E-numbers / Flavour enhancers / E640
also: sodium glycinate · aminoacetic acid
A naturally occurring amino acid used in small amounts to add a mild sweet-savoury taste to flavoured drinks and food supplements.
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Glycine is the simplest amino acid, found naturally in many protein-containing foods such as meat, fish, dairy and legumes.
Glycine is the simplest amino acid, found naturally in many protein-containing foods such as meat, fish, dairy and legumes. As a food additive it is produced by chemical synthesis or by hydrolysis of protein sources. The E640 category covers both glycine (E640i) and its sodium salt, sodium glycinate (E640ii).
Glycine acts as a flavour enhancer by contributing a mild, slightly sweet taste with a subtle savoury note. It can round out and balance other flavours, reduce bitterness, and improve overall taste profile. Because it is an amino acid, it also plays a minor role as a flavouring agent in its own right rather than purely amplifying other tastes as monosodium glutamate does.
Most commonly found in flavoured water drinks, sports and energy drinks, protein-enriched beverages, dietary food supplements, and some processed foods where flavour balance is needed. On a UK label it appears as 'glycine', 'E640', 'sodium glycinate', or 'E640ii'.
Glycine is not just a food additive; it is one of the twenty amino acids used to build proteins in the body and is produced naturally in human metabolism. At the amounts used in food (typically below 1g per serving), it is handled by the same metabolic pathways as dietary protein. No adverse effects have been attributed to food-additive-level intakes in healthy adults.
Glycine is a non-essential amino acid synthesised in the body and also obtained from dietary protein; it participates in collagen synthesis, bile acid conjugation, and one-carbon metabolism.
At gram-level doses used in dietary supplements (far above food-additive use), research has explored glycine for sleep quality and cognitive effects. Some small randomised trials found that 3g taken before sleep improved subjective sleep quality. These findings relate to supplement doses, not the trace quantities found in flavoured drinks where E640 functions as an additive.
A small double-blind RCT found that 3g of glycine before bedtime improved subjective sleep quality scores compared to placebo in participants with sleep complaints.
People with rare metabolic disorders affecting amino acid processing should check with a clinician before consuming high-glycine supplements, but food-additive-level exposure in flavoured drinks is unlikely to present a problem even in these cases. Look for 'glycine', 'E640', 'sodium glycinate', or 'E640ii' on the label.
Glycine is one of the most ordinary ingredients a food manufacturer can add. It is the same amino acid your body makes and uses continuously, and it appears in nearly every protein-containing food you eat. The amounts used as a food additive are small relative to normal dietary intake from meat, fish, or dairy. There is no credible published concern about food-additive-level exposure. The supplement literature around glycine is active and largely positive, but that research uses gram-level doses that bear little relation to how much ends up in a flavoured drink.
No. Glycine (E640) is on the UK FSA approved-additives list and is permitted for use in flavoured drinks, dietary supplements, and foods for particular nutritional uses.
Yes, it is the same compound. Protein supplements often contain glycine as a component of collagen or whey hydrolysates. When added as E640 to flavoured drinks, it is present in much smaller amounts and functions as a flavour enhancer rather than a nutritional supplement.
Mainly flavoured and sports drinks, protein-enriched beverages, and dietary food supplements. It is less commonly used in everyday supermarket food than many other flavour enhancers. Check for 'glycine', 'E640', or 'sodium glycinate' in the ingredients list.
Commercial E640 is produced by chemical synthesis or by hydrolysis of protein sources; the synthetic route is vegan, but protein-hydrolysis routes may use animal-derived protein. Manufacturers do not routinely declare the production route on-pack, so strict vegans may wish to contact the manufacturer directly.
Last reviewed: 20 June 2026
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