Assessment of nationally representative dietary studies in the Gulf Cooperation Council: a scoping review

Background Obesity is at a record high in Gulf Cooperation Council (GCC) countries and is expected to continue increasing. Diet is a major contributor to this disease, but there is inadequate nationally representative dietary research from these countries. The aim was to quantify the number dietary studies using food frequency questionnaires (FFQs) that have been conducted in individual GCC countries and to assess the quality of eligible studies. Methodology Four databases (PubMed, Web of Science, MEDLINE, and DOAJ) were searched for keywords; records were screened for eligible studies and data were abstracted on study characteristics (publication year, geographical locations, sample size, units of measurement, number of foods examined, number of Arab foods and key findings). Quality was assessed using an adapted Newcastle-Ottawa Quality Assessment Scale for cross-sectional studies. Results Only seven studies were eligible from four of six GCC countries (Saudi Arabia, Bahrain, Kuwait and Qatar). All eligible studies used FFQs, but only 29% used a validated questionnaire, one being in Arabic, and none of the studies used any additional tools to measure diet. Fifty-seven percent of studies made an effort to include local foods. The majority of studies (71%) either measured frequency or quantity of food consumed, but only 29% attempted to account for both frequency and quantity. Conclusions The quality of studies varied and major weaknesses of FFQ validity and adaptability have been highlighted. More dietary investigations are needed using validated FFQs that have been adapted to the local GCC diets. Using reference tools will allow for better dietary estimations

Quercetin inhibits intestinal iron absorption and ferroportin transporter expression in vivo and in vitro

Balancing systemic iron levels within narrow limits is critical for maintaining human health. There are no known pathways to eliminate excess iron from the body and therefore iron homeostasis is maintained by modifying dietary absorption so that it matches daily obligatory losses. Several dietary factors can modify iron absorption. Polyphenols are plentiful in human diet and many compounds, including quercetin--the most abundant dietary polyphenol--are potent iron chelators. The aim of this study was to investigate the acute and longer-term effects of quercetin on intestinal iron metabolism. Acute exposure of rat duodenal mucosa to quercetin increased apical iron uptake but decreased subsequent basolateral iron efflux into the circulation. Quercetin binds iron between its 3-hydroxyl and 4-carbonyl groups and methylation of the 3-hydroxyl group negated both the increase in apical uptake and the inhibition of basolateral iron release, suggesting that the acute effects of quercetin on iron transport were due to iron chelation. In longer-term studies, rats were administered quercetin by a single gavage and iron transporter expression measured 18 h later. Duodenal FPN expression was decreased in quercetin-treated rats. This effect was recapitulated in Caco-2 cells exposed to quercetin for 18 h. Reporter assays in Caco-2 cells indicated that repression of FPN by quercetin was not a transcriptional event but might be mediated by miRNA interaction with the FPN 3'UTR. Our study highlights a novel mechanism for the regulation of iron bioavailability by dietary polyphenols. Potentially, diets rich in polyphenols might be beneficial for patients groups at risk of iron loading by limiting the rate of intestinal iron absorption

Markers of iron status in control and quercetin-treated rats.

<p>Data are means ± SEM (n). *P<0.05 compared with control group. ^NS Not significantly different from control group.</p

Effects of longer-term exposure to quercetin on iron transport in Caco-2 cells.

<p>Caco-2 cells were exposed to quercetin (10 or 100 µM) for 18 h. Quercetin was removed by washing and cells were incubated in quercetin-free uptake buffer containing ⁵⁹Fe. Uptake across the apical membrane (A) and efflux across the basolateral membrane (B) was determined. Data are mean ± SEM of 5-6 observations in each group. Groups with no common letters are significantly different from each other (one-way ANOVA and Tukey's post hoc test; P<0.05). No letters indicates no significant difference between any of the groups.</p

Effects of quercetin on ferritin protein levels in Caco-2 cells.

<p>Caco-2 cells were exposed to quercetin (10 or 100 µM) for 18 h. Cells were solubilised and aqueous extracts used to measured cell ferritin protein content using a commercially available ELISA. Data are mean ± SEM of 15 observations in each group. Groups with no common letters are significantly different from each other (one-way ANOVA and Tukey's post hoc test; P<0.05).</p

Acute effects of quercetin on intestinal iron transport.

<p>The acute effects of quercetin and its methylated analogues (3MQ, 4′MQ, 3,4′dMQ, PMQ) on iron transport <i>in vivo</i> were measured using the <i>in situ</i> duodenal loop method. ⁵⁹Fe (0.2 mmol/L) and polyphenol (1 mmol/L) were added to the lumenal uptake buffer and mucosal iron uptake (A) and mucosal transfer of iron into the circulation (B) measured. The effects of quercetin on iron uptake across the apical membrane (C) and iron efflux across the basolateral membrane (D) of human intestinal Caco-2 cells was also measured. Data are mean ± SEM of 4 (rat duodenum) or 4–5 (Caco-2 cells) observations in each group. Groups with no common letters are significantly different from each other (one-way ANOVA and Tukey's post hoc test; P<0.05).</p