Polyphenols: what they are, what foods contain them and why polyphenols are important

What are polyphenols?

Polyphenols are compounds found in plants and they can be categorised into four main groups called lignans, phenolic acids, stilbenes, and flavonoids.

What do polyphenols do and which foods contain them?

Polyphenols are responsible for the bright colours of plants and they have several other essential roles, including growth, pollination, and resistance to foreign invaders (pathogens).

Interest in their role in human health is linked to their protective role in plants, and research has shown how polyphenols can help reduce the risk of disease through their role as an antioxidant and anti-inflammatory in the body. Those most widely researched are fruit-derived polyphenols sourced from cherries, blueberries, blackberries and pomegranate, which are all rich sources.

Food is always the preferred source of nutrients in the diet and any research relating to polyphenols helps strengthen the recommendation of more fruits and vegetables. Despite this, the average Brit just about manages to eat four servings of fruit and vegetables, with only 30% consuming five-a-day. Most of the research regarding polyphenols centres around specific extracts and their role in supporting recovery and performance in athletes, so they involve using supplements.

Why are polyphenols important?

Many studies link polyphenols to recovery, including an extensive review of the evidence published in the journal Sports Medicine. This review highlighted that polyphenols’ role as an antioxidant and anti-inflammatory might help to reduce the oxidative stress, inflammation and muscle pain associated with muscle damage induced by exercise, leading to faster recovery.

Further studies have also shown how polyphenols may help to reduce muscle soreness and enhance recovery after exercise. Sleep is an integral part of the recovery process and studies have also linked the use of tart cherries to improved sleep, although the research is carried out on a specific type of cherry called Montmorency.

Immunity is vital for any athlete as they can be more predisposed to upper respiratory tract infections (URTIs), interrupting their training and hamper performance. Flavonoids may help to reduce the incidence of URTIs in healthy adults, according to research published in the journal Advances in Nutrition, which showed a 33% decrease in the incidence of URTI in those who supplemented with flavonoids compared to a control. This said, the effect of flavonoids on URTIs in athletes specifically is yet to be thoroughly studied.

Several studies have linked certain polyphenols to performance, including the consumption of anthocyanins, which are blue pigments found in blueberries and other blue and purple fruits and vegetables.

Is there any evidence to link polyphenol supplements to improved performance?

While supplements use extracts of the fruit for their polyphenol content, many of them do not show the exact content of the active compound, which makes it difficult to determine the dosage. There also remains little consensus on the specific doses of fruit polyphenols. Again, it’s tricky to decide how much to consume, so athletes are encouraged to have a wide range of brightly coloured fruit and vegetables in their diet.

To infer the desired effect, the polyphenols extracted from a fruit must be the same as those investigated, so choosing cherry juice, for example, is not going to be relevant if it is not either Montmorency or Balaton varieties.

Regardless of this, there is some research for their use in performance.

• Blackcurrant (New Zealand-derived) powders and concentrated juices have been studied concerning their anti-inflammatory actions and influence cardiovascular adaptations and blood flow. Findings have suggested a very slight improvement in high-intensity exercise lasting between 15-30 minutes.
• Tart cherries (Montmorency and Balaton) supplied as a concentrated gel shot have been explored for their performance benefits, but the results are mixed at best. One study published in the journal Current Sports and Medicine Reports showed an enhancement in the recovery of strength and the reduced muscle soreness following intense exercise or endurance events that resulted in muscle damage. It appeared to be particularly beneficial when events span several days (try Healthspan Elite Performance Cherry Juice – £44.99 for 30 sachets).

• Quercetin is a polyphenol found in foods such as red grapes, apples, citrus fruits and green leafy vegetables, and can also be seen as a supplement in capsule form. According to research published in the journal Medicine and Science in Sports and Exercise, quercetin improves endurance performance when 1,000mg/day is consumed for at least seven days (try Healthspan Elite Quercetin 1000mg – £29.99 for 90 capsules).

Are there any risks with increasing your polyphenol intake?

To achieve the levels of polyphenols used in many of the studies, you would need to consume around 150g of blueberries or 300g of mixed berries, which poses no risk to health. Increasing the amount of fruit and vegetables you eat is good, but be aware that some fruits may act as a laxative, such as cherries and other berries.

This may be an issue for endurance athletes such as cyclists who may need a greater intake of polyphenols to support recovery. Using supplements alongside fruits and vegetables can help avoid gut distress.

Using supplements may also cause digestive upset in some people, so they must be used with caution and thoroughly tested to see how your body reacts during training and competition. Research has also suggested that consuming high doses of antioxidants and anti-inflammatory compounds may reduce the adaptive response to exercise training. Taking high-dose supplements during day-to-day training is not advisable to help encourage adaptations to exercise in the body.

Polyphenols have a beneficial role in our health and maintaining optimal health is critical for athletic performance. Supplements may have a role to play regarding performance and recovery outcomes among athletes. Still, they should be used with caution and alongside advice from a sports nutritionist, while they may also be of more benefit to those involved in endurance sporting events.

References

1. Somerville, V., Bringans, C., & Braakhuis, A. (2017). Polyphenols and performance: A systematic review and meta-analysis. Sports Med, 47, 1589-1599.
2. Bowtell, J., Kelly, V. (2019). Fruit-derived polyphenol supplementation for athlete recovery and performance. Sports Med, 49, S3-S23.

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