f246 Guar, Guar gum

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This gummy substance, obtained from the ground endosperm of the seeds of a tree, is used mainly as a thickener and stabiliser in commercial food processing. Three or 4 species of Guar are found in regions of Africa, Arabia, India, Pakistan, the USA, and northern Australia (1).

IgE-mediated reactions

Food-induced anaphylaxis has been reported (2).

Workers in textile, cosmetics, and fireworks manufacturing, the food and pharmaceutical industries, hairdressing, printing, and mining are at risk for occupational allergy. Allergic rhinitis and palateal oedema were reported in 3 individuals. Two were exposed to fine Guar gum powder upon opening cables in a power cable laboratory. (Guar gum is used as an insulator in rubber cables.) After 1-2 years' exposure, the patients developed rhinitis. The 3rd subject developed allergic rhinitis from exposure to Guar gum in a paper factory after 2 years' exposure. Skin-specific IgE to Guar was detected, and nasal provocation tests confirmed the diagnosis (3).

Rhinitis and asthma have also been reported in staff working in a pharmaceutical company and at a carpet manufacturing plant. Specific IgE was demonstrated on skin tests, and high levels were found in their serum to Guar gum. Specific inhalation challenges in which the 3 subjects were exposed to powder of Guar gum elicited isolated immediate bronchospasm in 2 subjects and an immediate and a delayed reaction in the 3rd subject (4).

Other studies have substantiated Guar gum as an occupational allergen in carpet manufacturing. Fourteen of 162 employees at a carpet manufacturing plant using Guar gum were shown to be sensitised to this gum, 2 of which had occupational asthma. Skin-specific IgE to Guar gum was demonstrated in 8 workers (5%), and 11 (8.3%) were found to have specific IgE to Guar gum in their blood (5).

In 15 subjects with occupational asthma—8 due to high-molecular-weight agents (flour and Guar gum) and 7 due to isocyanates—inhaling occupational agents of high or low molecular weight through the mouth or nose resulted in asthmatic symptoms. Significant nasal symptoms and an increase in nasal resistance occurred, as well as significant changes in inflammatory cells and mediators(6).

Sixteen workers with normal nonspecific bronchial reactivity (NSBR) who had been previously diagnosed with occupational asthma caused by high-molecular-weight agents—flour in 7 workers, psyllium in 5, and Guar gum in 4—were re-challenged after removal from exposure to these agents for a mean of 5-7 years. They no longer showed evidence of asthma and had a normal lung function. The authors conclude that specific bronchial reactivity to high-molecular-weight agents persists in most cases despite a normalisation of NSBR, and that this persistence is associated with a persistence of specific immunisation to the agent(7).

Reversible obstructive sleep apnoea as a result of occupational exposure to Guar gum powder in a pet food plant employee has been reported. Severe cough, rhinitis, and conjunctivitis were also experienced (8).

Other reactions

Excess intake of Guar gum may result in nausea, flatulence, abdominal cramps, and diarrhoea. Guar gum readily absorbs water and swells, and should thus not be ingested as a dry powder. There is a limit on the use of Guar gum in slimming capsules, since it could cause oesophageal obstruction as a result of swelling up in the oesophagus rather than the stomach, causing choking or even rupture of the oesophagus.

Guar gum is used as a thickener in foods and infant foods. The ingestion of Carob bean gum caused a significant reduction in the absorption and bioavailability of calcium, iron, and zinc (9).

No allergens from this plant have yet been fully characterized.

Guar gum and Carob bean flour are both derived from Leguminosae plants. The molecular structures of Carob bean and Guar gum are very similar, consisting of a high-molecular-weight polysaccharide (a galactomannan, composed of galactan and mannan units, with a ratio of 1:4 for Carob and 1:2 for Guar) (10).

Cross-reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected but in fact is not seen frequently (11). In an in vitro study, the specific IgE binding by protein extracts of 11 food legumes was examined by RAST and AST inhibition. Cross-allergenicity was demonstrated to be most marked among the extracts of Peanut, Garden pea, Chick pea, and Soybean (12-14). However, clinical studies have found that there is little cross-reactivity among members of the Fabaceae (Leguminosae) (14, 15).

Last reviewed:April 2022