What the Fibre Index measures

The Fibre Index scores any food on a single question: how much dietary fibre does it deliver relative to its calorie cost?

Fibre is, in our view, the most underrated number on any nutrition label. It is consistently underpresent in convenient and processed food options, rarely mentioned in mainstream nutrition advice with the emphasis it deserves, and yet it is one of the variables most reliably linked to the outcomes people actually care about — feeling full, managing blood sugar, maintaining digestive health, and sustaining energy without crashes.

The index scores on a 0 to 100 scale. The practical ceiling is set at 10 g of fibre per 100 kcal — the upper range of genuinely fibre-dense whole foods. Supplement-grade fibre products like psyllium husk can technically exceed this but are outside the scope of an index designed for evaluating food. In practice, the highest-scoring everyday foods are most vegetables and certain legumes, which is both accurate and worth knowing.

What fibre actually does

There are three mechanisms through which fibre earns its place as the most underrated number on the label.

First, it slows digestion. Fibre forms a gel-like substance in the gut that physically slows the rate at which food moves through the digestive system. This delays the absorption of glucose into the bloodstream, which flattens the blood sugar curve that drives the spike-and-crash energy cycle most people experience after a carbohydrate-heavy meal.

Second, it prolongs fullness. Because fibre slows gastric emptying — the rate at which the stomach empties into the small intestine — a high-fibre meal extends the feeling of satiety beyond what the calorie content alone would predict. A 400-calorie meal with 10 g of fibre keeps you fuller for longer than a 400-calorie meal with 1 g of fibre, regardless of what the macros otherwise look like.

Third, it feeds the gut microbiome. Dietary fibre is the primary food source for the bacteria in the large intestine. A diverse, well-fed microbiome is increasingly linked to everything from immune function to mood regulation to metabolic health. This is a rapidly developing area of research and the full picture is not yet complete — but the direction of evidence is consistent and clear enough to warrant taking fibre seriously as a variable.

How to read your score

The scale uses a logarithmic curve. This means the difference between a food with 0.5 g of fibre per 100 kcal and one with 2 g is shown as larger than the difference between a food with 7 g and one with 9 g — because in nutritional terms, that is accurate. Getting any meaningful amount of fibre into a meal that currently has almost none is a significant improvement. Going from a lot of fibre to slightly more is a marginal one. The curve reflects that reality.

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

A zero note appears when a food contains no fibre at all. This note distinguishes between foods that are naturally fibre-free — protein and fat sources like meat, fish, eggs, and dairy — and packaged grain or snack products where the absence of fibre is more worth examining.

A low note appears when a food scores below approximately 40, corresponding to around 1.5 g of fibre per 100 kcal. This is not a verdict — many whole foods fall below this threshold — but it is a prompt to consider whether this food is the right choice if fibre is something you are trying to increase.

A high note appears when a food scores above approximately 80, corresponding to around 5 g of fibre per 100 kcal. This is a positive signal — foods that reach this level are genuinely earning their calorie cost through fibre density in a way most packaged products do not come close to matching.

The zero score distinction

The most important nuance in this index is that a score of zero means two very different things depending on what the food is.

Chicken breast scores zero. So does a heavily processed snack cracker. Both contain no fibre. But the chicken breast is not a poor food — it scores around 94 on the Protein Index and its fibre score of zero simply reflects that animal protein sources do not contain fibre by nature. The cracker, on the other hand, is made from grain — a source that in its whole, unprocessed form would contain meaningful fibre — and the processing has removed it. The zero note in the calculator addresses this distinction directly, without prescribing a verdict either way.

Reference points

These are approximate scores for common foods:

Chia seeds — 100
Broccoli — 90
Lentils, cooked — 77
Black beans, cooked — 74
Oats, plain — 60
Wholegrain bread — 55
Almonds — 47
Apple — 44
White bread — 26
White rice, cooked — 5
Chicken breast — 0
Eggs — 0
Cheddar cheese — 0

How to use this in practice

In label mode, enter dietary fibre in grams and calories in kcal as they appear on your label. The weight field is optional and for reference only.

In quick mode, enter fibre per 100 kcal directly. The ceiling is 10 g — entering values above this will be capped at 100.

The Fibre Index is most powerful when read alongside the Sugar Index. A food that is high in sugar and low in fibre has nothing to slow the absorption of that sugar — the blood sugar impact is direct and unmoderated. A food that is high in sugar but also meaningfully high in fibre — a whole fruit, for example — has a built-in buffer. The Sugar Buffer Index, currently in development, will combine these two variables into a single score that reflects this relationship directly.

What comes next

The Sugar Index — the fourth of the five base indexes — inverts the scoring direction. Lower sugar scores higher. It uses a sigmoid curve rather than a logarithmic one, designed to be generous at the low end of the sugar spectrum — where differences between naturally occurring sugars in whole foods are minor — and increasingly aggressive as sugar content rises into the range dominated by added sugars in processed products.