Humans have consumed green tea for thousands of years; it’s health and spiritual benefits are numerous. It’s no wonder that Green Tea Extract (GTE) was developed in order to magnify the benefits of this wonderful plant. Camellia sinensis is the plant from which all green tea is made. While this superfood’s antioxidants and general wellness properties are well known, it is also used to help aid in weight control and fat loss. GTE is now featured in many fat burning, sports nutrition supplements and is becoming more popular for those interested in improving their body composition (ratio of fat to lean muscle). Let’s review the benefits of GTE, the side effects, and if a green tea supplement is right for you.
Green tea is rich in natural phenols and polyphenols, compounds found naturally in plants. Tea has extremely high concentrations of flavonoids, a type of natural phenols.  Of these flavonoids, the most important to those interested in the health benefits are catechins. Besides their incredible antioxidative properties, catechins also have a thermogenic effect that promotes weight and fat loss.  
GTE is essentially extremely high concentrates of green tea polyphenols (GTPs). The benefits of green tea can be enhanced in capsule or pill form due to the higher concentrations of nutrients. Most servings sizes of GTE equate to about 4-6 cups of tea. There are a couple of different ways in which these concentrates are made from the tea leaves, but the common form of extract for supplementation is dry extract (powder), which is used for pills, tablets and capsules. 
One of the side effects of high intensity training is cell damage, which is caused by free radicals naturally released during exercise. By supplementing with antioxidants, you can protect yourself from the potential muscle, joint and tendon inflammation as well as damage caused by free radicals and consequently accelerate the healing process. For this reason, various antioxidants are included in sports nutrition supplements. Green tea is an amazing source of antioxidants, protecting the body from harmful free radicals. To understand how GTE affects the body, we must understand what its most important component is: Catechins.
Catechins are a sub-class of flavanoids. These are antioxidant molecules that may potentially help in reducing risks of Alzheimer’s, cancer and cardiovascular disease.  The four important catechins in green tea are epigallocatechin gallate(EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC). The highest concentration of these catechins is EGCG, which is the most widely researched catechin found in green tea.
Catechins are helpful in boosting your metabolism and consequently fat loss due to their relations ship with an enzyme called catechol-O-methyltranferase (COMT). COMT breaks down Norepinephrine, a hormone in the human body that helps regulate metabolism. A higher concentration of norepinephrine means a faster metabolism. Catechins help inhibit COMT which therefore helps keep your metabolism higher.  There have also been studies performed on the positive correlation between caffeine and catechins, which enhances the metabolic benefits. A combination of caffeine and catechins increases 24-hour energy expenditure and also increases fat-oxidation. 
Studies have shown that a combination of GTE and moderate exercise increases fat oxidation and glucose tolerance.  In experiments where both test subjects supplementing GTE and placebo test subjects participated in moderate exercise, the subjects supplementing GTE showed greater loss of body weight, abdominal fat, subcutaneous abdominal fat, and fasting serum triglycerides. Similar studies also showed lower levels of low-density lipoproteins (LDL cholesterol) and lower systolic blood pressure. 
There are various schools of thought on the effective dosage of GTE. Most studies involve daily dosages of 300mg to 700mg. As GTE contains caffeine, it’s important to start on the lower end of the spectrum and assess your tolerance. With all supplementation, read labels carefully and consult with a physician before consumption.
Though considered safe for most healthy adults, due to the caffeine content of green tea, side effects can include those associated with caffeine sensitivity. There is typically 20-40mg of caffeine per 8oz cup of green tea. For reference, an 8oz cup of coffee has around 90-110mg. GTE servings can range from around 80-150mg of caffeine so make sure to check the labels. Decaffeinated GTE is available and many supplements regulate how much caffeine is in each capsule.
With all of its antioxidants and disease fighting properties, green tea extract's health benefits extend beyond getting you shredded for beach season. When combined with proper nutrition and exercise, it can help speed up the fat burning process. However, it’s important to note that it will not cut your body fat levels all by itself. You must change your long term lifestyle (proper nutrition and exercise) to see long term results.