How to read a pet food's macronutrient profile: a how-to guide
How to read a pet food's macronutrient: The guaranteed analysis on a pack looks simple and is quietly misleading. Crude protein, crude fat, crude fibre (US: crude fiber), moisture and ash are printed as percentages on an as-fed basis, which means a kibble and a wet food cannot be compared directly: one is nearly dry, the other is mostly water. To compare like with like you convert every figure to a dry-matter basis by dividing the as-fed figure by the dry-matter percentage and multiplying by one hundred (FEDIAF, 2024). Carbohydrate, which is never listed, is then estimated by difference. This guide turns those steps into a repeatable method and walks through a full worked example.
Last updated :General documentary information. For an individual animal, a veterinarian's advice takes precedence over any online content.
The aim is not to replace a veterinarian but to let you read a label honestly: to see past the moisture illusion, to estimate the hidden carbohydrate, and to know where the numbers stop and quality begins. It is informational, and any medical diet remains a matter for professional advice.
On this page (read food)
- Why convert everything to a dry-matter basis?
- How do you do the conversion, step by step?
- How do you estimate the carbohydrate the label hides?
- Why relate protein to the food's energy?
- A fully worked example: kibble against wet food
- Where do the numbers stop and quality begin?
- What common mistakes distort label reading?
- Recommendation: a reliable reading routine
Why convert everything to a dry-matter basis? {#dry-matter}
Answer capsule: Because as-fed figures are diluted by water. Kibble moisture sits around 8 to 10 percent and wet-food moisture around 75 to 82 percent, so comparing them as printed means comparing a near-dry food with one that is three-quarters water (FEDIAF, 2024).
Dry-matter conversion neutralises that water so the nutrient content can be compared fairly. The effect is large and routinely flips intuitions: a wet food that looks poor in protein on the pack can exceed a kibble once both are put on dry matter. The same logic applies to every nutrient, protein, fat and ash alike, and to any comparison across formats.
This single step is non-negotiable for honest comparison. Skipping it is the most common reason owners reach the wrong conclusion about which of two foods is richer.
How do you do the conversion, step by step? {#conversion-steps}
Answer capsule: Dry matter equals 100 minus moisture. The dry-matter figure for any nutrient equals its as-fed figure divided by the dry matter, multiplied by one hundred (FEDIAF, 2024).
In practice the routine is three short steps. First, find dry matter: subtract the stated moisture from 100. Second, for each nutrient you care about, divide its as-fed percentage by the dry-matter percentage. Third, multiply by one hundred to return to a percentage. If moisture is not shown, estimate it at about 8 to 10 percent for kibble and 75 to 82 percent for wet food.
The rule cuts both ways: it makes a wet food look richer and a dry food less extreme than the pack suggested, while the real gap between them narrows. Once you have done it twice it becomes mechanical, and it is the foundation for everything that follows.
How do you estimate the carbohydrate the label hides? {#carbohydrate}
Answer capsule: Carbohydrate is estimated by difference: subtract protein, fat, moisture, ash and crude fibre from 100, the nitrogen-free extract method (FEDIAF, 2024). It is an approximation, but the only practical one.
No regulation requires carbohydrate to be printed, so you reconstruct it from what is. Take 100 and subtract the crude protein, crude fat, moisture, crude ash and crude fibre percentages; the remainder is the nitrogen-free extract, a working estimate of digestible carbohydrate. When ash is not given, it is sometimes estimated at a few percent, which keeps the result an estimate rather than a measured value.
Do the carbohydrate estimate on the same basis as the rest, ideally dry matter, so it can be compared between foods. For a cat in particular, this estimate is the only way to judge a level the pack never states and that a grain-free claim does not reveal.
Why relate protein to the food's energy? {#energy}
Answer capsule: Because a percentage does not account for how much an animal eats. A calorie-dense food is eaten in smaller amounts, so the fine unit of comparison is grams of protein per 1,000 kcal, not the raw percentage (FEDIAF, 2024).
At equal dry matter, the more calorie-dense food delivers less protein per calorie consumed. Two foods showing the same protein percentage can therefore provide different daily protein once energy density is taken into account, and an animal can be short on a richer-looking dense food while covered by a leaner-looking one. Where energy figures are available, converting protein to grams per 1,000 kcal removes this distortion.
This is also why regulatory minimums are indexed to energy: FEDIAF expresses its recommendations relative to metabolisable energy precisely so that a denser food carries a higher percentage minimum.
A fully worked example: kibble against wet food {#worked-example}
Answer capsule: A wet food at 10 percent protein and 80 percent moisture reaches 50 percent protein on dry matter, against about 32.6 percent for a kibble at 30 percent and 92 percent dry matter. The ranking flips after conversion.
Take the wet food first. Moisture is 80 percent, so dry matter is 100 minus 80, that is 20 percent. The dry-matter protein is 10 divided by 20, multiplied by one hundred, which is 50.0 percent. On the pack this wet food looked three times less protein-rich than the kibble; after conversion it comfortably exceeds it. That reversal is the moisture illusion in action.
Now the kibble. Moisture is 8 percent, so dry matter is 92 percent. The dry-matter protein is 30 divided by 92, multiplied by one hundred, about 32.6 percent. Apply the same routine to fat and to the carbohydrate estimate, and the two foods finally sit on common ground. The table gathers a few worked rows so the pattern is clear.
The same conversion applies to fat and ash, which matters because those nutrients are diluted by water in exactly the same way. A wet food showing 5 percent fat at 20 percent dry matter actually carries 25 percent fat on a dry-matter basis, comparable to a fairly rich kibble, a fact the pack hides as thoroughly as it hides the protein gap. Once every nutrient is on dry matter, the carbohydrate estimate by difference becomes meaningful too, and the two foods can be ranked on protein, fat and carbohydrate at once rather than on a single misleading line.
| Food | Crude protein (as fed) | Moisture | Dry matter | Protein on DM |
|---|---|---|---|---|
| Wet food | 10 percent | 80 percent | 20 percent | 50.0 percent |
| Kibble | 30 percent | 8 percent | 92 percent | ~32.6 percent |
| Rich wet food | 12 percent | 78 percent | 22 percent | ~54.5 percent |
| Dense kibble | 36 percent | 9 percent | 91 percent | ~39.6 percent |
| Lean kibble | 24 percent | 10 percent | 90 percent | ~26.7 percent |
Where do the numbers stop and quality begin? {#quality}
Answer capsule: The protein figure measures total nitrogen multiplied by 6.25, not nutritional value. Two foods at the same percentage can differ by more than 15 percent in protein actually absorbed once digestibility is taken into account (FEDIAF, 2024; PubMed reviews, DIAAS score).
Quality lives in three things the panel cannot show: the real digestibility of the amino acids, the essential-amino-acid profile, and the named source. Lean meat often exceeds 90 percent ileal digestibility where some plant or over-cooked proteins drop sharply, and a limiting amino acid caps the use of all the others, so an abundant but unbalanced protein is partly wasted. A named source such as chicken or salmon tells you more than a vague mention of meats or by-products.
The numbers are a starting point, not a verdict. The strongest signals of quality sit beyond the label: a feeding trial under a recognised protocol, the presence of a qualified veterinary nutritionist, and manufacturer transparency, all of which you can check by asking rather than by calculating.
There is also a measure the panel cannot show that often decides real value: digestibility. A protein at 90 percent digestibility supplies more usable amino acids than a higher but poorly absorbed level, and a score such as the DIAAS can even exceed 100 percent for some very complete animal proteins, because it relates the digestible limiting-amino-acid content to a reference profile (PubMed reviews, DIAAS score). None of this appears in the guaranteed analysis, so the panel sets a ceiling on what a food could deliver while digestibility and the amino-acid profile decide how much of that ceiling the animal actually reaches.
What common mistakes distort label reading? {#mistakes}
Answer capsule: The recurring errors are comparing as-fed figures across formats, treating a grain-free claim as a low-carbohydrate signal, and reading the protein percentage as a quality score. Each has a simple correction.
The first and biggest is the moisture illusion: comparing a kibble and a wet food on their printed figures, without dry-matter conversion, makes the wet food look far poorer than it is. The fix is the conversion routine above, applied before any comparison. The second is inferring carbohydrate from marketing: a grain-free food can hold as much carbohydrate as a grain-based one, because pea, potato and tapioca supply plenty, so the level must be estimated by the nitrogen-free extract calculation rather than read off the front of the pack.
The third is mistaking quantity for quality. A high crude-protein figure can come from cheap plant concentrates or low-grade matter, since the measurement counts nitrogen, not value, and two foods at the same percentage can differ markedly in protein actually absorbed. A fourth, subtler error is ignoring ingredient processing: fresh meat loses a large share of its weight on cooking, so an item listed near the top before cooking can make up a more modest share of the finished product. None of these is visible in a single number, which is why the routine pairs calculation with a look at sources and manufacturer transparency.
Recommendation: a reliable reading routine {#recommendation}
Build a fixed routine and apply it every time. Convert each nutrient to a dry-matter basis so kibble and wet food are comparable; estimate the carbohydrate by difference, since the pack will not state it; and, where energy figures allow, relate protein to grams per 1,000 kcal to remove the density distortion. Then stop and remember what the panel cannot tell you: it measures nitrogen and moisture, not digestibility, amino-acid balance or source. Use the figures to rule out the misleading comparisons and to size the food honestly, and use named sources, feeding trials and manufacturer answers to judge the quality the numbers leave out. For a medical diet, let a veterinarian set the targets.
Related questions: How do you fairly compare the protein level of two kibble brands? - How do you convert crude protein to a dry-matter basis? - How do you judge protein quality beyond the percentage?
Related terms: As-fed versus dry matter - Digestibility
Section hub: Protein and macronutrients
Sources: FEDIAF Nutritional Guidelines (2024); Regulation EC 767/2009 (analytical constituents); PubMed reviews on protein quality and the DIAAS score (PMC7590266); WSAVA Global Nutrition Committee (2021).