How do I read the protein number on a food label?
Check which basis the figure uses before anything else: per 100 g is for comparing products, per serving is for planning your day, and the serving on the pack is often not the amount you eat. Front-of-pack claims like high in protein are legally defined by the share of energy from protein, not by the grams.
Key takeaways
- Per 100 g compares products. Per serving plans your day. Reading one as the other is the most common label mistake.
- The serving size on the pack is a manufacturer's choice, and it is frequently smaller than a portion anyone eats.
- In the EU and UK, source of protein and high in protein are defined by the percentage of energy from protein, not by grams.
- A high protein claim on an energy-dense food can be satisfied while the grams stay modest.
- A barcode scan reads the declared figure, which is why packaged food is the one case where tracking is exact rather than estimated.
Packaged food is the one place your protein number is not an estimate. It is a declared figure with a legal basis behind it, which makes it the most accurate entry you will ever log. The catch is that several different numbers appear on the same box.
Check the basis first
Before reading the figure, find out what it is a figure of.
| What it is for | Where it misleads | |
|---|---|---|
| Per 100 g or 100 ml | Comparing two products against each other | It is not a portion. 100 g of a dense food is a lot; 100 ml of a drink is a mouthful |
| Per serving | Planning your own day | The serving is the manufacturer's choice, and often smaller than anyone eats |
| As prepared | Nothing much | It usually includes the milk you add, so the protein is partly yours |
The per 100 g column is required on EU and UK packaging and is the one to compare with. Everything else on the pack is a marketing decision about presentation.
The serving size trap is worth dwelling on. A pack of four yoghurts declares per pot, which is honest. A bag of granola declares per 45 g, which is about a third of what most people pour. Both figures are accurate and only one of them describes your breakfast.
What "high in protein" actually means
Front-of-pack claims are regulated, and the rule is not what most people assume.
- Source of protein: at least 12 percent of the food's energy comes from protein.
- High in protein: at least 20 percent of the food's energy comes from protein.
Both are ratios, not amounts.2 That single fact explains most of the confusing labels in a supermarket.
Two consequences follow, and they run in opposite directions.
A "high protein" food can carry very little protein. If the food is low in calories overall, 20 percent of a small number is a small number. A high protein drink at 60 kcal per bottle clears the bar with about 3 g.
A genuinely protein-rich food can fail the test. Add fat or sugar and the denominator grows. Cheese, nuts and many protein bars carry real protein per serving while the percentage of energy from it falls below the threshold, because the rest of the energy is fat.
So the claim tells you about the composition of the food, and the grams tell you about your day. Only one of those is on your target.
Where the numbers come from
For packaged food, the manufacturer calculates the declared value from the recipe or has it analysed, and it is an average with a legal tolerance around it rather than a measurement of the item in your hand. That is more than good enough: the variation is small next to the variation in how much of an unpackaged food you served yourself.
For unpackaged food there is no label, and the reference figures in this library come from the USDA's FoodData Central.1 Those are population averages for a food, which is a different kind of number from a declared label value and should be treated as slightly softer.
The practical upshot
Two habits cover almost everything.
- Compare on per 100 g. Log on per serving, adjusted to what you actually took. If you poured double the stated serving, log double.
- Read the back, not the front. The claim on the front is a legal statement about ratios. The panel on the back is the number you need.
This is also why scanning a barcode is the only exactly precise logging method there is: it reads the declared figure straight off the product rather than estimating anything. How the logging methods differ goes through when each one is the right tool, and packaged food is the easy case in all of them.
More questions about Protein basics
What does high in protein legally mean?
In the EU and UK it means at least 20 percent of the food's energy comes from protein. Source of protein is the lower tier, at 12 percent. Both are ratios rather than amounts, so a food can qualify while carrying few grams per serving, and a food with plenty of protein per serving can fail to qualify if it is also high in fat or sugar.
Why does the front of the pack say something different from the back?
Usually because they use different bases. The front often quotes a serving, or a serving prepared a particular way, such as a shake made with milk. The back is required to carry per 100 g. Compare products on the per 100 g column and use the per serving figure only for your own day.
Should I trust the number?
For packaged food, broadly yes: it is a declared figure with a legal basis, and it is the most accurate protein number you will get without a laboratory. Tolerances exist and the value is typically an average for the recipe, but it is far better than an estimate of a plate of food.
