Research shows green tea boosts metabolism and fat burning, reduces belly fat and enhances aerobic capacity
by Jeff S. Volek, Ph.D., R.D.
A quick search of the popular scientific search engine Medline with the keyword "green tea" reveals more than 5,000 papers in the last 25 years. Collectively, these studies show the bioactive components in green tea to be associated with a wide range of biological effects that improve health.
Green tea contains polyphenols, with the predominant ones being the catechins which include epicatechin, epicatechin-3-gallate, epigallocatechin, and epigallocatechin-3-gallate (EGCG). Most research has focused on EGCG as the predominant active ingredient. Green tea boosts metabolism
One of the more publicized uses of green tea is for weight loss based on studies that have shown increased metabolic rate and greater use of fat. In one study, 10 healthy men with a wide range of body fat spent 24 hours in a whole room respiratory chamber to measure metabolic rate on three different occasions. During these experiments, they consumed green tea extract containing 150 mg caffeine and 270 mg EGCG (divided into 3 doses), 150 mg caffeine or a placebo. There were no effects of caffeine compared to placebo, but treatment with caffeine and green tea extract was shown to increase 24-hour metabolic rate by 4% compared to placebo. Green tea boosts fat burning
In a double-blind cross over study, obese men supplemented daily for 3 days with either placebo, 300 mg EGCG, 600 mg EGCG, 200 mg caffeine, or 300 mg EGCG/200 mg caffeine combination. On day 3 of supplementation they rested quietly for 8 hours while measures of fat oxidation were made before and after a standardized meal. The before meal fasting measures of fat oxidation were increased for the low dose EGCG (8%), high dose EGCG (15%), caffeine (26%), and combined EGCG/caffeine (35%) trials. Measures of fat oxidation after the standardized meal were increased for the low dose EGCG (33%), high dose EGCG (20%), caffeine (35%), and combined EGCG/caffeine (49%) trials. Both short-term supplementation with EGCG and caffeine alone were effective at increasing fat oxidation. Maximal fat oxidation rates were achieved with supplementation of EGCG and caffeine combined. Green tea shown to reduce belly fat
A longer-term study examined the effects of 12 weeks of drinking green tea (690 mg total catechins/day of which 136 mg was EGCG) versus placebo on weight loss and several measures of body fat in men. Men consuming the green tea had a two-fold greater weight loss (-5.3 vs -2.8 lbs) and fat loss (-3.1 vs -1.5 lbs). Compared to placebo, green tea had a dramatic four-fold greater effect on reductions in subcutaneous and visceral fat in the abdomen as measured by computed tomography imaging. Greater fat in the abdominal region is associated with higher risk for many chronic diseases.
In another study, Japanese researchers tested the effects of supplementing with green tea on weight and fat loss. Obese men and women were randomly assigned to consume daily a drink containing 625 catechins or a control beverage for 12 weeks. They were asked to make no other changes in their diet, but all subjects were required to increase daily physical activity. The catechin group lost almost 5 pounds which was more than twice the control group who lost 2 pounds. Fat loss was also greater in the catechin group (-5.2%) versus the control (-3.5%). The most noteworthy finding was that the catechin group lost significantly more fat in the abdomen (-7.7%) compared to the control (-0.3%).
In a third study, overweight men and women were fed three meals per day in a hospital kitchen for 6 weeks. Half the subjects were randomized to a control tea group and half to a green tea group. They consumed 20 ounces of tea two times per day. The green tea contained a total of 534 mg/day of catechins, compared to 162 mg/day in the control tea. There was no body fat loss in the control group, but the green tea group lost over 4 pounds of body fat. Collectively, these studies show that green tea
is an effective method for shedding fat, particularly in the mid-section. Green tea and exercise boost fat loss
Healthy men were randomly assigned to a green tea group who consumed a beverage containing 573 mg of total catechins or a placebo group. Both groups trained on a cycle for 60 minutes 3 times per week for 10 weeks. As expected aerobic capacity increased for both groups, however the green tea group showed a significantly greater utilization of fat during exercise. Thus, a combination of regular green tea extract supplementation and moderate intensity exercise training effectively increased the amount of fat burned during physical activity. Green tea enhances aerobic capacity
Maximal oxygen uptake (VO2 max) is the maximum capacity to transport and utilize oxygen. It is the hallmark of great athletes in endurance sports. To see if green tea affected aerobic capacity, healthy subjects performed two tests on a cycle ergometer to determine VO2 max – one after ingesting 135 mg of EGCG and one after placebo ingestion. Compared with placebo, EGCG supplementation significantly increased VO2 max by more than 4%. The findings are the first to indicate green tea may be a useful supplement to enhance aerobic capacity. Tea vs. supplements—dosages
If you drink green tea, there can be a great deal of variability in the content of bioactive compounds including EGCG depending on how the tea leaves were processed prior to drying, the geographic location and growing conditions, the tea type (decaffeinated, instant, etc.), and the preparation method (amount used, brew time, temperature).
Because of these “unknowns”, I think supplements that contain standardized extracts of EGCG are a good option. In fact, one study showed that supplements were better than tea. The study compared the effects of green tea (liquid), black tea (liquid), and a green tea extract (pill form) that all contained the same amount of the flavanol EGCG. Despite containing the same amount of EGCG, the absorption of total plasma flavanols into the blood after ingestion of the green tea extract supplement was far superior to the liquid teas. The green tea extract also led to higher antioxidant activity in the blood.
Another study found that ingesting supplements containing green tea catechins in a fasted state without food led to greater bioavailability compared to ingesting them with food. For weight loss, effective doses of EGCG are probably at least 270 mg a day divided into two or three doses. Some studies used higher or lower doses. For certain health conditions, you may need more. For everyday general health, you may need less. This herb is emerging as a must-have daily addition to your diet. It may provide you with fat-loss benefits, especially stubborn belly fat.