The Mediterranean diet in Spain: adherence trends during the past two decades using the Mediterranean Adequacy Index.

OBJECTIVE: The purpose of the present study was to analyse the evolution of the Spanish population's global and regional adherence to the Mediterranean diet (MD) since 1987. DESIGN: A cross-sectional study was conducted analysing food consumption from the Spanish Household Consumption Surveys administered by the Spanish Ministry of Agriculture, Fisheries and Food. SETTING: The Mediterranean Adequacy Index (MAI) was applied to measure the adherence to the MD. The significance of the MAI trend was evaluated using a regression model. SUBJECTS: The sample comprises a household consumption data set, which consisted of 2500 households in 1987 and increased to 6200 in 2005. RESULTS: There was a significant decrease in the MAI (P=0.001) during the past two decades in Spanish households. From 1987 to 1997, MD adherence significantly decreased, but since 1998 it appears to have stabilised. In recent years, the daily household availability of several of the food components of the MD has increased. The MAI was observed to be significantly higher during the entire period in some Mediterranean regions, such as Andalusia, and significantly lower in more inland regions, such as Castile-Leon. CONCLUSIONS: During the past two decades, Spain has experienced a significant downward trend in adherence to the predominant dietary pattern, likely as a result of numerous socio-economic changes. However, a stabilisation and a recent slight recovery have been observed during the past decade.

Key role of aldosterone and pericryptal myofibroblast growth in colonic permeability.

When sodium intake diminishes, both the kidney and distal colon contribute directly to sodium homeostasis. In response to a diet with low amounts of sodium, the body hormonal profile changes to produce different effects on crypt-colon permeability and absorption and in the pericryptal sheath surrounding distal colonic crypts. This adaptation produces an increase in Na absorption, a decreased crypt-wall permeability, and an activation of the growth of pericryptal myofibroblasts. The separate roles of the 2 main hormones implicated in the process, aldosterone and angiotensin II, until now have been unclear. Experiments conducted on adrenalectomized rats on low- and high-sodium diets, implanted with osmotic pumps perfusing either aldosterone or angiotensin II, allow us to discriminate between the effects of these hormones. In the distal colon, aldosterone acts as a trophic agent on the myofibroblasts layer and is the key hormone controlling colonic permeability, but angiotensin II alone has no discernable direct role in the process.

Role of vasopressin in rat distal colon function.

The specific role of vasopressin in colonic crypt function and its possible synergistic action with aldosterone were studied. Sprague-Dawley rats fed a high-Na+ (HS; 150 mM NaCl) or a low-Na+ (LS; 150 microM NaCl) diet were deprived of water or infused with vasopressin, and some animals were treated with specific vasopressin receptor subtype V1 and V2 antagonists. The expression of the epithelial Na+ channel (ENaC), alpha-smooth muscle actin (alpha-SMA) and aquaporin-2 (AQP-2) were determined by immunolocalization in distal colonic mucosa. The pericryptal Na+ concentration was determined by confocal microscopy, using a low-affinity Na+-sensitive fluorescent dye (sodium red) and crypt permeability was measured by the rate of escape of fluorescein isothiocyanate-labelled dextran (10 kDa) from the crypt lumen into the pericryptal space in isolated rat distal colonic mucosa. A high plasma concentration of vasopressin raised alpha-SMA expression in the pericryptal sheath (P < 0.05), increased the pericryptal Na+ accumulation in this space (P < 0.01) and caused a reduction of crypt wall permeability (P < 0.01). All these effects were reversed by selective blockade of V1 and V2 receptors. No synergistic effects with aldosterone were observed. Dehydration and vasopressin infusion increased AQP-2 expression in distal colonic mucosa (P < 0.05). This action of vasopressin was prevented by tolvaptan, a specific V2 receptor antagonist (P < 0.05). It is concluded that vasopressin has trophic effects in the rat distal colon, increasing pericryptal myofibroblast growth which affects crypt absorption, and these effects are independent of the presence of aldosterone.