What “Low Calorie” Actually Means Under UK Law
Red Onion (raw) and Grapefruit (raw) sit two kcal apart in our calculator, 40 versus 42 per 100g. That two-kcal gap also happens to be the exact line UK law draws for whether a food can legally be described as “low calorie.” It’s not a marketing word. It’s a specific, regulated number, and one of these two foods legally clears it while the other doesn’t.
The real number: 40kcal per 100g, or 20kcal per 100ml for drinks
Under Regulation (EC) No 1924/2006 on nutrition and health claims, the exact wording is: “A claim that a food is low in energy, and any claim likely to have the same meaning for the consumer, may only be made where the product does not contain more than 40 kcal (170 kJ)/100 g for solids or more than 20 kcal (80 kJ)/100 ml for liquids.” Not roughly 40. Not “under 50 is close enough.” Forty, exactly, and no more.
That’s also why there are two numbers, not one. A drink is normally drunk in a much bigger portion than a solid food is eaten in, so the regulation sets a lower per-100ml bar for liquids to keep the claim meaningful, rather than letting a genuinely calorie-dense drink squeeze under a threshold built for solids.
Still UK law after Brexit, with one real regional difference
This regulation didn’t disappear when the UK left the EU. In Great Britain it’s now retained EU law, carried over by the Nutrition (Amendment etc.) (EU Exit) Regulations 2019 and 2020, and enforced through the UK’s own system rather than an EU one. In Northern Ireland it still applies directly as EU law, under the terms of the Windsor Framework. Same rule, same numbers, two different legal routes to the same answer.
It governs labelling, not a universal definition of “healthy”
This is a rule about what a business can print on a product’s own packaging or marketing, a specific legal claim with a specific legal test. It’s not a general statement that anything under 40kcal is automatically healthy, or that anything over it isn’t. Plenty of genuinely nutritious foods in our own database, avocado at 160kcal per 100g, almonds at 579, sit well above 40kcal for entirely reasonable, healthy reasons; that’s a different question from whether a food is entitled to carry the words “low calorie.”
Where you’ll see it used on this site
Our own Low Calorie badge, and every Low Calorie hub and category page, use this exact same 40kcal per 100g solid and 20kcal per 100ml liquid threshold, not a rounder, easier internal number. Red Onion (raw), at exactly 40kcal, genuinely qualifies and shows up on our Fruit & Vegetables Low Calorie page; Grapefruit (raw), at 42kcal, genuinely doesn’t, and it won’t appear there. Check both for yourself.
*This article is general information, not legal advice. Food labelling law changes and gets re-interpreted over time, so check an official source directly if you need this for your own business’s compliance.