The positive health effects of phenolic compounds (PCs) have been extensively reported in the literature. An understanding of their bioaccessibility and bioavailability is essential for the elucidation of their health benefits. Before reaching circulation and exerting bioactions in target tissues, numerous interactions take place before and during digestion with either the plant or host's macromolecules that directly impact the organism and modulate their own bioaccessibility and bioavailability. The present work is focused on the gastrointestinal (GI) interactions that are relevant to the absorption and metabolism of PCs and how these interactions impact their pharmacokinetic profiles. Non-digestible cell wall components (fiber) interact intimately with PCs and delay their absorption in the small intestine, instead carrying them to the large intestine. PCs not bound to fiber interact with digestible nutrients in the bolus where they interfere with the digestion and absorption of proteins, carbohydrates, lipids, cholesterol, bile salts and micronutrients through the inhibition of digestive enzymes and enterocyte transporters and the disruption of micelle formation. PCs internalized by enterocytes may reach circulation (through transcellular or paracellular transport), be effluxed back into the lumen (P-glycoprotein, P-gp) or be metabolized by phase I and phase II enzymes. Some PCs can inhibit P-gp or phase I/II enzymes, which can potentially lead to drug-nutrient interactions. The absorption and pharmacokinetic parameters are modified by all of the interactions within the digestive tract and by the presence of other PCs. Undesirable interactions have promoted the development of nanotechnological approaches to promote the bioaccessibility, bioavailability, and bioefficacy of PCs.

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Type-2 diabetes mellitus (T2DM) is an endocrine disease related to impaired/absent insulin signaling. Dietary habits can either promote or mitigate the onset and severity of T2DM. Diets rich in fruits and vegetables have been correlated with a decreased incidence of T2DM, apparently due to their high polyphenol content. Polyphenols are compounds of plant origin with several documented bioactivities related to health promotion. The present review describes the antidiabetic effects of polyphenols, specifically related to the secretion and effects of insulin and glucagon-like peptide 1 (GLP1), an enteric hormone that stimulates postprandial insulin secretion. The evidence suggests that polyphenols from various sources stimulate L-cells to secrete GLP1, increase its half-life by inhibiting dipeptidyl peptidase-4 (DPP4), stimulate β-cells to secrete insulin and stimulate the peripheral response to insulin, increasing the overall effects of the GLP1-insulin axis. The glucose-lowering potential of polyphenols has been evidenced in various acute and chronic models of healthy and diabetic organisms. Some polyphenols appear to exert their effects similarly to pharmaceutical antidiabetics; thus, rigorous clinical trials are needed to fully validate this claim. The broad diversity of polyphenols has not allowed for entirely describing their mechanisms of action, but the evidence advocates for their regular consumption.

Peroxisome proliferator-activated receptors (PPAR) are transcription factors that modulate energy metabolism in liver, adipose tissue and muscle. High fat diets (HFD) can negatively impact PPAR expression or activity, favoring obesity, dyslipidemia, insulin resistance and other conditions. However, polyphenols (PP) found in vegetable foodstuffs are capable of positively modulating this pathway. We therefore focused this review on the possible effects that PP can have on PPAR when administered together with HFD. We found that PP from diverse sources, such as coffee, olives, rice, berries and others, are capable of inducing the expression of genes involved in a decrease of adipose mass, liver and serum lipids and lipid biosynthesis in animal and cell models of HFD. Since cells or gut bacteria can transform PP into different metabolites, it is possible that a synergistic or antagonistic effect ultimately occurs. PP molecules from vegetable sources are an interesting option to maintain or return to a state of energy homeostasis, possibly due to an adequate PPAR expression and activity.

The content of bioactive compounds and antioxidant capacity of nine vegetables of conventional and unconventional utilization in salad mixtures were studied. The total phenolic and flavonoid contents ranged between 39.6–148.5 mg GAE/100g FW and 76.3–217.4 mg QE/100g FW, respectively. Ascorbic acid content ranged between 16.4 and 198.8 mg AAE/100g FW. Antioxidant capacity was assessed using DPPH, FRAP, and ORAC methods; values were in the range of 48.9–245.8 mg TE/100g FW, 67.7–335.8 mg TE/100g FW, and 104.86–833.9 mg TE/100g FW, respectively. Red cabbage, beet greens, parsley, and rocket exhibited the highest antioxidant capacities. Catechin was the most abundant phenolic compound identified in the free fraction, and p‐coumaric acid, quercetin, and caffeic acid in the hydrolyzed fraction. Results suggested that the presence of these phenolics could be of great importance in preventing some chronic and degenerative diseases when regularly consumed. Nonconventional vegetables showed high antioxidant properties, therefore, it is important to promote their consumption. Practical applications Not all vegetables have the same phenolic composition, and not all phenolics have the same antioxidant capacity. Knowledge of the bioactive content and antioxidant capacity profile in each vegetable could be of interest to consumers and the food industry for selecting the more suitable leaves to make salad mixtures with high nutritional and functional values. These compounds can prevent some chronic‐degenerative diseases related to oxidative stress, so it is important introduce them regularly into the diet. Moreover, the evaluation of nontraditional vegetables is intended to bring consumers toward a new source of bioactive compounds, prompting their consumption, and providing added value to certain plant parts that are sometimes considered as waste products.

Obesity is considered to be a low-grade chronic inflammatory process, which is associated with cardiovascular and metabolic diseases. An integral evaluation of the effects of ferulic acid on biomarkers of glucose dysregulation, dyslipidemia, inflammation, and antioxidant potential induced by a high-fat diet (HFD) in rats was carried out. Three groups of male Wistar rats (six per group) consumed a basal diet (BD), which was supplemented with either lard at 310 g/kg (HFD) or lard and ferulic acid at 2 g/kg (HFD + FA), ad libitum for eight weeks. Body weight gain, hyperplasia, and hypertrophy in abdominal fat tissues were higher in the HFD group than in the HFD+FA group. The rats fed a HFD + FA significantly inhibited the increase in plasma lipids and glucose, compared with the HFD group. Biomarkers associated with inflammation were found at higher concentrations in the serum of rats fed a HFD than the HFD + FA group. Plasma antioxidant levels were lower in HFD rats compared to rats fed the HFD + FA. These results suggest that ferulic acid improves the obesogenic status induced by HFD, and we elucidated the integral effects of ferulic acid on a biological system.

The ability of phenolic compounds to cross the blood–brain barrier and reach the central nervous system is discussed. There are knowledge gaps that require additional experimentation, such as inconclusive transport mechanisms and lack of human data.