E-numbers / Flavour enhancers / E629
also: Calcium 5'-guanylate · Calcium salt of guanylic acid
A nucleotide flavour booster, the calcium salt of guanylic acid, added to amplify savoury taste in crisps, soups and ready meals.
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Can be produced from fish (sardines), making it a hidden source of fish for people with fish allergies.
Why it’s worth knowing. Can be produced from fish (sardines), making it a hidden source of fish for people with fish allergies. Guanylates are broken down to purines in the body, which raises uric acid levels and can trigger gout attacks with regular intake.
Calcium guanylate is the calcium salt of guanylic acid (5'-GMP), a nucleotide found naturally in all living cells as a building block of RNA. It belongs to the guanylate family of flavour enhancers (E626 to E633). Commercially it is produced from yeast extract or from sardines.
Guanylates bind to umami taste receptors on the tongue and dramatically amplify the perceived savoury intensity of food, particularly when combined with glutamates such as E621 (MSG). The synergy between guanylates and glutamates is well established: together they produce far more flavour enhancement than either compound alone, so manufacturers can use smaller amounts of each. Calcium guanylate contributes no flavour of its own.
Most common in flavoured crisps and snacks, instant noodles, dried and canned soups, stock cubes and bouillon, ready meals, savoury sauces, and processed meat products. It is almost always used alongside MSG or yeast extract rather than alone. On a label it appears as 'calcium guanylate', 'E629', or as part of 'flavour enhancers (E629, E621)'.
Guanylates are nucleotides that the body metabolises to purines and ultimately to uric acid. A sustained high-purine diet raises serum urate levels. For people with gout or hyperuricaemia, nucleotide-rich additives can contribute to the purine load alongside natural sources such as meat, offal and beer. The amounts present in food at typical use levels are small relative to whole-food purine sources, but cumulative intake across multiple processed foods adds up.
Dietary purines, including those from nucleotide additives, are metabolised to uric acid; elevated uric acid is the proximate cause of gout flares.
Guanylic acid and its salts are broken down by the gut to guanosine and then to xanthine and uric acid via xanthine oxidase.
Commercial calcium guanylate is often derived from sardines. Fish is one of the 14 major allergens required to be declared under UK food law. If the production source is fish-derived, the additive could carry residual fish proteins and pose a risk to people with fish allergy. The allergen must be declared on the label, but in practice the origin of the guanylate is not always obvious from the E number alone.
Fish is a declarable allergen under UK food information regulations; any ingredient derived from fish, including flavour enhancers processed from sardines, must be emphasised on the label.
EU and UK food law explicitly prohibits guanylates, including E629, in foods manufactured for infants and young children. The restriction reflects precautionary limits on nucleotide and sodium load in early life diets rather than an identified toxicity signal at adult levels.
Guanylates (E626-E633) are not authorised in foods for infants and young children under the assimilated EU Regulation 1333/2008 Annex II.
People with gout or hyperuricaemia should be aware that guanylates contribute to total daily purine load, especially when multiple processed foods are eaten together. People with fish allergy should check whether the guanylate source is fish-derived, particularly with imports or products whose full allergen chain is unclear. Infants and young children: not permitted in foods made for that age group, so it should not appear on those labels.
Calcium guanylate is a well-characterised nucleotide that has been used in processed food since the 1960s. The body treats it the same way it treats nucleotides from any food source, converting it to uric acid. The real-world question for most people is cumulative purine intake across their whole diet, not this additive in isolation. The fish-origin route is a genuine allergen consideration but is covered by labelling law. For people with gout, multiple processed foods each carrying guanylates alongside naturally high-purine ingredients can be a meaningful combined source. The science here is not live or contested, but the gout and allergen considerations are real and not trivial.
No. Calcium guanylate is approved for use in the UK under the UK FSA approved-additives list (derived from assimilated EU Regulation 1333/2008). It is not permitted in foods for infants and young children, but it is lawful in adult processed foods.
Guanylates are broken down to purines and then to uric acid. For people already managing gout or high uric acid, repeated intake of multiple processed foods containing guanylates adds to the total daily purine load alongside meat, offal and alcohol. Whether it triggers a flare depends on the individual's overall diet and uric acid level.
Most commonly flavoured crisps and snack foods, instant noodles, dried and canned soups, stock cubes, savoury sauces and ready meals. It is rarely used alone and almost always appears alongside MSG (E621) or yeast extract on the label.
Not necessarily. Calcium guanylate is produced commercially from either yeast extract (vegan) or sardines (not vegan, not fish-free). The source is not specified by the E number, so vegans and people with fish allergy should contact the manufacturer or look for products that specify a plant-based source.
Last reviewed: 20 June 2026
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