 2
Pure sugar — 0

How to use this in practice

Set the Natural Food or Packaged Product toggle first. Then enter sugar in grams and calories in kcal from the nutrition label in label mode, or enter sugar per 100 kcal directly in quick mode.

The Sugar Index is most powerful when read alongside the Fibre Index. A food that scores poorly on sugar but well on fibre — a whole fruit, for instance — has a built-in moderating factor that the sugar score alone does not capture. A food that scores poorly on both has no such moderation. The Sugar Buffer Index, in development, will eventually combine these two dimensions into a single composite score.

What comes next

The Volume Index — the fifth and final base index — measures caloric density: how many calories a food contains per 100 grams. Lower caloric density scores higher. It is the index that most directly answers the question: how much can I eat within my calorie budget? Used alongside the Protein and Fibre indexes, it completes the picture of what makes a food genuinely satisfying relative to its calorie cost.