Green tea has received a fair amount of research attention in recent years, with scientists looking to demonstrate the impact that its high polyphenol content might have on health. Polyphenols are organic chemicals found in plants, which have various different properties, eg anti-inflammatory, anti-oxidant. Another area that green tea has been linked with is fat burning, which explains why there are a heap of supplements out there containing green tea extract and implying that you can become leaner if you take them, particularly before a workout. So should endurance athletes be taking green tea supplements or drinking copious quantities of green tea itself in their quest for ‘marginal gains’ in performance?The start of 2015 has seen the publication of the positive results from a randomised placebo-controlled trial on decaffeinated green tea supplements in recreational cyclists 1 which certainly suggests it’s worth taking a closer look at the topic. On the other hand, the conclusions of a number of other papers published in the last year or two have not shown the same. As so often with research, more and bigger studies are required to draw more definitive conclusions and, in particular, more studies need to be conducted in recreationally trained athletes – rather than overweight sedentary people – so you can make a reasonable assumption that you yourself might see a response to green tea supplementation.
The benefits of drinking green tea on certain aspects of health are pretty well established after many research studies. The polyphenols in green tea, the most abundant of which is epigallocatechin gallate (EGCG), have been shown to help reduce cholesterol, triglycerides and blood pressure, for example. Another constituent of green tea, the amino acid l-theanine, has been shown to increase the activity of the anti-anxiety neurotransmitter GABA and levels of the ‘pleasure’ neurotransmitter dopamine. Green tea has been shown to help to reduce free radical damage that results in oxidative stress, an underlying contributor towards many health conditions.
Both black and green tea has been shown to have an anti-inflammatory effect, but it is greater from green tea due to the higher amount of polyphenols it contains. Black tea is green tea that has been oxidised by a fermentation process, which reduces its active constituents. Green tea is also considerably lower in caffeine than both coffee and black tea, which makes it a useful drink if you are trying to reduce your caffeine intake generally or just in the period prior to a race so that you may be more responsive to caffeine consumed during your event. So leaving the question of fat oxidation aside for the moment, I do recommend that all endurance athletes consider including green tea drinks in their diet on a regular basis. This doesn’t have to be a hot drink; several new ready-to-drink green teas have appeared in chiller cabinets recently as an alternative to other soft drinks (but look for one with low sugar content). You also need to check the green tea percentage in the individual tea bag; this should be around 60-80%. The matcha type of green tea has particularly high polyphenol content.
Recently, attention has turned to the potential impact of green tea – in extract form – as an aid to fat oxidation and therefore metabolic efficiency – the intensity you can work at while still burning fat as fuel , thus sparing carbohydrate stores. A 2013 review paper 2 looked at the efficacy of increased fat oxidation rates found in some (but not all) earlier studies and the potential mechanisms that might explain the results. The authors concluded that the varying results might be related to study design differences, bioavailability of green tea extract in humans, and inconsistencies in the way fat oxidation was measured. They also proposed that the changes to fat metabolism that followed the ingestion of green tea extract occurred as a result of alterations in molecular signalling pathways, such as PPAR-γ coactivator 1α (also known as PGC1- α), at least when green tea extract was consumed consistently for a duration of weeks rather than as a single dose. The same research group then carried out a study on active male cyclists published in 2014 3 which showed that green tea extract did not significantly change whole-body fat oxidation rates compared with placebo, regardless of whether the extract was taken was taken for 1 day, 7 days or 28 days.
I’ll now turn to the study published in January this year 1, which had rather different results. In this case, 14 recreational cyclists were given decaffeinated green tea extract (containing 400mg of the EGCG polyphenol) or placebo for four weeks. They were instructed to cycle three times a week for one hour at 50% of VO2 max and to eat a standardised diet (45% carbs, 31% protein, 23% fat) on the day before each of three 40 minute time trials, which took place in weeks 0, 2 and 4. Body weight decreased by the same amount in both green tea extract and placebo groups. But body fat % only dropped in the green tea extract group (by an average 1.63%). Fat oxidation rates increased by almost 25% over the 4 weeks in the green tea extract group, but was unchanged in the placebo group. And, perhaps, most relevant to endurance athletes, the green tea extract group covered 10.9% more distance in the TT at week 4 compared with the TT at week 0. So a true performance benefit was seen, and this was not coming from caffeine as a decaffeinated extract was used; this variable was not always controlled for in other studies. The researchers concluded that taking decaffeinated green tea extract led to more efficient use of fat as fuel and less reliance on carbohydrate. Glycogen stores were therefore preserved for longer and improved exercise output resulted.
So should you rush out and buy some green tea extract? This is just one study, with a small number of participants, although it appears well designed. Bigger studies using the same protocol are needed to confirm the result. It’s also worth noting that participants were not following the higher fat, lower carbohydrate diet often recommended to improve metabolic efficiency. Response to these types of supplements is also very individual, based on your genetic make-up, training status, etc so you may well find that decaffeinated green tea extract has no effect on your performance. But, based on the latest study, it might be worth a try, especially if becoming less reliant on carbohydrate for fuel is one of your goals. And do consider drinking some green tea on a regular basis for its health benefits.
Jo Scott-Dalgleish BSc (Hons) is a BANT Registered Nutritionist, writing and giving talks about nutrition for endurance sport. Based in London, she also works as a Registered Nutritional Therapist, conducting one–to–one consultations with triathletes, distance runners and cyclists to help them eat well, be healthy and perform better through the creation of an individual nutritional plan. To learn more about these consultations, please visit www.nutritionforendurancesports.co.uk
1 Roberts et al. The effect of a decaffeinated green tea extract formula on fat oxidation, body composition and exercise performance. J Int Soc Sports Nutr. 2015 Jan 21:12 (1):1
2 Hodgson AB, Randell RK and Jeukendrup AE. The effect of green tea extract on fat oxidation at rest and during exercise: evidence of efficacy and proposed mechanisms. Adv Nutr. 2013. Mar 1; 4(2):129-40
3 Randell et al. Variable duration of decaffeinated green tea extract ingestion on exercise metabolism. Med Sci Sports Exerc. 2014. Jun; 46(6):1185-93