Irn-Bru Original uses Aspartame (E951) and Acesulfame K (E950) in place of some of the sugar. A single can (330ml) contains 168 kcal and 40.3g of sugar.
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Irn-Bru Original contains 51 kcal, 12.2g of carbohydrate (12.2g sugar) and 0.04g of salt per 100ml.
Irn-Bru is Scotland's most-sold grocery product and the UK's fourth-largest cola brand by volume. Its distinctive flavour comes in part from ammonium ferric citrate (iron ammonium citrate), which the brand once used to claim Irn-Bru was 'made in Scotland from girders'. At 12.2g of sugar per 100ml, it is in the upper Sugar Tax levy band and has one of the highest sugar concentrations of any mainstream UK soft drink. Unlike cola and many other CSDs, it is caffeine-free.
Irn-Bru Original contains 12.2g of sugar per 100ml, placing it in the upper levy band under the Soft Drinks Industry Levy. A single can (330ml) delivers 40.3g of sugar, 134% of the adult daily free sugar limit.
Irn-Bru Original uses Aspartame (E951) and Acesulfame K (E950) in place of some of the sugar, with multiple sweeteners blended to better replicate the taste of sugar than any single sweetener can alone. Sweeteners deliver a sweet taste without the calories of sugar, but they are not nutritionally neutral — the evidence on their effects is more nuanced than most drinks marketing acknowledges.
In 2023 the World Health Organization issued a formal advisory recommending against using non-sugar sweeteners for weight control, stating that the long-term evidence does not show they help people manage weight or reduce the risk of obesity-related conditions. The WHO classified its guidance as a conditional recommendation, reflecting that the evidence is still emerging, but the direction is clear: sweeteners are not a straightforward healthy alternative to sugar.
A growing body of research suggests artificial sweeteners may disrupt the gut microbiome, the community of bacteria in the digestive tract that plays a role in metabolism, immunity and mood regulation. A 2022 study published in Cell found that sucralose, saccharin and stevia altered gut bacterial composition in healthy adults, with individual responses varying significantly. The long-term significance of these microbiome changes is not yet established, but the findings support treating sweeteners as active food compounds rather than inert additives.
Sweeteners may also affect appetite regulation. Because they stimulate sweet taste receptors without delivering the expected calories, some research suggests the brain's reward response to sweet taste becomes partially decoupled from energy intake over time. The evidence here is contested: some studies find sweetener users compensate by eating more elsewhere, while others find no effect. What is clear is that sweetened drinks, whether sugar-sweetened or sweetener-sweetened, are associated in epidemiological data with continued desire for sweet-tasting foods rather than reducing it.
Aspartame breaks down in the body into phenylalanine, aspartic acid and methanol. For most people, these metabolites are processed normally. However, people with phenylketonuria (PKU) cannot metabolise phenylalanine safely, which is why any product containing aspartame is legally required to carry the warning 'Contains a source of phenylalanine' on the label. In July 2023, IARC (the WHO's cancer research agency) classified aspartame as 'possibly carcinogenic to humans' (Group 2B) — the same classification as aloe vera extract and coffee — while simultaneously the Joint WHO/FAO Expert Committee on Food Additives confirmed the existing Acceptable Daily Intake (40mg per kilogram of body weight per day) remains safe. The two bodies are not contradicting each other: Group 2B means there is limited evidence of possible risk, not that consumption at normal levels is dangerous.
None of this means sweetener-containing drinks are dangerous at normal levels of consumption. Regulatory agencies in the UK, EU and worldwide continue to approve sweeteners at current dietary intake levels. The more useful question for daily nutrition decisions is whether drinks using sweeteners are genuinely better than the alternatives. The honest answer: a sweetener-containing drink is likely lower in calories and sugar than the full-sugar equivalent, but is probably not as neutral as drinking water, and should not be treated as a free pass to unlimited consumption.
People with phenylketonuria (PKU) must avoid Irn-Bru Original due to its aspartame content.
Nutrition information from official brand UK nutrition panels, Coca-Cola GB nutrition pages, UK retailer product listings, and independent nutritionist analyses. Figures per 100ml; per-serving values are proportional estimates. Sugar Tax (SDIL) status based on UK sugar content thresholds at time of writing — brands may reformulate. Caffeine figures from EU/UK mandatory nutrition labelling. Reference intakes: EU Reference Intakes for an average adult (2,000 kcal). Fruit juice is subject to the SDIL if it contains added sugar; pure juices exempt. For guidance only, not medical advice.