Effects of Functional Phenolics Dietary Supplementation on Athletes' Performance and Recovery: A Review

many efforts have been made to identify micronutrients or nutritional strategies capable of preventing, or at least, attenuating, exercise-induced muscle damage and oxidative stress, and improving athlete performance. The reason is that most exercises induce various changes in mitochondria and cellular cytosol that lead to the generation of reactive species and free radicals whose accumulation can be harmful to human health. Among them, supplementation with phenolic compounds seems to be a promising approach since their chemical structure, composed of catechol, pyrogallol, and methoxy groups, gives them remarkable health-promoting properties, such as the ability to suppress in ammatory processes, counteract oxidative damage, boost the immune system, and thus, reduce muscle soreness and accelerate recovery. Phenolic compounds have

be harmful to human health. Among them, supplementation with phenolic compounds seems to be a promising approach since their chemical structure, composed of catechol, pyrogallol, and methoxy groups, gives them remarkable health-promoting properties, such as the ability to suppress in ammatory processes, counteract oxidative damage, boost the immune system, and thus, reduce muscle soreness and accelerate recovery. Phenolic compounds have also already been shown to be effective in improving temporal performance and reducing psychological stress and fatigue. Therefore, the aim of this review is to summarize and discuss the current knowledge on the effects of dietary phenolics on physical performance and recovery in athletes and sports practitioners. Overall, the reports show that phenolics exert important bene ts on exercise-induced muscle damage as well as play a biological/physiological role in improving physical performance. Keywords: antioxidant properties; anti-inflammatory effects; phenolic compounds; exercise; recovery; sport performance; football; cycling; athletics 1. Introduction In recent years, special attention has been paid to the incorporation of bioactive in- gredients, especially from medicinal plants, in dietary supplements, nutraceuticals, and pharmaceuticals [1–3]. This is mainly based on the common belief that they are safer and more effective than synthetic drugs, and also due to their lower price, toxicity and side effects [4–8]. Among them, phenolic compounds have been a target of several studies and a hot topic for researchers. They constitute the largest group of secondary metabolites of plants, deriving from phenylpropanoids [1]. Their synthesis involves a series of deamina- tion, hydroxylation, and methylation reactions that are mediated by the shikimate, where phenylpropanoids are formed, and by the acetic acid pathway, where the simplest phenolics are generated [9,10]. Due to their chemical structure, i.e., the presence of catechol, methoxy, and pyrogallol groups, they exhibit remarkable health-promoting properties, namely an- tioxidant, anti-in ammatory, antimutagenic, and vasodilator effects [11,12], which can be considered possible added values in sports' performance and recovery [13–15]. Int. J. Mol. Sci.2022,23, 4652.

Int. J. Mol. Sci.2022,23, 4652 2 of 52 It is undeniable the role of reactive species in human body. In fact, they act as signaling molecules, playing crucial roles in immune responses, regulation, expression, and signal transduction pathways [16,17]. However, and depending on the intensity, duration of the activity, training condition, age, and person gender, training status and genetic pro le, in some situations, physical activities can lead to their overproduction and accumulation, shifting the oxidant/antioxidant ratio in favor of the oxidants, and therefore promote mus- cle soreness and severe ultrastructural damage [16,18–21]. Moreover, in the pre-seasons of most sports, many training sessions are carried out on the same day, leading to the in- creasing production of reactive oxygen and nitrogen species (RNOS) and pro-in ammatory markers [22–24]. For this reason, there is an intense search for ways to mitigate these effects and improve athletes' performance and recovery. There is already evidence that dietary supplementation with phenolics or the regular intake of related dietary sources, such as cereals, fruits, herbs, spices, and vegetables, can offer several advantages given their ability to reduce oxidative stress, and consequently, reduce post-exercise in ammation and immune dysfunction, as well as improve metabolic recovery, aerobic capacity, muscle strength, and viral defense, thus having an interest in different sports with different physi- cal demands [11,14,25–27]. Although the conjugation of phenolics with resistance training has not been adequately studied yet, it has already been shown that acute supplementation with approximately 500 mg of total avonoids or 300 mg of procyanidins per day, 1–2 h before exercise, can effectively enhance athletic performance [28]. In view of the above, the purpose of this paper is to provide a detailed review of the effects of the major dietary sources of phenolics on the performance and recovery of athletes and sports practitioners. This overview is divided into three parts. The first two parts describe the major dietary phenolic sources, their bioavailability, and the relationship between their structure and health benefits. Finally, the third part consists of the latest findings and discussion on the main effects of phenolics in athletes and sports

phenolics on the performance and recovery of athletes and sports practitioners. This overview is divided into three parts. The first two parts describe the major dietary phenolic sources, their bioavailability, and the relationship between their structure and health benefits. Finally, the third part consists of the latest findings and discussion on the main effects of phenolics in athletes and sports practitioners. 2. Data Collection The authors of this review realized an exhaustive and detailed search for relevant articles regarding the potential of phenolics and phenolic-rich sources in sports. For that, data collection was conducted using different accepted scienti c databases, including Google Scholar, Medline (PubMed), National Center for Biotechnology Information (NCBI), ResearchGate, Science Direct, Scopus, SpringerLink, Web of Science and other trusted journals publishes and abstracts until December 2021. The following free-terms, keywords or MeSH terms were applied: phenolics, phenolic-rich sources, phytochemicals, natural products, bioavailability, sports, recovery, performance, competition, antioxidant effects, anti-in ammatory properties, aerobic, anaerobic, demanding sports, athletics, exercises, eccentric exercise-induced muscle damage., and muscle soreness, and combining them with AND, OR, or NOT operators. No hold bars were imposed in terms of author(s) or type of publication during the literature survey. With the exception of one article (Mehri et al. [29]), the other ones were published in the English language. The almost 459 considered publications were carefully read, in order to nd the more recent, complete and/or non-redundant publications meeting the objective of this work. In the nal, there were selected 320 publications to be employed in this review. 3. Phenolic Compounds Medicinal plants, along with cereals, fruits, herbs, and vegetables, are the main sources of phenolic compounds, of which nearly 10,000 have been reported in nature to date [30,31]. They are secondary metabolites produced by plants to protect them from abiotic factors (e.g., drought, extreme temperatures, oods, heavy metals, pH, radiation, salinity, and soils) and biotic factors, such as animals and pathogens attack [32]. In addition, they are considered to be mainly responsible for the organoleptic characteristics (e.g., aroma, avour, and colour) of plants [33]. To facilitate their identi cation, they can be classi ed into ve

protect them from abiotic factors (e.g., drought, extreme temperatures, oods, heavy metals, pH, radiation, salinity, and soils) and biotic factors, such as animals and pathogens attack [32]. In addition, they are considered to be mainly responsible for the organoleptic characteristics (e.g., aroma, avour, and colour) of plants [33]. To facilitate their identi cation, they can be classi ed into ve

Int. J. Mol. Sci.2022,23, 4652 3 of 52 different subgroups based on their structure (at least one phenol ring), namely, (i) phenolic acids (which are further subdivided into hydroxybenzoic and hydroxycinnamic acids), (ii) avonoids (subdivided into avonols, avan-3-ols, avones, avanones, iso avones, a- vanonols, and anthocyanidins), (iii) coumarins, (iv) lignans and (v) stilbenes (Figure) [ 34]. Among them, avonoids are the most abundant in plants [35]. Flavonols are mostly found in apples, berries, grapes, broccoli, lettuce, onions, spinach, and tomatoes, while avan- 3-ols are mainly found in apples, bananas, blueberries, kiwi, peaches, pears, and their juices and jams, cereals, coca, broad beans, lentils, red wine and tea [36–40]. On the other hand, celery, tea, parsley, red pepper, and oranges contain signi cant amounts of avones, while lemons and bitter oranges are rich in avanones [37–39]. Iso avones are mainly found in soy and soy products, lentils, beans and peas, and avanonols, in lemons, grapes, oranges, and mint [36–38,40]. Finally, anthocyanins are largely identi ed in berry fruits and their juices and jams, pigmented cereals, purple corn, red cabbage, and red wine [36,40]. Regarding other phenolics, hydroxybenzoic acids have been reported in berries, onions, and black radish, whereas hydroxycinnamic acids are abundant in apples, berries, pears, plums, artichokes, carrots, chicory, eggplant, lettuce, wheat, and coffee [33,36–38]. Bison, cinnamon, lavender, sweet woodruff, and strawberries contain coumarins, while lignans are mostly found in sesame and axseeds [36,40,41]. Finally, stilbenes are predominant in blueberries, grapes, peanuts, and sorghum [42].Int. J. Mol. Sci. 2022, 23, x FOR PEER REVIEW 4 of 54 Figure 1. Main phenolic compounds. Non-flavonoids comprise coumarins, phenolic acids, lignans and stilbenes, while flavonoids include flavonols, flavan-3-ols, flavones, isoflavones, flavanonols and anthocyanidins. Among them, flavonoids are the most found in nature. Bioavailability of phenolics depends on different processes, including their release from the food matrix, gastrointestinal absorption, and presystemic metabolism; among them, intestinal absorption is considered the rate-limiting step and is the main culprit in reducing the bioavailability [35,54]. It begins in the mouth (Figure 2) with chewing, where the action of the oral microbiota initiates the metabolism of glycosylated compounds [48].

of phenolics depends on different processes, including their release from the food matrix, gastrointestinal absorption, and presystemic metabolism; among them, intestinal absorption is considered the rate-limiting step and is the main culprit in reducing the bioavailability [35,54]. It begins in the mouth (Figure 2) with chewing, where the action of the oral microbiota initiates the metabolism of glycosylated compounds [48]. In the stomach, only a few compounds are hydrolyzed and deconjugated, with most remaining intact [55]. Here, some aglycones and simpler phenolic acids can be absorbed (bioaccessibility) [54]. The other pass to the small intestine, where cleavage and release of aglycones occur by the action of various digestive enzymes, with the activity of cytosolic β-glucosidase and lactase-phlorizin hydrolase being prominent [38]. Then, phenolics can be taken up by passive diffusion or transporters [55]. Some properties, such as lipophilicity, molecular weight, and glycosylation pattern, may affect their transport and permeability [35]. For example, isoflavones and gallic acid are readily absorbed due to their low molecular weight; on the other hand, proanthocyanins must first be degraded due to their high molecular weight [56,57]. The high lipophilicity of aglycones allows them to easily pass through epithelial cells by passive diffusion, whereas polymers, glycosides, and esters cannot pass through the membrane by passive diffusion and require transporters [56]. Quercetin glycosides, for example, require the action of sodium- dependent glucose cotransporter-1, while anthocyanins require glucose transporters 1 and 3 [35,58]. Nevertheless, the greatest absorption rate is observed in the colon [59]. Here, the gut microbiota catalyzes a series of reactions, including decarboxylation, demethylation, dihydroxylation, and hydrolysis, and transforms unabsorbed phenolics into bioavailable metabolites [55]. Usually, flavones and flavanones are degraded to hydroxy- phenylpropionic acids and polymeric phenolic compounds, while anthocyanins and proanthocyanidins are metabolizated to low molecular weight phenolic acids, flavonols converted into hydroxyphenylacetic acids, and flavanols into phenylvalerolactones and hydroxyphenylpropionic acids [52,60]. These acids are further metabolized to benzoic acid derivatives [60,61]. In the liver, they undergo some degree of phase I and/or phase II biotransformation reactions. Phase I includes hydrolysis, oxidation, and reduction reactions carried out by cytochrome P450 enzymes, while phase II

low molecular weight phenolic acids, flavonols converted into hydroxyphenylacetic acids, and flavanols into phenylvalerolactones and hydroxyphenylpropionic acids [52,60]. These acids are further metabolized to benzoic acid derivatives [60,61]. In the liver, they undergo some degree of phase I and/or phase II biotransformation reactions. Phase I includes hydrolysis, oxidation, and reduction reactions carried out by cytochrome P450 enzymes, while phase II aims to increase Figure 1. Main phenolic compounds. Non- avonoids comprise coumarins, phenolic acids, lignans and stilbenes, while avonoids include avonols, avan-3-ols, avones, iso avones, avanonols and anthocyanidins. Among them, avonoids are the most found in nature. As mentioned earlier, their structure (Figure) allows them to readily neutralize free radicals and reactive species, interfere with signaling pathways, and reduce pro- in ammatory markers [4,32,43]. Therefore, it is not surprising that their scienti c interest, consumption, and use in dietary supplements, functional foods, and pharmaceuticals are increasing worldwide [44]. However, although understanding the stability, solubility, bioavailability, and bioactivity of phenolics is not an easy task, it is essential because their health bene ts depend mainly on the amount ingested and bioavailability [45]. In general, the bioavailability of different phenolics varies widely, and the most abundant phenolics in the diet are not necessarily the most activein vivo, either owing to their poor absorption by the intestine, rapid excretion, high metabolism, and/or lower intrinsic activity [38]. Nowa- days, it is estimated that the absorption rates of the most consumed phenolics range from

Int. J. Mol. Sci.2022,23, 4652 4 of 52 2.7–12.2% for lignans, 8–72% for hydroxycinnamic acids, 33–100% for iso avones, 12–41% for avonols and avones, 11–16% for avanones, 2–8% for avan-3-olsand 2.4–55% for anthocyanins [40,46–50]. Nevertheless, some studies reported that these percentages may eventually be higher [49,51]. In an attempt to improve the bioavailability and bioactivity of phenolic compounds, various efforts have been made and discussed. Among the alterna- tives, their encapsulation with carbohydrates (e.g., cellulose derivatives and maltodextrins), lipids (e.g., emulsi ers and waxes), natural gums (e.g., alginates and gum arabic), and/or with proteins (e.g., dairy proteins, gelatin, and soy proteins) seem to be the most promising strategies [45,52]. In addition, it is important to consider that bioavailability rates largely depend on the samples maturity stage, genotype, and agronomic conditions, which in turn, directly in uence phenolic content, food processing, pH, solubility, chemical structure, and sugar moieties [50,53]. Furthermore, it is also important to consider interactions with other components present in food matrix, and the inter-individual variability between individuals (e.g., gender, age, food intolerances, genetic pro le, enzymatic activity, pathological and/or physiological state of intestinal ora), lifestyle, and dietary habits [39,53]. Bioavailability of phenolics depends on different processes, including their release from the food matrix, gastrointestinal absorption, and presystemic metabolism; among them, intestinal absorption is considered the rate-limiting step and is the main culprit in reducing the bioavailability [35,54]. It begins in the mouth (Figure the action of the oral microbiota initiates the metabolism of glycosylated compounds [48]. In the stomach, only a few compounds are hydrolyzed and deconjugated, with most remaining intact [55]. Here, some aglycones and simpler phenolic acids can be absorbed (bioaccessibility) [54]. The other pass to the small intestine, where cleavage and release of aglycones occur by the action of various digestive enzymes, with the activity of cytosolic b-glucosidase and lactase-phlorizin hydrolase being prominent [38]. Then, phenolics can be taken up by passive diffusion or transporters [55]. Some properties, such as lipophilicity, molecular weight, and glycosylation pattern, may affect their transport and permeability [35]. For example, isoflavones and gallic acid are readily absorbed due to their

by the action of various digestive enzymes, with the activity of cytosolic b-glucosidase and lactase-phlorizin hydrolase being prominent [38]. Then, phenolics can be taken up by passive diffusion or transporters [55]. Some properties, such as lipophilicity, molecular weight, and glycosylation pattern, may affect their transport and permeability [35]. For example, isoflavones and gallic acid are readily absorbed due to their low molecular weight; on the other hand, proanthocyanins must first be degraded due to their high molecular weight [56,57]. The high lipophilicity of aglycones allows them to easily pass through epithelial cells by passive diffusion, whereas polymers, glycosides, and esters cannot pass through the membrane by passive diffusion and require transporters [56]. Quercetin glycosides, for example, require the action of sodium- dependent glucose cotransporter-1, while anthocyanins require glucose transporters 1 and 3 [ Nevertheless, the greatest absorption rate is observed in the colon [59]. Here, the gut microbiota catalyzes a series of reactions, including decarboxylation, demethylation, dihydroxylation, and hydrolysis, and transforms unabsorbed phenolics into bioavailable metabolites [55]. Usually, flavones and flavanones are degraded to hydroxy-phenylpropionic acids and polymeric phenolic compounds, while anthocyanins and proanthocyanidins are metabolizated to low molecular weight phenolic acids, flavonols converted into hydrox- yphenylacetic acids, and flavanols into phenylvalerolactones and hydroxyphenylpropionic acids [52,60]. These acids are further metabolized to benzoic acid derivatives [60,61]. In the liver, they undergo some degree of phase I and/or phase II biotransformation reactions. Phase I includes hydrolysis, oxidation, and reduction reactions carried out by cytochrome P450 enzymes, while phase II aims to increase hydrophilicity before excretion [55]. Finally, metabolites may return to the small intestine via enterohepatic recirculation, be further absorbed by enterocytes, and return to the liver, or be eliminated [

Int. J. Mol. Sci.2022,23, 4652 5 of 52Int. J. Mol. Sci. 2022, 23, x FOR PEER REVIEW 5 of 54 hydrophilicity before excretion [55]. Finally, metabolites may return to the small intestine via enterohepatic recirculation, be further absorbed by enterocytes, and return to the liver, or be eliminated [48]. Figure 2. Simplified steps of the metabolic pathways involved in the bioavailability of phenolics in the human body after consumption. CGB—cytosolic β-glucosidase; SULT—sulfotransferase; UDP- GT—glucuronosyltransferase; COMT—catechol-O-methyl transferase; SGLT—sodium-dependent glucose cotransporters; LPH—lactase-phlorizin hydrolase. 4. The Linkage between Phenolics Structure and Health Benefits It is clear from the literature, that phenolics have several beneficial effects on human health, including remarkable antioxidant, vasoactive and anti-inflammatory activities, and the ability to interact with enzymes, and cell receptors [62]. 4.1. Antioxidant Effects of Phenolics Regarding antioxidant mechanisms, different arrangements of functional groups in the core nuclear structure can confer metal chelation, radical scavenging, and/or oxidative activity to phenolics [63]. Although the role of free radicals and RNOS in human metabolism is undeniable, namely in the regulation of gene expression and cell growth, immune responses, and signal transduction pathways, their overproduction and consequent accumulation lead to DNA, lipids and proteins damage, necrosis, and useless inflammatory responses and promote the onset of several diseases, such as cancer, cardiovascular and neurological pathologies [4]. Unlike synthetic antioxidants, whose belief is that their constant intake is harmful and has undesirable effects, phenolics have already shown a notable ability to reduce oxidative stress levels with little or no negative effects [64]. Phenolics are effective in controlling oxidative stress and restoring the redox homeostasis due to their ability to (i) neutralize and/or reduce free radicals and the formation of reactive species, (ii) chelate trace elements involved in the formation of these pro-oxidant species, (iii) modulate the activity of related enzymes in cell signaling cascades, and (iv) stimulate the endogenous defense system by stimulating the action of intracellular antioxidant enzymes (e.g., catalase, glutathione, and superoxide dismutase) Figure 2. Simpli ed steps of the metabolic pathways involved in the bioavailability of phenolics in the human body after consumption. CGB—cytosolicb-glucosidase; SULT—sulfotransferase; UDP- GT—glucuronosyltransferase; COMT—catechol-O-methyl transferase; SGLT—sodium-dependent

(iii) modulate the activity of related enzymes in cell signaling cascades, and (iv) stimulate the endogenous defense system by stimulating the action of intracellular antioxidant enzymes (e.g., catalase, glutathione, and superoxide dismutase) Figure 2. Simpli ed steps of the metabolic pathways involved in the bioavailability of phenolics in the human body after consumption. CGB—cytosolicb-glucosidase; SULT—sulfotransferase; UDP- GT—glucuronosyltransferase; COMT—catechol-O-methyl transferase; SGLT—sodium-dependent glucose cotransporters; LPH—lactase-phlorizin hydrolase. 4. The Linkage between Phenolics Structure and Health Bene ts It is clear from the literature, that phenolics have several bene cial effects on human health, including remarkable antioxidant, vasoactive and anti-in ammatory activities, and the ability to interact with enzymes, and cell receptors [62]. 4.1. Antioxidant Effects of Phenolics Regarding antioxidant mechanisms, different arrangements of functional groups in the core nuclear structure can confer metal chelation, radical scavenging, and/or oxida- tive activity to phenolics [63]. Although the role of free radicals and RNOS in human metabolism is undeniable, namely in the regulation of gene expression and cell growth, im- mune responses, and signal transduction pathways, their overproduction and consequent accumulation lead to DNA, lipids and proteins damage, necrosis, and useless in amma- tory responses and promote the onset of several diseases, such as cancer, cardiovascular and neurological pathologies [4]. Unlike synthetic antioxidants, whose belief is that their constant intake is harmful and has undesirable effects, phenolics have already shown a notable ability to reduce oxidative stress levels with little or no negative effects [64]. Phenolics are effective in controlling oxidative stress and restoring the redox home- ostasis due to their ability to (i) neutralize and/or reduce free radicals and the formation of reactive species, (ii) chelate trace elements involved in the formation of these pro-oxidant species, (iii) modulate the activity of related enzymes in cell signaling cascades, and (iv) stimulate the endogenous defense system by stimulating the action of intracellular antioxidant enzymes (e.g., catalase, glutathione, and superoxide dismutase) [34,65]. In this way, phenolics can decrease the production of pro-apoptotic multidomain effectors Bax and Bak protein, promoting an increase in the ratio of Bcl2–Bcl-xL/Bax–Bak, as well as stimulate the nuclear factor erythroid 2-related factor 2, and

The review discusses the impact of phenolic compounds on athlete performance and recovery.