POLYPHENOLS – Can these plant-derived nutrients really improve your recovery? – Joseph Lillis

Research Spotlight focusses on a single food, nutrient or dietary class that has received recent scientific attention. Joseph Lillis is a PhD researcher at Anglia Ruskin University in Cambridge, who explores the benefits of polyphenols for athletes.

What are polyphenols?

Polyphenols are the most abundant antioxidants in our diet, with over 8000 different varieties classified into four main families: flavonoids, lignans, phenolic acids and stilbenes (1). Widely consumed fruits, vegetables and beverages, such as coffee, tea and wine (2) contain polyphenols; the average 100 grams fresh weight of fruits can contain up to 300 mg of polyphenols (3). Blueberry varieties (836 mg/100 g), blackcurrants (758 mg/100 g) and non-fruit sources, such as cloves and cocoa powder (15,188 mg/100 g and 3448 mg/100 g) (4), offer some of the most generous polyphenol servings. Due to their ubiquitous nature, awareness around a substance’s absorption is key because the most abundant dietary polyphenols do not necessarily possess the greatest bioavailability (5).

How can polyphenols benefit us?

Acting as an antioxidant, the primary role of a polyphenol in the human body is to neutralise free radicals by passing an electron to an unstable atom. This stabilisation will evade a negative set of chain reactions, allowing the human body to maintain the operation of homeostatic processes. Although physical activity and exercise are beneficial to our health and wellbeing, all forms of exercise (particularly intensive exercise) will increase free radical production and cause oxidative stress (the imbalance between free radicals and endogenous antioxidants). An increase in oxygen consumption (e.g. from high intensity or prolonged exercise (6)) can deplete the body’s antioxidant defences and increase the rate of free radical production (7). It is at this point, when an athlete becomes physiologically ‘stressed’ that the body must utilise available antioxidant pathways to minimise the potential of negative responses to training.

In terms of training modalities mentioned in the literature, unaccustomed eccentric or anaerobic exercise appear to contribute to an increase in reactive oxygen species production and reduced antioxidant defences. This may occur due to the induction of inflammatory responses, the combination of which ultimately leads to exercise-induced muscle damage and subsequent muscle soreness (8).

Multiple studies and clinical trials have demonstrated the anti-inflammatory and immunomodulatory responses to individuals exhibiting either a diet high in natural polyphenols, or undergoing an acute supplementation bout of specific polyphenols (9). A proven food-first approach utilising a daily 250 g serving of blueberries for six weeks, on top of a 375 g portion prior to a 2.5 hour run at 72 per cent VO₂max, attenuated exercise-induced oxidative stress (10). Another example demonstrated that 235 ml of tart cherry juice supplemented for 5 days pre- and 48 hours post-marathon run, combated oxidative stress (p<0.05), offered a significant reduction in inflammatory markers (interleukin-6) (p<0.05), as well as a 10 per cent increase in total antioxidant status post run, ultimately leading to a significantly faster recovery of isometric strength (p=0.024) (11).

One indisputable advantage of a superior recovery is the enhanced subsequent exercise performance.

Polyphenols and antioxidant support

Polyphenols have been reported to improve performance by increasing mitochondrial biogenesis in two ways (12): stimulating stress signalling pathways (13) and modulating muscle function via the improvement of flow mediated dilation (12). This is found predominantly in dietary flavonoids such as quercetin (see Table 1), which has shown performance increases of 0.74 – 3.0 per cent following a short supplementation period (14). In sports where the rate of blood flow and maximum cardiac output are important determinants of cardiovascular performance, the consumption of polyphenols prior to training and competition could aid overall athletic performance (12). However, a well-documented caveat to this stems from the supplementation of inorganic compounds, combinations such as vitamin C and E, which may limit training benefits or performance (15,16) when consumed close to training. Consequently, there is a rationale for the supplementation of fruit derived polyphenols to support performance, as well as enhancing recovery from inflammation and oxidative damage present in intensive and strenuous exercise (6).

Currently scientific interest lies with whether polyphenol supplementation may aid the endogenous antioxidant store when fighting the effect of exercise induced oxidative stress.

An excellent review by Bowtell and Kelly pointed out that acute supplementation of ~300 mg of polyphenols one to two hours prior to exercise may be ergogenic, enhancing exercise capacity and/or performance during endurance and high intensity exercise (6). A larger body of evidence suggests that supplementation with >1000 mg of daily polyphenols for >3 days pre- and post-exercise will enhance recovery following exercise induced oxidative stress (6). This could be achieved via ingestion of approximately 450 g fresh blueberries, 120 g fresh blackcurrants or 300 g Montmorency cherries (1). Table 1 exhibits specific polyphenols with potential supplementation strategies.

Table 1: Examples of dietary polyphenols and sport specific supplementation strategies 

Polyphenol take home messages

• A diet rich in polyphenols (fruits, vegetables and derived products) supports potential for an increase in overall health and wellbeing.
• Specific polyphenol supplementation periodised within training blocks may support training quality, but more importantly, reduce recovery time from higher intensity sessions.
• Acute supplementation in the lead up to, and surrounding competition, can offer individual performance benefits.
• The best approach is an informed one, making sure any supplementation has been tried and tested pre-race day.