Green tea is a beverage created by lightly steaming the leaves of Camellia sinensis, the tea plant. Unlike black tea, green tea leaves are not fermented during processing, giving them high levels of substances that have been found to confer a broad range of healthful benefits, from guarding against cancer to preventing obesity. Green tea has been known to the Asian world since its discovery by Shennong, the emperor of China some 5000 years ago. The ‘Divine Farmer,’ as he was called, personally tested hundreds of herbs to discover their properties, laying the groundwork for Chinese herbal medicine.
In the 1600’s, a Chinese pharmacist named Wang Ang noted that consumption of tea over a prolonged period reduces fat. However, it wasn’t until 1995 that Western medicine began conducting clinical trials to test green tea’s potential to prevent obesity.
Obesity is now considered one of the greatest health challenges facing the modern world. One in four Americans is obese and the related medical costs in the U.S. are over $100 billion annually. We are fat because we live a very sedentary lifestyle, we eat too much, and the food we consume lacks necessary nutrients. A recent report released by the Organization for Economic Cooperation and Development predicts that by 2020 75% of Americans will be obese. A negative energy balance is a prerequisite for weight loss, either by reducing the quantity of caloric intake or increasing the amount of energy expended. (back to top)
Camilla sinensis contains flavonoids called catechins, which are central to green tea’s physiological effects.
An epidemiological study conducted in Taiwan in 2003 observed the effects of habitual tea consumption on body fat distribution, surveying 1103 adults. The conclusion was that people who had consumed tea at least once weekly for a duration of ten years or more carried 20% less body fat – and had slimmer waistlines – than people who did not consume tea regularly.
A human intervention study was conducted in 2005 on 240 obese Japanese men. The subjects were administered a daily dose of catechin-enriched green tea for a duration of 12 weeks. As a result, the subjects showed a significant decrease in visceral fat, waist circumference, body weight and LDL cholesterol. Other studies have replicated the results. In all of these studies, the subjects did not alter their customary level of physical activity, nor their usual dietary intake.
In The Netherlands, a longitudinal cohort study processed data on 4280 adults, collected over a 14-year period. An inverse relationship between catechin consumption and body mass index (BMI) was discovered: the more catechins consumed, the lower the BMI.
These findings showed that consuming green tea can promote weight loss. (back to top)
A person’s ability to store fat is determined by the quantity and size of his/hers fat cells called adipocytes. Fewer fat cells mean less fat storage potential. For adipocytes to be created, cells known as pre-adipocytes must undergo a process called adipogenesis.
Fatty tissue formation depends on a constant regeneration of adipocytes because fat cells are constantly dying and need to be replaced. Cell studies have shown that adipogenesis is disrupted by the daily consumption of green tea, preventing the genesis of new fat cells and the formation of fatty, or adipose, tissue. (back to top)
REE or Resting Energy Expenditure is the number of calories the body burns even while sleeping. This is also called the BMR or basal metabolic rate. A portion of available caloric energy is burned during rest to maintain a constant body temperature in a process called thermogenesis. Green tea has been found to be a thermogenic food, because it causes the body to release more heat and burn more calories while in a resting state.
|Lift for Life BMR Calculator|
The objective of a 1999 interventional study in France was to determine whether REE could be increased in human subjects by administering green tea extract. Three separate tests were conducted on 10 healthy men. For the first test, a capsule containing green tea extract was given with each meal. The capsule contained caffeine for the second test and a placebo for the third. The findings showed that green tea extract increased REE by 4%. The increase in REE from caffeine or the placebo was significantly lower.
A similar study in Lausanne, Switzerland tested the effects of a green tea beverage administered 3 times daily to 31 female and male subjects. At the end of three days, REE was discovered to have increased by between 4 and 8%. This figure translates into an additional 100 calories burned per day while the body is at rest. Well, this may not sound like a lot, until you realize that it takes only 50 extra calories a day to gain 5lb a year. The findings showed that green tea promotes weight loss by increasing the basal metabolic rate. (back to top)
According to the Harris-Benedict and the Mifflin-St Jeor equations, the more body weight there is, the greater the basal metabolic rate (BMR). As a person loses weight, the BMR goes down. This is the cause of the weight loss plateau experienced by dieters after they have shed pounds initially. A lower BMR makes it difficult to maintain weight loss. Studies have shown that increasing BMR through the daily ingestion of green tea facilitates weight maintenance. (back to top)
Lipids (fats) must undergo two transformations before being absorbed by the body:
1. Conversion to emulsion. The intestines cannot absorb fat-soluble material such as lipids. In order for fats to become water-soluble, they require emulsification through the action of bile salts. These salts, which are released by the gallbladder, form a water-soluble sphere called “micelle” that encloses lipids, allowing them to be absorbed into the bloodstream.
2. Digestion by lipases. Lipids must be broken down in the stomach and small intestine by enzymes called lipases.
In both in vitro and animal models, the catechins in green tea have been found to decrease lipid absorption. EGCG is the most powerful and abundant catechin found in green tea. It has been shown to inhibit the creation of micelles and also to block both stomach lipase and pancreatic lipase. The unabsorbed fats are then excreted from the body. (back to top)
Protein, carbohydrates and fats are the three major macronutrients that constitute food. Upon consumption, the body breaks down the macronutrients into assimilable components. Proteins split into amino acids; carbohydrates become sugar; and fats take the form of fatty acids. Once these components are absorbed, the body uses them for a number of biological processes. Leftover components are sent to the fat cells for storage.
Adipocytes (fat cells) can only store fat, so all those leftover components must first be turned into fat before being put away -- this is achieved by a process known as lipogenesis, which is carried out by lipogenic enzymes. Green tea hinders this process, thereby reducing the amount of fat sent to storage. (back to top)
The ancients knew that green tea confers many health benefits and assists in weight loss. Now these results have been confirmed by scientific studies. Perhaps the most significant finding is that the catechins in green tea raise the REE, or resting energy expenditure. The implication of this discovery is that weight loss for most Americans can be achieved without drastically altering their lifestyles.
Approximately 90% of the American population consumes an average of 25 calories per day beyond their energy needs, resulting in a weight gain of 2.2 pounds per year. Since regular green tea consumption can burn an extra 100 calories per day by raising the basal metabolic rate, this would imply a net weight loss even before reduction of caloric intake or increase in exercise.
Could the addition of green tea to the diet make a realistic public health goal in the fight against obesity? A 2010 report from the University of Connecticut that reviewed and analyzed all previous studies on the effect of administration of green tea catechins (GTCs) on various anthropometric measures found that, indeed, green tea can reduce body weight and waist circumference. However, this weight loss effect of green tea has a modest clinical significance. The study concluded: “Current data do not suggest that GTCs alone positively alter anthropometric measurements.” Therefore, proper diet and regular exercise are irreplaceable when body fat reduction is the goal. (back to top)
Matthew Papaconstantinou, PhD, uses his educational background in obesity and related diseases to present scientific findings in a format that is easily understood. He has a broad range of interests, which include strategies for weight management, diets and weight loss programs. In his blog he features clinically studied weight loss programs and offers a Medifast coupon and a promotional discount for Weight Watchers.
1. Effect of green tea catechins with or without caffeine on anthropometric measures: a systematic review and meta-analysis. Phung OJ, Baker WL, Matthews LJ, Lanosa M, Thorne A, Coleman CI. Am J Clin Nutr. 2010 Jan;91(1):73-81.
2. Green tea catechins, caffeine and body-weight regulation.Westerterp-Plantenga MS. Physiol Behav. 2010 Apr 26;100(1):42-6.
3. Proposed mechanisms of (-)-epigallocatechin-3-gallate for anti-obesity. Moon HS, Lee HG, Choi YJ, Kim TG, Cho CS. Chem Biol Interact. 2007;167:85–98.
4. The potential role of green tea catechins in the prevention of the metabolic syndrome: a review. Thielecke F, Boschmann M. Phytochemistry. 2009;70:11–24.
5. Effect of EGCG on lipid absorption and plasma lipid levels in rats. Raederstorff, D. G., Schlachter, M. F., Elste, V., Weber, P. J. Nutr. Biochem. 2003, 14, 326–332.
6. Tea catechins decrease micellar solubility and intestinal absorption of cholesterol in rats. Ikeda I, Imasato Y, Sasaki E, et al. Biochim Biophys Acta 1992;1127:141– 6.