Can drinking green tea actually raise your metabolism?
Hailed for millennia for its health-boosting properties, drinking green tea for weight loss is one of those long-standing health food claims that rears its head every few years.
According to legend, the brew was first discovered by the mythological Emperor Shennong in China in 2737 BC. Today, it's a firm favourite of the Hollywood elite. Jennifer Lopez has it before performances, Gwyneth Paltrow has said she won't leave the house without a cup, and Jennifer Aniston drinks it throughout the day.
Surprisingly maybe, given the taste, appearance and reputation, green tea originates from the same tea plant as your standard cuppa, the Camellia Sinensis. During the production of black tea, the leaves are allowed to oxidise, which nixes many of the plant's health-boosting properties. Green tea leaves are unoxidised, so they keep high levels of micronutrients that are packed with antioxidants, known as polyphenols.
These health credentials have seen green tea mooted as an aid for everything from headaches to dementia. But, though the brew is undoubtedly good for you, know that while these claims – including that it might help with losing weight – generally have a kernel of truth to them, it's not quite a total health panacea.
Green tea for weight loss: does it work?
There have been a huge number of studies investigating the weight-loss properties of green tea and generally, in trials ranging between six weeks and six months, they've reported largely positive – although not statistically significant – effects on weight loss and fat composition. It's key to note that in these, participants are generally given green tea supplements, rather than cups to drink.
"Green tea acts by slightly raising metabolism and preferentially burning fat," explains Dr Carrie Ruxton, who has a PhD in Child Nutrition and works with the Tea Advisory Panel. It's believed these effects are due to the high level of catechins, principally EGCG, which is potently antioxidant and aids weight loss through thermogenesis, a process of heat production in the body.
It also contains caffeine, which has been proven to encourage lipid oxidation – aka fat burning – and to improve exercise performance.
"To lose weight and burn fat, your body must first break it down and move it into your bloodstream," explains David Wiener, training specialist at Freeletics. "The compounds in green tea can help aid this process by boosting the effects of some fat-burning hormones, such as norepinephrine (noradrenaline). EGCG is extremely helpful in inhibiting an enzyme that breaks down the hormone norepinephrine, which increases the amount of norepinephrine, promoting fat breakdown."
A 2012 analysis found that green tea did aid weight loss in overweight or obese people, but that this was "statistically non‐significant" – so, nothing to get too carried away with.
A 2020 meta-analysis of studies carried out on the impact of green tea (again, these trials gave participants green tea supplements, rather than cups to drink) on obese people found that a daily habit lowered body weight by just under 2kg over 12 weeks. "We suggest that the use of green tea can be combined with a balanced and healthy diet and regular physical exercise in the management of obese patients," concluded the authors of the analysis. "This is a modest reduction," says Dr Ruxton, "which is why green tea works best when combined with healthy eating and sensible portion sizes."
How much green tea should I drink?
Studies have varied how much is consumed, but it’s generally thought to be between 2-4 cups daily. It’s served without milk or sugar, so it’s calorie-free and can be a good alternative to unhealthy drinks. Much as is often used in trials, you could also take a green pill supplement, rather than drinking brews.
Which green tea is best for weight loss?
It doesn’t matter which brand you drink, but "when choosing which tea is best for you, opt for minimally processed and natural green tea as this will always the best for your health," says Wiener.
Avoid bottled green teas, which can contain added sugar or sweeteners.
How is green tea extract for weight loss?
If you don't like a classic cup of green tea, green tea extracts have been proven to have similar benefits. One study on 63 obese adults found a 7.3lb increase in weight loss and 183 more calories burned a day over three months.
When is the best time to drink green tea for weight loss?
There haven't been many studies into specific hours for consumption, so opinions on the prime time vary. The good thing is that it means you can just have it when you feel like it; for some that will be the morning, instead of your flat white, but others will find it a handy perk-up in the early afternoon.
"I would say morning and early afternoon to enable the green tea polyphenols to work alongside your normal activities," says Dr Ruxton. "Exercise and green tea are a powerful combination as both raise metabolic rate and target fat burning."
As with any caffeinated drinks, try to avoid drinking green tea directly before you go to bed. "This is because it contains the amino acid L-Theanine which makes you more alert and awake, which aids concentrate but disrupts sleep." says Wiener.
Is green tea good for working out?
Green tea is proven to be particularly effective for weight loss when combined with exercise. As well as the caffeine improving performance, research shows consumption prior to a workout can help burn 17 per cent more fat. Another showed EGCG can lead to lower levels of body fat in the longer term, though their focus group was obese men.
Wiener explains: "If you consume green tea before working out, these antioxidant compounds can increase your fat-burning during cardio exercise, as well as continuing to burn calories at rest, helping you burn more than you would with exercise alone."
How should I prepare green tea for weight loss?
"When making yourself a cup of green tea, make sure to not overheat the water, as excess boiling will damage the catechins," Wiener recommends. "For best results, boil water and then allow it to rest for 10 minutes. Then pour it over the tea leaves and let it sit for a couple of minutes before straining the leaves."
Are there disadvantages of drinking green tea every day?
It's a source of caffeine, so "if you have caffeine sensitivities, you could experience insomnia, anxiety, irritability, nausea, or an upset stomach," says Wiener. "It is also a diuretic, which makes it ideal for treating and combating fluid retention but, if you drink it too much, it can also be harmful."
Otherwise, when consumed sensibly, it's natural and healthy.
Speak to your GP before starting any new diets or taking any new supplements, especially if you're on medication. And don't start one solely to lose weight as you can do that more effectively by eating healthily and exercising regularly.
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