Tea ranks after water as the most consumed fluid worldwide and has always been promoted as a healthy beverage.
Although Black tea is more popular, Green tea is considered a healthier option rich in antioxidants.
I am sure you must have heard about the weight loss benefits of Green Tea.
It has always been touted as an effective beverage for weight loss along with its numerous health benefits. It is said to burn fat and increase metabolism.
But, is it really the wonder beverage that can help you lose weight?
Here you will read the scientific evidence behind the green tea weight loss claims along with its nutritional makeup.
Weight Loss effects of Catechins and Caffeine in Green Tea (Studies)
The health benefits of green tea are due to the biochemical properties and bioavailability of the constituents in tea. It is rich in antioxidants known as polyphenol.
Polyphenols are naturally occurring compounds found in fruits, vegetables and beverages. Plants have polyphenols for defence against ultraviolet radiation and aggressive pathogens.
Catechins are the major group of polyphenols in Green Tea. Epigallocatechin gallate (EGCG) is the major form of tea catechin along with epicatechin gallate (ECG), epigallocatechin, and epicatechin and other polyphenols.
It also contains some amount of Caffeine along with lower quantities of polyphenols.
About 2.5 gms of green tea in 250 ml of water (a typical serving of green tea), there is about 240-320 mg of Catechins of which 60-65 percent is EGCG and 20-25 mg is Caffeine.
The catechins mainly EGCG and caffeine are the primary ingredients that cause the weight loss effect of the green tea.
As per the Meta-analysis published in 2015 following are a few important studies on the topic-
In about 26 randomized controlled trials (1,2) the Green Tea Extracts combined with Caffeine produced some reduction in weight owing to BMI (Body Mass Index) and waist circumference of test subjects. These included 8-12 weeks of studies with overweight and normal-weight individuals.
The key findings here were that Green Tea extracts alone were not as effective as the Caffeine and Green Tea Extract mixtures. Also, results differed for subjects with different ethnicity and caffeine intake habits.
Another study with moderately overweight Chinese subjects over 90 days period with daily consumption of 458–886 mg of green tea catechins found a reduction in body fat levels. (3)
Green Tea Extract and Caffeine mixture has also shown to increase the metabolism and oxidation of fat in test subjects. (4,5) Metabolism is the rate at which our body digests and assimilates the nutrients of the food while higher fat oxidation would imply that catechin-caffeine mixture in green tea does improve fat loss to some extent.
However, there have been a few instances where Green Tea does not prove to be of any consequence with a fat loss like in a study with English adult subjects with a high dosage of green tea and caffeine had no significant effect on fat oxidation, resting energy expenditure and body composition. (8)
The cause of these differences in results can be attributed to the difference in physiology and eating habits of individuals.
Effects of Green Tea have been extensively studied in rodents on high-fat diets or genetically obese/diabetic animal models.
Most of the studies showed that the consumption of green tea extracts (GTE) or EGCG significantly reduced the body weight, lowered blood glucose or insulin levels, and increased insulin sensitivity or glucose tolerance.
This implies that green tea antioxidants primarily EGCG can help reduce the fat and help regulate the insulin hormone level and improve its sensitivity which plays a major role in the deposition of fat in the body.
For instance, 16 weeks of EGCG treatment on mice with a high-fat diet saw a reduction in body weight gain, body fat and visceral fat weight. (9)
Similarly, a reduction in liver fat accumulation along with lowering of body weight was also seen in mice fed with a high-fat diet. (10)
Most of the observed beneficial effects of Green Tea are believed to be due to the polyphenols, although caffeine also contributes to some of the effects.
The subjects in these studies were mostly supplied high dosage of green tea extracts per day and the responses remain to be substantiated and are a topic of further investigations.
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How Does Green Tea Help in Weight Loss?
1) Inhibits Digestion and Absorption of Nutrients
Weight Loss in green tea is proposed to be an implication of inhibition of the digestive process in the body.
Nutrients like fats upon ingestion are emulsified, hydrolyzed and absorbed in the small intestine. This process is interrupted by green tea polyphenols mainly EGCG.
Some studies also show similar effects on glucose absorption as the EGCG has an inhibitory function on enzymes like amylase that are involved in the digestion of carbohydrates in the body. (14)
Although similar effects of polyphenols on protein digestion have not been extensively studied and require further investigations.
2) Effects on Intestinal Microbes
Green tea is said to possibly affect the probiotic environment in the intestine.
Research on 10 volunteers for a period of 7 days was done to analyse the bacteria profile of there faecal samples after having green tea. It was observed that there was a change in healthy gut bacteria population in the colon. (15)
A similar study on mice also proved that green tea helped to increase the Lactobacillus in the intestine and attenuated the high-fat induced inflammation. (16)
There is yet more research needed to prove that having green tea daily can act as probiotics for the gut and help reduce the inflammation.
3) Effect on Metabolism
Research proposes that most of the effects of green tea on metabolism are characterized by energy-sensing molecules, such as AMPK (5′ adenosine monophosphate-activated protein kinase ).
AMPK is an enzyme that responds to different hormone signals in the body to maintain the energy balance by making more energy available for the cells through catabolism or breakdown activity. (17)
The AMPK hypothesis suggests that EGCG mediates the action of AMPK in the liver, skeletal muscle, adipose tissue and pancreas.
AMPK promotes catabolism i.e. breakdown of glucose and fatty acids in the body in response to energy falling status.
4) Effect on Hormones
The hormones Epinephrine and Norepinephrine are released in the body of animals and humans under the condition of stress. They increase the delivery of oxygen to the muscles and release of energy.
This explains the increased energy expenditure and fat oxidation in humans.
5) Caffeine Content
Although present in small amounts Caffeine is an active constituent of green tea.
It is also reported to induce the AMPK in muscles which promote the breakdown of fatty acids. (24)
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Green Tea Dosage as a Weight Loss Beverage
There are many studies that show the weight loss effects of green tea and oxidation of fat tissue along with an increase in metabolism.
Does that mean you can now sip cups of green tea and forget about Diet and Exercise to lose weight?
There is no substitute for regular exercise and a healthy diet for achieving fat loss.
Green tea can only aid in the process.
Also, most of these studies have considered green tea extracts or the concentrated form of green tea that contain EGCG and other catechins in high amount.
This means that the weight loss effect of green tea can only be seen when you consume at least 3 to 4 cups of it per day. Even then you might find results at the minuscule level.
You should also consider that green tea, when consumed on an empty stomach in large amounts, is known to cause irritation in the gastrointestinal system.
Inhibition of the digestion and absorption of many nutrients is one of the way catechins help in weight loss. Hence you must also prohibit yourself with an overdose of green tea which may lead to nutrient deficiency in the body.
Taking a high concentration of green tea extract as a dietary supplement has been known to cause liver toxicity.
Keep in mind that the dose and response of the green and its health benefits have yet not been fully prescribed in studies and many of these studies have concluded with non-human test subjects.
This is not to deter you from trying out the green tea in your daily diet. Green Tea has several other health benefits along with aiding in weight loss.
Switching to having green tea instead of beverages with sugar content can definitely help you tame those extra calories and help you lose weight.
Calories in a cup of Green Tea
Green Tea is often considered to have zero calories.
It mainly consists of polyphenols, caffeine, minerals, and trace amounts of vitamins, amino acids, and carbohydrates.
Although there are no traces of fats present in Green tea, a cup may contain 1 or 2 calories. But that is not a significant number.
So yes, a cup of green tea prepared in water is literally calorie-free.
This means that the calorie content of green tea largely depends on the substances added to it during the preparation.
For Instance, when you add 1 teaspoon of sugar in a cup of green tea with water you would add approx 15 calories to it.
Green tea with a teaspoon of honey would give you an average of 22 calories.
Bottled green tea available in the supermarkets may contain added flavours and sugar along with preservative. It would have much higher calorie content and defeats the purpose of having green tea as a health drink.
When to Drink Green Tea for Weight Loss
For an effective aid in weight loss, you must consume at least 3 to 4 cups of green tea in a day.
But timing these cups would determine your state throughout the day and in the long run.
1) Avoid having Green Tea on an empty stomach –
Green Tea has an ample amount of catechins that are effective in weight loss. But when taken on an empty stomach these can lead to irritation and a burning feeling in the stomach.
So it is advisable not to take green tea as the first thing in the morning on an empty stomach.
2) Avoid Green Tea before going to sleep at night –
Green tea has caffeine although in a smaller amount as compared to coffee. But having a cup of green tea before going off to sleep can hamper your sleep pattern.
Caffeine is known to affect sleep quality and its onset according to studies. (25)
Inadequate sleep can adversely affect your overall health and metabolism which does not concur to a weight loss regime.
3) Take Green Tea between meals –
It is good to time your green tea cuppa between meals. They should be spaced after 1 or 2 hours of having a meal or before it.
This would ensure that you are not on an empty stomach when you have it.
Green tea is also said to inhibit iron absorption in the body. Having green tea just after a meal or during a meal may result in iron deficiency in the body. Ensuring that you take it after 1 or 2 hrs of a meal will keep a check on this.
4) Drink Green Tea before a workout session-
Before a workout session, a cup of green tea can act as your pre-workout drink.
The catechin and caffeine mixture present in the green tea induces fat oxidation during the workout and improves the overall energy expenditure of the body. (26)
Also, the small amount of caffeine in your tea would help promote alertness and athletic performance to some degree. (27)
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Best Green Tea for Weight Loss
To determine the best green tea for weight loss you must ask for the tea with the highest quantity of catechin mainly EGCG present in it.
Studies (28) have been conducted to determine the quality of green tea cultivated in Sri Lanka, South Korea, India, China and Japan which are the major producers of green tea in the world.
The highest concentration of EGCG was determined in the infusions from Japanese Sencha Tea and Green teas from Sri Lanka.
While the highest quantities of catechins were found in Korean Jeoncha followed by Japanese Green Tea samples.
How To Prepare Green Tea
To prepare a cup of green tea at home you can use a green tea bag, loose green tea leaf of green tea powder also called matcha.
With Green Tea Bags –
1) Place one tea bag in a teacup.
2) Add hot water to it. You can put a lid on the cup to prevent steam from escaping.
3) Let the bag sit in water for at least 2 to 3 minutes. More than 3 minutes might make the tea bitter in taste.
4) Remove the bag and sip your tea.
With loose Green Tea leaves –
1) Add 1 teaspoon (2 gms) of green tea leaves in the teapot or tumbler. (1 tablespoon or 5-6 gms of leaves will give a stronger tea).
2) Add a cup of hot water to it and cover with a lid.
3) After 2 to 3 minutes pour the green tea through a sieve in the cup and remove the tea leaves.
With Green Tea powder –
1) Add 1 and 1/2 teaspoon (about 2 gms) of green tea powder to a tumbler.
2) Add a cup of hot water to it and cover with a lid.
3) After 2 to 3 minutes stir the mixture and pour your tea into a cup using a sieve and enjoy it.
There are studies to prove the positive effects of green tea in weight loss process.
Green Tea catechins especially EGCG contributes to the quality of improving fat oxidation and increasing the overall energy expenditure of the body.
The Catechin Caffeine mixture in green tea has also been studied to aid in the increase of metabolism.
However, Green Tea is no substitute for regular exercise and a clean diet to effective fat loss. It must only be considered as an aid in the process.
Have you tried Green Tea for weight loss yet? If yes, do comment below with your results.