The effect of prolonged dietary supplementation with guar gum on subsequent iron absorption and retention in rats

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Abstract
1. The effect of prolonged consumption of guar gum on iron absorption and Fe status was investigated in rats. Experiments with closed loops of duodenum, isolated in siru, were designed to reveal changes in the short-term regulation of duodenal Fe uptake, induced by challenge with low- and high-Fe meals. In separate experiments, the effect of guar gum on the capacity of intact rats to maintain Fe status and to absorb Fe from a test-meal was investigated.2. Male Wistar rats were given either a control, semi-synthetic diet (C) for 21 d or a similar diet containing 100 g guar gum (G)/kg for 27 d. Both diets contained 36 mg Fe/kg. Two subgroups were then challenged with meals containing low-Fe (8 mg/kg) or high-Fe (566 mg/kg), while a third subgroup received a meal of the control diet (36 mg Fe/kg). At intervals of 12, 36, 60 and 84 h after the dietary challenge, the uptake of [59Fe] ferric citrate was measured using closed duodenal loops in situ. All G-supplemented animals absorbed less Fe than their C-fed counterparts. Within group C, animals given the high-Fe challenge had lower absorptions 12, 36 and 60 h later, compared with those given the maintenance diet, whilst those given the low-Fe meal showed much increased uptake 12 and 36 h later. The latter effect was virtually abolished by guar gum.3. In the second experiment, male Wistar rats were fed on the C or G diets containing 8, 15, 20, 26 or 36 mg Fe/kg for approximately 10 weeks ad lib. Fe retention from a starch-sucrose test meal extrinsically labelled with 59Fe was then measured, together with packed cell volume and Fe content of the liver as indices of Fe status. No effect of feeding guar gum on Fe retention nor Fe status at any level of Fe intake was observed.4. It was concluded that feeding guar gum leads to a small reduction in the rate of uptake of Fe in the rat duodenum and to an impairment of the regulation of uptake in response to brief episodes of dietary Fe depletion. However, these changes do not apparently lead to any nutritionally significant reduction in the capacity of the intact animals to absorb Fe and maintain their Fe status.