The current interest in polyphenols has been driven primarily by epidemiological studies. However, to establish conclusive evidence for the effectiveness of dietary polyphenols in disease prevention, it is useful to better define the bioavailability of the polyphenols, so that their biological activity can be evaluated. The bioavailability appears to differ greatly among the various phenolic compounds, and the most abundant ones in our diet are not necessarily those that have the best bioavailability profile. In the present review, we focus on the factors influencing the bioavailability of the polyphenols. Moreover, a critical overview on the difficulties and the controversies of the studies on the bioavailability is discussed.

The lay press often heralds polyphenols as panacea for all sorts of diseases. The rationale is that their antioxidant activity would prevent free radical damage to macromolecules. However, basic and clinical science is showing that the reality is much more complex than this and that several issues, notably content in foodstuff, bioavailability, or in vivo antioxidant activity are yet to be resolved. We summarize the recent findings concerning the effects of polyphenols on human health, analyze the current limitations at pitfalls, and propose future directions for research.

Curcumin, a lipophilic polyphenol contained in the rhizome of Curcuma longa (turmeric), has been used for centuries in traditional Asian medicine, and nowadays it is widely used in food as dietary spice worldwide. It has received considerable attention for its pharmacological activities, which appear to act primarily through anti-inflammatory and antioxidant mechanisms. For this reason, it has been proposed as a tool for the management of many diseases, among which are gastrointestinal and neurological diseases, diabetes, and several types of cancer. However, the pharmacology of curcumin remains to be elucidated; indeed, a discrepancy exists between the well-documented in vitro and in vivo activities of curcumin and its poor bioavailability and chemical instability that should limit any therapeutic effect. Recently, it has been hypothesized that curcumin could exert direct regulative effects primarily in the gastrointestinal tract, where high concentrations of this polyphenol have been detected after oral administration. Consequently, it might be hypothesized that curcumin directly exerts its regulatory effects on the gut microbiota, thus explaining the paradox between its low systemic bioavailability and its wide pharmacological activities. It is well known that the microbiota has several important roles in human physiology, and its composition can be influenced by a multitude of environmental and lifestyle factors. Accordingly, any perturbations in gut microbiome profile or dysbiosis can have a key role in human disease progression. Interestingly, curcumin and its metabolites have been shown to influence the microbiota. It is worth noting that from the interaction between curcumin and microbiota two different phenomena arise: the regulation of intestinal microflora by curcumin and the biotransformation of curcumin by gut microbiota, both of them potentially crucial for curcumin activity. This review summarizes the most recent studies on this topic, highlighting the strong connection between curcumin and gut microbiota, with the final aim of adding new insight into the potential mechanisms by which curcumin exerts its effects.

OBJECTIVE: Insulin resistance (IR) represents an independent risk factor for metabolic, cardiovascular, and neoplastic disorders. Preventing/attenuating IR is a major objective to be reached to preserve population health. Because many insulin-sensitizing drugs have shown unwanted side effects, active harmless compounds are sought after. Dietary anthocyanins have been demonstrated to ameliorate hyperglycemia and insulin sensitivity. This study aimed at investigating whether cyanidin-3-O-β-glucoside (C3G) and its metabolite protocatechuic acid (PCA) might have a role in glucose transport activation in human omental adipocytes and 3T3-L1 cells. RESEARCH DESIGN AND METHODS: In cells treated with 50 µmol/L C3G and 100 µmol/L PCA, [3H]-2-deoxyglucose uptake, GLUT4 translocation by immunoblotting, adiponectin secretion, and peroxisome proliferator–activated receptor-γ (PPARγ) activation by enzyme-linked immunosorbent assay kits were evaluated. Parallel experiments were carried out in murine adipocyte 3T3-L1. To define the role of PPARγ in modulating polyphenol effects, small interfering RNA technique and PPARγ antagonist were used to inhibit transcription factor activity. RESULTS: C3G and PCA increased adipocyte glucose uptake (P < 0.05) and GLUT4 membrane translocation (P < 0.01). Significant increases (P < 0.05) in nuclear PPARγ activity, as well as in adiponectin and GLUT4 expressions (P < 0.01), were also shown. It is interesting that PPARγ inhibition counteracted the polyphenol-induced adiponectin and GLUT4 upregulations, suggesting a direct involvement of PPARγ in this process. CONCLUSIONS: Our study provides evidence that C3G and PCA might exert insulin-like activities by PPARγ activation, evidencing a causal relationship between this transcription factor and adiponectin and GLUT4 upregulation. Dietary polyphenols could be included in the preventive/therapeutic armory against pathological conditions associated with IR.

This work was aimed at producing a sourdough bread that is tolerated by celiac sprue (CS) patients. Selected sourdough lactobacilli had specialized peptidases capable of hydrolyzing Pro-rich peptides, including the 33-mer peptide, the most potent inducer of gut-derived human T-cell lines in CS patients. This epitope, the most important in CS, was hydrolyzed completely after treatment with cells and their cytoplasmic extracts (CE). A sourdough made from a mixture of wheat (30%) and nontoxic oat, millet, and buckwheat flours was started with lactobacilli. After 24 h of fermentation, wheat gliadins and low-molecular-mass, alcohol-soluble polypeptides were hydrolyzed almost totally. Proteins were extracted from sourdough and used to produce a peptic-tryptic digest for in vitro agglutination tests on K 562(S) subclone cells of human origin. The minimal agglutinating activity was ca. 250 times higher than that of doughs chemically acidified or started with baker's yeast. Two types of bread, containing ca. 2 g of gluten, were produced with baker's yeast or lactobacilli and CE and used for an in vivo double-blind acute challenge of CS patients. Thirteen of the 17 patients showed a marked alteration of intestinal permeability after ingestion of baker's yeast bread. When fed the sourdough bread, the same 13 patients had values for excreted rhamnose and lactulose that did not differ significantly from the baseline values. The other 4 of the 17 CS patients did not respond to gluten after ingesting the baker's yeast or sourdough bread. These results showed that a bread biotechnology that uses selected lactobacilli, nontoxic flours, and a long fermentation time is a novel tool for decreasing the level of gluten intolerance in humans.