Watercress and Sport Performance
Prepared for The Watercress Company by Lucy Williamson Nutrition, April 2019
There is mounting evidence for the consumption of nutrients beneficial for sports performance, including enhanced recovery post exercise and the maintenance of an optimal immune system, often compromised due to the oxidative stress of sport, with upper respiratory infections often problematic for sportsmen and women. Ultimately, a fast return to training is key. With the growing interest in plant-based diets, this review looks at key nutrients which are of particular benefit in sport and how watercress can be a valuable source.
It’s also worth noting that in the field of elite sport, the World Anti-Doping Agency encourages athletes to find natural food solutions where possible to reduce the risk of inadvertently taking prohibited substances from contaminated supplements.
Our everyday metabolism uses oxygen. By-products of this process are known as free radicals, which can cause damage to cells in a process known as Oxidative Stress. We produce antioxidants all the time in our cells which remove these radicals, keep our cells healthy, protect us from long-term illness and slow down the ageing process. Generally, our in-built antioxidants keep Oxidative Stress under control but during intense physical exercise, we’re exposed to stressors for a longer period, potentially damaging muscle protein, therefore affecting sports recovery. In this situation our antioxidant need is higher, therefore additional antioxidants from our food become important. (Chuang et al 2017). We also know that oxidative stress is a precursor to chronic illness such as heart disease and cancer; oxidation of cholesterol ‘packages’ within the blood stream causing damage to blood vessel walls and oxidation of cell DNA being a possible precursor to cancer. Foods which have the potential to enhance our own mechanisms in combatting oxidative stress, are of real benefit in sport.
Isothiocyanates (ITCs) are a type of glucosinolate antioxidant in Brassicas. Specifically, studies have shown Phenethylisothiocyanate (PEITC), of which watercress contains the highest levels of all brassicas, to be pivotal in detoxification after oxidative stress (Gründemann et al 2018). Read more about the role of watercress in phase II detoxification here. https://www.thewatercresscompany.com/phase-ii-detoxification
Vitamin C is required to make many of our antioxidants in addition to its own antioxidant role; the detail above explaining why there is a higher demand for Vitamin C during and after intense physical exercise, to combat oxidative stress.
100g of watercress contains more Vitamin C than an orange!
Our immune system has a high demand for energy due to constant cell multiplication. Vitamin C is pivotal here in providing this energy source through activating the enzyme, Carnitine, required in this process. Research has also demonstrated its essential role in enabling immune cells to kill bacteria and to recover afterwards and also in the chemical signalling pathway which attracts immune system cells to the area in the body that needs them. A good intake of Vitamin C is therefore essential during intense training when the immune system is susceptible to the effects of oxidative stress. (Carr et al 2017)
By influencing gene expression, Vitamin A is essential in our production of cells required for a strong immune response to infection. Not only is it responsible for the cells of our immune system which circulate in the bloodstream, but it also has a role in the barrier effect of the cells lining our gut and respiratory system in resisting infection. Watercress is high in Vitamin A, with 100g providing 50% of our recommended nutrient intake; even better – its Vitamin A enhances iron absorption.
Iron is essential for all energy-requiring processes in the body, as well as its role transporting oxygen in the haemoglobin of red blood cells. Watercress not only contains more iron than spinach and other leafy greens but crucially its high levels of Vitamin C ensure its iron can be absorbed. Unlike iron from meat and fish sources (known as ‘haem iron’) which is readily absorbed by the body, iron from plant sources (‘non-haem iron’) has to be transformed by Vitamin C into the haem form, in order to be bioavailable. This is crucial for sports enthusiasts following a vegetarian or vegan diet and with an increased demand for iron. With the trend towards more plant-based eating, understanding the need for Vitamin C in iron absorption becomes extremely important; watercress therefore provides the ideal plant source of iron.
Watercress, like beetroot, is rich in nitrates. Research is showing an association between nitrate-rich vegetables and the efficiency of oxygen usage during intense physical activity, specifically, improved exercise performance and longer time to exhaustion (Reid 2013) (Thompson et al 2015). The cells lining our blood vessels, endothelial cells, constantly produce nitrous oxide which is required to maintain optimal blood pressure and protect against inflammatory conditions within blood vessels – the precursor to cardiovascular disease and stroke. High-nitrate foods have the potential to enhance our own supply of nitrous oxide and therefore help regulate blood pressure, which in turn optimises oxygen usage during sport. For example, beetroot juice is shown to improve cycle trial and 5K running performances. Optimum doses are not yet established, but 0.5L of a high-nitrate juice for the 5 – 6 days before competition, taken 3 hours before training, has been suggested as a dose to optimise their nitrate benefits. (Cermack et al 2012). Research on the potential role of watercress in this field is ongoing.
Watercress is a plant source which is naturally high in protein; its protein content contributes 54.5% of its energy value. (BNF 2018) research later in 2019.
Gut Health and Sport Performance:
Our gut microbiota, the trillions of bacteria present in our large intestine, are now known to be pivotal in our health. With more than 3 million genes between them (our gut microbiome), compared to our own 20,000, their potential for influencing the day to day functioning of our body and therefore our health, is clear.
With regard to sports performance, gut bacteria are vital in the correct development and functioning of our Immune System and have a key role in our response to the oxidative stress associated with exercise. Additionally, in harvesting energy from the fibre in our food, promoting digestion and nutrient absorption, they have a pivotal role to play in efficient energy use required in sport. Tim Spector, Professor of Genetic Epidemiology at King’s College, London, also promotes the benefits of a healthy microbiome in sport as a contributor to faster performances, improved recovery and protection against respiratory infection and gastrointestinal problems that can get in the way of training programs.
Watercress for enhancing Gut Bacteria:
Watercress contains natural bacteria which can only benefit our own microbiome. It is also one of the richest sources of polyphenol antioxidants as detailed above, and a source of dietary fibre. Our gut microbes have a pivotal role in transforming these polyphenols into their active metabolites, for example those that will be required to combat the oxidative stress associated with sport. But this relationship between polyphenol antioxidants and gut bacteria is mutually beneficial – research has shown that these same polyphenols inhibit the growth of unfavourable bacteria therefore allowing optimum gut bacteria to flourish. This two-way interaction between polyphenols and the gut microbes is therefore not only of benefit in sport but in our long-term health too, with gut bacteria being key in health outcomes such as Type 2 Diabetes, inflammatory conditions such as Inflammatory Bowel Disease, Colon Cancer, cardiovascular disease and depression. (Rankin et al 2017, Hsu et al 2015)
Hsu et al, 2015 were the first to show the beneficial effects of the microbiome in exercise performance during their research on different colonies of mice, one group being ‘bacteria free’ and the other having strains of beneficial gut bacteria. Endurance exercise was longer and antioxidant activity higher in those mice with a beneficial microbiome.
In their research on exercise and the microbiome, Rankin et al (2015) note that moderate exercise has a beneficial effect on inflammatory conditions such as Rheumatoid Arthritis. This is known to be mediated by the Vagus nerve, which is, in effect, the ‘hard-wiring’ of the gut. Currently it is thought that metabolites produced by gut microbes are influential on the functioning of the vagus nerve, otherwise known as the ‘gut-brain’ axis.
Fig. 1, courtesy of O’Sullivan et al 2015, shows potential areas in which the microbiome may be influential in sport.
Emerging research is suggesting key micro-nutrients and bioactive substances as described above, have a pivotal role in sports performance. Watercress is a rich source of Vitamin C and A, as well as having the highest brassica content of the polyphenol antioxidant PEITC. Its potential as a source of protein and nitrates as well as its pre and probiotic function are an exciting area of development. A low sugar, low fat and low salt food, watercress has great potential in the field of nutrition for sports performance.