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Grapefruit Seed Extracts And Health

GSE and its effects on health
GSE and biocides

Back in 2000, Bandolier 73 carried a brief account about how it had looked for trials of grapefruit seed extract and health, and had failed to find any. Grapefruit seed extract (from here on in abbreviated to GSE) is promoted because it kills harmful micro-organisms, based on laboratory tests that demonstrate antimicrobial effects. What was apparent was that manufacturing GSE concentrated antimicrobial preservative chemicals used on grapefruit, and it was likely that it was those chemicals that had the antimicrobial effect.

That small article has attracted almost more email correspondence than any other, so for a bit of peace and quiet, here's an update.

GSE and its effects on health

Bandolier has searched again for studies that demonstrate that eating GSE in any form benefits health. There is none we could find.

Now we might have missed hundreds of good quality randomised trials (a form of publication bias in reverse), but we don't think so. If anyone knows of good evidence, let us know. But we don't want anecdotal accounts of miraculous cures of sick cats, because sick cats often do quite well on their own.

GSE and biocides

The first reference we found was in a Japanese journal [1], in which three compounds were found, two of which were identified as methyl-p-hydroxybenzoate and 2,4,4'-trichloro-2'-hydroxydiphenylether (triclosan). Commercial grapefruit seed extract was quite different from grapefruit seeds, which did not contain these chemicals.

In the second, analysis of six commercial grapefruit seed extracts [2] showed five had antimicrobial properties, and were active against a strain of Candida. In all extracts with antimicrobial activity the chemical benzethonium was found, and, in some, triclosan and methyl parabene.

The US Department of Agriculture has also been doing some investigation of commercial GSE. Their first study [3] found benzethonium chloride. In two GSE samples, the benzethonium chloride amounted to 8% by weight of the GSE sample, so this was no trace constituent. A more recent study [4] found benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride, and benzyldimethylhexadecylammonium chloride, commonly known as benzalkonium chloride.

For the avoidance of doubt, these chemicals are not made by grapefruit. They are synthetic chemicals added to the grapefruit seed extract at some stage. Benzethonium chloride is commonly used in cosmetics and other topical applications, and benzalkonium chloride is widely used as an ingredient in cleaning and disinfectant agents.


Step back a moment from any prior thinking you may have about natural remedies or medicines, about alternative or conventional medicine. Which of us is likely to think that we or a loved one is going to be better off with a nice dose of drain cleaner? Yet right now, the one thing we know is that commercial GSE contains powerful chemicals, but we don't know which ones in which extract, or how much is there. It is a bit like an addict mainlining with strychnine rather than heroin because it is a white powder. The evidence is that GSE without drain cleaner kills no bugs [2].

Yet journalists peddle this stuff in their papers or online all the time. Try GSE for its natural antibacterial action, they say, taken in by the guff and unwilling to do any research. Wake up and smell the drain cleaner.

If journalists want to give safe advice to people who want natural antimicrobials, why not suggest a spoonful of honey? We know honey contains antimicrobial agents, and that it prevents and treats infected wounds, both because of its hyperosmolar nature, and because of these antimicrobials. There is no trial evidence that eating it does any good, but (anecdotally) people with MRSA have cleared it from their system by eating honey. And if the honey were eaten on a slice of wholegrain bread, that would reduce the risk of cancer by about half, as mentioned in Bandolier 53.


  1. S Sakamoto et al. Analysis of components in natural food additive “grapefruit seed extract” by HPLC and LC/MS. Eisei Shikenjo Hokoku 1996: 38-42.
  2. von Woedtke et al. Aspects of the antimicrobial efficacy of grapefruit seed extract and its relation to preservative substances contained. Pharmazie 1999 54: 452-456.
  3. G Takeoka et al. Isolation of benzethonium chloride in commercial grapefruit seed extracts. Journal of Agriculture and Food Chemistry 2001 49: 3316-3320.
  4. GR Takeoka et al. Identification of benzalkonium chloride in commercial grapefruit seed extracts. Journal of Agriculture and Food Chemistry 2005 53: 7630-7636.

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