Green tea is a rich source of polyphenol catechins. Epigallocatechin gallate (EGCG) is the most active form of the catechins responsible for green tea’s antioxidant, anti-inflammatory, and metabolic effects. Green tea also contains caffeine, which appears to act synergistically with EGCG to assist metabolism. A recent meta-analysis of all human green tea weight loss studies1 found that green tea containing caffeine works best, and produces a statistically significant reduction in body weight, body mass index, and waistline.
In a randomized placebo controlled trial moderately overweight adults consumed 1,900 mgs of green tea catechins per day for 90 days. The green tea also contained 400 mg of caffeine. At the end of the study the people in the green tea group lost 2.64 pounds on average, and ¾ inch from their waistline and also reduced body mass index—not bad considering that no dietary or exercise changes were part of the study.
A 12-week randomized controlled trial3 with 60 obese adults was performed in a hospital setting with all 60 participants placed on a diet that included three meals per day. All the food was prepared for the participants. Half the group received green tea. Those in the green tea group lost significantly more weight—24 pounds—over the 12 week period. The researchers demonstrated that weight loss occurred by green tea increasing energy expenditure and fat oxidation.
Another 12-week randomized controlled trial4 with green tea and obese adults produced little weight loss (less than 1 pound). There was no dietary intervention and the dose of green tea catechins was relatively low (458 mg per day). However, even this modest intake of green tea catechins did produce statistically significant reduction in LDL cholesterol and triglycerides while raising the protective HDL cholesterol, and adiponectin, which prevents insulin resistance. Even though weight was not improved on this dose of green tea it did produce a variety of important metabolic changes that are associated with reduced risk for diabetes and heart disease.
Consumption of 582 mg of green tea catechins per day for 12 weeks in type 2 diabetic patients5, compared to a control group of diabetic patients, enabled a statistically significant reduction in their waistline (abdominal fat). Importantly, green tea catechins promoted a restored insulin production by the pancreas. Catechins caused a significant increase in adiponectin, the important hormone signal coming from fat that improves insulin resistance. The combination of diabetic medication and green tea produced a statistically significant reduction in hemoglobin A1C. These results indicate that even modest intake of green tea catechins improves blood sugar control in type 2 diabetic patients. When blood sugar control is being improved in conjunction with a trend of weight loss, health is being restored.
Consumption of 576 mg green tea catechins per day for 24 weeks in obese children6 found that those who were the most obese had a statistically significant reduction in waist circumference, blood pressure, and LDL cholesterol.
A study published in 2010 in the American Journal of Clinical Nutrition7 showed that a combination of green tea, resveratrol, vitamin E, vitamin C, omega-3 fatty acids, and tomato extract given to overweight men for five weeks raised their adiponectin level by seven percent. The researchers documented numerous favorable metabolic changes indicating: modulated inflammation within white adipose tissue, improved endothelial function of arteries, improved antioxidant function, and increased fat burning by the liver.
It is well-known that being overweight or obese is associated with increased inflammation, both within white adipose tissue and around your body. One way to help calm inflammation is through the function of specialized regulatory T cells8 that initiate signals that are anti-inflammatory. A recent study in the British Journal of Nutrition9 found that obese humans have fewer of these important regulatory T cells than normal weight people and the T cells they did have were less active in terms of quenching inflammation. The researchers went on to expose the regulatory T cells of the obese people to ECGC and found that the T cells woke up and started producing anti-inflammatory signals and were then able to cause the reduction in NF-kappaB, the primary inflammatory gene signal. Researchers also showed that ECGC increased anti-inflammatory activation in the regulatory T cells of the normal weight people in their study.
Further insights into the molecular mechanisms of green tea come from a variety of recent animal and cell studies. Studies with fat cells show that green tea catechins turn on gene signals that produce adiponectin10. Adequate adiponectin production is required to prevent insulin resistance and type 2 diabetes. Green tea has been shown to blunt the effect of insulin on baby fat cells11, helping prevent them from turning into mature fat storing fat cells. Another study shows that green tea prevents the accumulation of fat12 inside fat cells. While yet another study shows that green tea turns on genes within fat cells that dispose of calories as heat13 (a helpful way to get rid of excess). Collectively, green tea induces multiple favorable effects on white adipose tissue, which are supportive of weight loss.
Leptin is the primary hormone coming from white adipose tissue that regulates weight gain. Too much leptin in the blood causes leptin resistance, a problem that sets into motion all manner of poor metabolic health. A recent animal study showed that green tea decreased total cholesterol, LDL cholesterol, and triglycerides while also lowering the levels of leptin14 in the blood.
Transgenic mice—mice that make no leptin—(ob/ob) experience unrelenting appetite, obesity, and fat accumulation in all the wrong places, such as the liver. In this extreme model of malfunction green tea was able to prevent fat from accumulating in the liver15. This finding is significant since fat accumulation in the human liver is a key marker that metabolic health is in big trouble.
In another transgenic mouse, this one programmed to die more quickly, it was found that green tea in combination with exercise16 extended the mouse’s health and life. The green tea enabled better use of oxygen by muscles, improved antioxidant function within muscles, and increased the rate of fat burning by muscles.
A recent study also showed green tea helps build bone17. Green tea catechins significantly boosted the activity of bone building cells known as osteoblasts while reducing the activity of the osteoclasts that take down bone. A significant reduction of the primary inflammatory gene signal, NF-kappaB, was associated with these positive findings. Not only is this good news as yet another bone helping nutrient, but new science is also showing that positive bone health and proper metabolism are highly linked.
Green tea is one of the most widely consumed beverages in the world. Dietary supplements that concentrate the active components of green tea offer consumers a novel tool to assist multiple aspects of metabolism. Combining green tea with appropriate diet and exercise yields the best results, which is true for any dietary supplement. Green tea is synergistic with many other nutrients and is a worthy candidate for any person seeking to manage his or her weight.