After water, tea is the most widely consumed beverage in the world. It is grown in over 30 countries and enjoyed worldwide (1). Most tea sold is black, but about 20% is green tea.
Green tea contains high concentrations of biologically active compounds that can affect your health. A lot of people know that green tea is healthy, but did you know that it can help you to lose weight?
If you look at most weight loss supplements, green tea extract is usually listed as an ingredient. So how does this work, and how much tea do you need to drink to achieve this effect?
This article will answer these questions, so you can get a clear idea of how green tea can help you lose weight.
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What Is Green Tea?
The same tea plant – Camellia sinensis – is used to make both black and green tea. The difference is the amount of processing. Being exposed to the air induces chemical changes called oxidation – the same process that turns iron to rust.
Green tea has had the least oxidation and other processing out of the tea varieties. The compounds that are being oxidized are called polyphenols.
One group of polyphenols, catechins, is largely responsible for the health benefits of green tea. Green tea consists of up to 30% catechins by weight, far more than in black tea.
Black tea has under half of the catechins as green tea (2).
Catechins have a wide variety of biological effects within your body. They are potent antioxidants, for starters. Antioxidants neutralize harmful chemical species called free radicals. These exist naturally in your body as a byproduct of metabolism but are highly chemically reactive. Too many of them can damage your tissues, which is a problem because modern lifestyles can lead to overproduction.
Catechins also have other activities – they help to form new blood vessels and prevent blood clots, for example. As a result, the benefits of catechins to your cardiovascular health are well-established (3). This means that green tea can help keep you healthy – but can it help you lose weight?
The weight-loss claims surrounding green tea catechins are mostly based on the activity of one specific catechin, epigallocatechin gallate (EGCG). EGCG can boost your metabolism, meaning you burn energy faster (4). It can also reduce your appetite.
In a study using rats, researchers found that EGCG reduced food intake and body weight, while other catechins did not (5).
Another study shows that EGCG reduces glucose production by the liver (6). The liver stores and releases sugar depending on the body’s energy needs. The proper functioning of this system is important for metabolism and fat burning. These effects show us that EGCG can potentially work as a fat-burning aid, but do not prove that green tea itself is a fat burner. For that, we have to take a longer look at what else is in green tea, and how it all works together.
Effects Of Green Tea
Green Tea Increases Your Metabolism
The first way green tea helps you lose weight is to boost your metabolism. Your body burns energy constantly, whether you’re at rest or running a marathon. Increasing your resting metabolism means your baseline level of energy-burning is higher. Fat burning depends on the energy balance of your body – how many calories are coming in and how many are going out?
Burning more energy at rest helps achieve a positive balance that stimulates fat burning.
Catechins are partially responsible for this, but green tea contains caffeine as well. An average cup of green tea contains around 30-50 mg of caffeine, about a quarter of what a cup of coffee has. Plenty of evidence supports caffeine’s role in boosting metabolism. Caffeine consumption can increase your resting metabolic rate by 3-11% (7, 8).
Meanwhile, an 8-week study of healthy volunteers showed that catechins from green tea increased metabolism during rest (9). The combination means that green tea extracts are proven to increase your resting metabolic rate. Multiple studies show a modest boost of around 4% at rest (10, 11).
Green Tea Boosts Norepinephrine
Caffeine and EGCG also interact with the sympathetic nervous system. This system’s major hormone and neurotransmitter is norepinephrine (noradrenaline). Norepinephrine has stimulating effects. It increases heart rate, and therefore, metabolism (12), and stimulates fat burning in fatty tissues (13). It also promotes the release of stored sugar in the body to boost energy, allowing more energy for exercise and activity (14).
Researchers have demonstrated that EGCG inhibits an enzyme called COMT that breaks down norepinephrine. The result is increased levels of norepinephrine in the blood (15).
Caffeine is also known to increase levels of norepinephrine through its stimulating activity – but the sum of these effects can’t account for the observed level of fat burning green tea promotes. So what is going on?
Some scientists think that the caffeine and catechins in green tea have a synergistic effect that promotes fat burning.
In a laboratory study with healthy volunteers, one group was given green tea extract, and the other was given a placebo. Norepinephrine levels, measured in the urine, were 40% higher in the treatment group. This resulted in a 4% increase in fat burning during the test period (16).
Green Tea Increases The Benefits Of Exercise
It’s great that green tea increases fat burning and metabolism at rest, but the effects are modest. The most significant benefits of green tea for weight loss come when it is combined with other healthy lifestyle choices – like exercising. Caffeine is great to take before exercise because it reduces your perceived exertion, helping you to exercise longer and harder. One study showed that caffeine improved exercise performance by 11.2% (17).
We have already seen that EGCG helps release energy for work by burning fat and regulating sugar release. The combined effect of the compounds within green tea significantly increases fat burning during exercise.
A volunteer group of healthy men was given either green tea extract or a placebo and asked to complete a 30-minute cycling task. The men who took the extract burned 17% more fat after the exercise than the control group (18).
When fat is released from fat cells, the energy enters the bloodstream, where it can be used by the body for work.
Green Tea May Reduce Fat Absorption
The primary fat-burning action of green tea is increasing the number of calories burned by the body. There is also some evidence that green tea extract can reduce the amount of fat absorbed from foods. This effect has mostly been studied in vitro – outside the body, using extracts of enzymes from animals.
Green tea extract significantly reduced the activity of fat-digesting enzymes in one study (19). These enzymes were extracted from the duodenum and intestines. Theoretically, this could mean that catechins or other green tea compounds result in more fat passing through the body undigested.
Another study showed that polyphenols in green tea slowed down the emulsification of olive oil. Emulsification is the packaging of fat molecules in water-soluble bubbles so they can be digested by our bodies (20).
As more research is conducted into this effect, we’ll know more about whether it happens this way in our bodies or not.
Does Green Tea Actually Increase Weight Loss?
There are several reasons why green tea can theoretically help you to burn fat. But does it work in practice? A review of the evidence shows that green tea compounds result in a modest but sustainable reduction in weight. Across 11 studies that met the criteria for inclusion in the review, subjects lost an average of 1.31 kg. Usually, this weight was lost over a 12-week period and was a long-lasting effect (21).
The lost fat was more often the kind called visceral fat, or belly fat. While most fat is located underneath the skin and is harmless or even protective, belly fat builds up around the organs and presents increased risks from high blood pressure, heart disease, and diabetes (22).
Catechins specifically increase the burning of this type of fat, especially in conjunction with exercise. This happened even when overall weight loss was negligible (23).
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How To Best Use Green Tea For Weight Loss
You may have noticed that most of these studies mentioned have been conducted with green tea extract, not green tea itself. Can drinking the tea get you enough of the active compounds to produce an effect, or are you better off with the extract?
100 mg of EGCG taken as a supplement is about equivalent to having 1-2 cups of brewed green tea (24). The amount of catechins and EGCG taken by subjects in the studies above varies.
In the study showing that EGCG increased metabolism, subjects took 570.4 mg of total catechins, of which 218.4 mg was EGCG (9). That’s equivalent to 2-4 cups of green tea. One of the studies showing a 4% improvement in metabolic rate at rest used a range of EGCG doses. These ranged from 270-1200 mg per day.
While 1200 mg is an unrealistic amount of EGCG to get from drinking tea (12-24 cups), the effect was the same as the group of received just 270 mg (3-6 cups) (10).
Catechins can be destroyed by boiling water. When brewing green tea, you should use water slightly below boiling temperature, either by boiling the water and letting it sit for a few minutes or by mixing it with cold.
One study found that the antioxidant content of brewed green tea was highest when brewing with water at 90°C/194°F and after brewing for five minutes.
You may also want to consider matcha green tea as an alternative to the standard kind. This is a powdered form of the green tea leaf that has a higher concentration of catechins. The amount of EGCG in matcha green tea is at least three times higher than regular green tea and could be as much as 137 times higher than some brands (26).
Drinking green tea two hours before bedtime is common advice. The idea is that your metabolic rate is lowest while you are sleeping, so you have the most to gain from using the tea to increase it. However, the caffeine may keep you awake if you have it right before going to sleep.
As discussed above, caffeine helps you to exercise harder and longer, so drinking green tea half an hour before a workout is a good way to gain these benefits. Green tea shouldn’t be consumed on an empty stomach first thing in the morning, because the caffeine can cause excessive stimulation or dehydration in these cases.
Green tea can help you lose weight. It does this by increasing the number of calories you burn, both at rest and during exercise. It also specifically promotes fat burning by working on the sympathetic nervous system.
The fat burned is more likely to be harmful fat that accumulates around the organs, rather than the healthy fat that is stored under the skin. This effect is relatively modest, so don’t expect green tea to be a miracle cure.
Rather, green tea should be a part of a balanced weight loss regime that includes a healthy diet and regular exercise. Green tea even works the best for weight loss when combined with exercise. The caffeine allows you to do more intense workouts and go for longer, while the fat-burning effects of the catechins are more effective when exercising.
A few cups of green tea per day are enough to experience these effects, but the brand of green tea you drink and the way you brew it are important too.
Green tea supplements and matcha green tea are handy ways to ensure a good dose of catechins.