Foocat

The science, and its limits

Foocat turns a bag of cat food into two numbers you can act on: how much carbohydrate it contains, and how much protein — both on a dry-matter basis so you can compare foods fairly. This page explains why those numbers are worth your attention, exactly how we work them out, and — just as important — why you should treat them as a well-informed guide rather than a lab certificate.

Why these numbers matter for a cat

Cats are obligate carnivores. Unlike dogs or people, they are built to run on animal protein and fat, not carbohydrate. Cats need roughly two to three times as much dietary protein as a comparable omnivore, they burn protein for energy even when the diet is low in it, and they have very limited machinery for handling large amounts of dietary sugar and starch. So the balance of protein versus carbohydrate in a food is a genuinely meaningful thing to know — and it’s the one thing a cat-food package tends not to spell out.

The authoritative reference for what a complete cat food should contain in Europe is the FEDIAF Nutritional Guidelines, which state nutrient allowances per unit of dry matter and per 1000 kcal. That’s the same reason Foocat converts everything to a dry-matter basis: comparing a wet food (≈80% water) with a dry food (≈10% water) on their “as-fed” percentages is meaningless, because water dilutes every number differently.

A fair caveat in the other direction: carbohydrate is not a poison for cats. The evidence that moderate carbohydrate directly harms an otherwise healthy cat is genuinely mixed — one meta-analysis found dietary carbohydrate did not, on its own, raise body fat or fasting glucose in healthy cats. Think of the carb figure as useful information worth acting on where it’s easy, not as a verdict.

How Foocat calculates the carbs

European pet-food labels list the analytical constituents — protein, fat, fibre, ash (minerals) and moisture — but almost never carbohydrate, because there’s no legal requirement to. So we do what pet-nutrition scientists do, and calculate it by difference: whatever mass isn’t protein, fat, fibre, ash or water is treated as carbohydrate.

carbohydrate ≈ 100 − protein − fat − fibre − moisture − ash

When the label omits fibre or ash, we fill in a typical estimate (about 0.5% for fibre and 7% for ash — a European average) so the carb figure stays realistic. We then express carbohydrate and protein on a dry-matter basis so two foods can be compared side by side.

Why no label number is the whole truth

This is the part every cat-food app should say out loud. The figures on a package — and therefore the figures we read from it — are more approximate than they look:

  • The label states legal minimums and maximums, not actual values. Protein and fat are guaranteed minimums; fibre, moisture and ash are maximums. A food that says “minimum 24% protein” might really contain 32% (Tufts Petfoodology). Because these are bounds rather than one real recipe, the declared values don’t even have to add up to 100% — which is why the calculated carb figure sometimes bottoms out at zero.
  • Independent lab tests find labels are often wrong. One study of 20 commercial cat foods found 9 of them did not match their own guaranteed analysis (Gosper et al., Australian Veterinary Journal, 2016). A separate analysis of 27 Canadian pet foods found only 9 met all of their label claims (Burdett et al., The Canadian Veterinary Journal, 2018).
  • “Carbohydrate by difference” inherits every other error. Because we get carbohydrate by subtracting everything else, any inaccuracy in protein, fat, fibre, ash or moisture flows straight into the carb number, and the calculation also sweeps in things like soluble fibre. Small differences between two foods may not be real (Tufts Petfoodology, “Carb Confusion”).
  • Foocat reads the label with a camera and AI. The values are recognised from a photo of the package by on-device text recognition and an AI model. We guard against obvious mistakes (for example, a value read as 305% is thrown away), but a misread digit can still slip through. Always sanity-check against the package in your hand.
  • These numbers say nothing about quality. The analytical constituents don’t tell you about ingredient quality, digestibility, or whether the protein supplies the amino acids a cat needs (such as taurine). A food can hit every headline percentage and still be a poor choice, or vice versa.

How to get the most out of Foocat

  • Use it to compare foods on the same footing (dry-matter basis), not to chase a single “correct” percentage.
  • Treat the numbers as a starting point. If a figure looks surprising, re-scan in better light, or tap a value in the app to type in what the package actually says.
  • For a health decision, ask the manufacturer for a typical (average) analysis rather than the guaranteed minimums, and talk to your vet — Foocat is an aid to choosing, not a substitute for veterinary advice.

References

  1. FEDIAF. Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs. europeanpetfood.org
  2. Tufts Cummings Veterinary School, Petfoodology. What Is Guaranteed about the Guaranteed Analysis? (2020). Link
  3. Tufts Cummings Veterinary School, Petfoodology. Carb Confusion, Part 2: Measuring and Comparing Carbohydrate in Pet Foods (2021). Link
  4. Gosper EC, Raubenheimer D, Machovsky-Capuska GE, Chaves AV. Discrepancy between the composition of some commercial cat foods and their package labelling and suitability for meeting nutritional requirements. Australian Veterinary Journal, 2016;94(1–2):12–17. PubMed
  5. Burdett S, Mansilla WD, Shoveller AK. Many Canadian dog and cat foods fail to comply with the guaranteed analyses reported on packages. The Canadian Veterinary Journal, 2018;59(11):1181–1186. PMC
  6. Verbrugghe A, Hesta M. Cats and Carbohydrates: The Carnivore Fantasy? Veterinary Sciences, 2017;4(4):55. Link

Foocat is on the App Store for iPhone and iPad, and on Google Play for Android.