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Green Makes You Lean?
The Truth about Green Tea and Weight Loss
Dr. David Schlundt
September 20, 2006
the obesity epidemic in the
What makes green tea different from regular tea?
Green tea is often publicized in the media as a delicious way to burn fat and lose weight. However, black tea is also naturally calorie-free, so this question often arises. Studies comparing the effects of regular caffeinated teas on metabolism and those of green tea have purportedly found that subjects’ rates of fat metabolism are significantly increased in those drinking green tea extract (http://www.lipton.com/tea_health/appearance/index.asp).
Green tea, black tea, and oolong tea all originate from the Camellia sinensis plant, an ancient evergreen shrub. However, the leaves collected for the production of black tea are fermented after plucking. The leaves destined for green tea production are simply steamed, preserving more of the natural chemical compounds present in the leaves ( ). These compounds, called polyphenols and, in particular, flavonoids, yield most of the potential health benefits of green tea due to their antioxidant properties (Nagle, Ferreira, & Zhou, 2006). The most biologically active of these polyphenol compounds is thought to be epigallocatechin gallate (EGCG), which cannot be found in comparable quantities in any other functional food source (Diepvens, Westerterp, and Westerterp-Plantenga, 2006). Traditional Chinese medicine has recommended green tea as an aid for a number of bodily ailments for centuries, and recent studies have indicated that green tea can play a role in a successful body weight control regimen (Cabrera, Artacho, and Giménez, 2006).
Through what mechanisms is green tea supposed to work?
Green tea is thought to have numerous medicinal properties, which contribute to its antioxidant and antiaging benefits, its supposed ability to reduce blood cholesterol levels and improve cardiovascular health (Cooper, Morré, & Morré, 2005), its anticarcinogenic potential, its benefits in oral and bone health, and its alleged role in glucose tolerance and weight control (Cabrera, Artacho, and Giménez, 2006). The high concentrations of catechin polyphenols present in green tea provide the foundation for the beverage’s positive influences on body composition (Dulloo, et al., 1999). These compounds enhance levels of oxidative fat metabolism and thermogenesis, the process by which heat is created in the body through the burning of fat and other fuels.
levels of polyphenols, such as epigallocatechin
gallate, in green tea are thought to interfere with
the sympathetic nervous system’s use of norepinephrine,
a stress hormone that releases stored energy from fat, thereby increasing the
rate of metabolism (Dulloo, et al., 1999). The
processes of thermogenesis and fat oxidation are
largely controlled by the sympatho-adrenal system.
The flavonoids and other chemical compounds in green
tea have been implicated in the inhibition of the enzyme catechol
O-methyl-transferase (COMT), which is responsible for
degrading norepinephrine (
What claims are being made about the potential benefits of green tea in weight loss?
Thus, due to green tea’s apparent dual mechanism for body weight control, a number of products containing green tea or green tea extract have been introduced into the market accompanied by claims about their “fat-burning power,” particularly on the Internet. One particular site touts the power of green tea with its slogan, “Sip Yourself Slim,” and states that “green tea… contains a unique antioxidant so powerful that it works as well as any diet pill” (http://1800patches.com/telite/index2.html?CFID=15845207&CFTOKEN=63739987). Although a great deal of research is being conducted in this area, this claim is unfounded at this point in time. However, this website consistently refers to green tea as being a “weight loss miracle” and claims that their product, Te-Lite ® instant beverage packets, will help an individual lose weight with “no diet overhaul needed.”
Another website specifically makes a statement that has already been elucidated as untrue. This website, http://www.vitaminstohealth.com/green-tea-weight-loss.html, prominently displays the following testimonial, “Green tea does contain caffeine, but you can get herbal preparations without the caffeine. The good news for people who don't like caffeine, is that it is the catchetins (sic) that produce green tea's thermogenesis effects, not the caffeine.” However, Westerterp-Plantenga, Lejeune, and Kovacs (2005) concluded that the combination of green tea and caffeine yielded the greatest thermogenic and fat-metabolizing effects, and, therefore, the greatest overall impact on body weight maintenance.
Additionally, the media presents explicit claims about the amount of calories green tea can burn on the World Wide Web. Not only are these claims unsubstantiated by scientific evidence, they are inherently inaccurate because metabolic rates vary greatly across the population, especially in their target audience—dieters. Green tea intake is purported to burn 78 calories per day, or 28,000 calories per year, simply by boosting metabolism on a website for Anne Collins’ Weight Loss program ().
A number of beverage companies, including Celestial Seasonings ® and Lipton ®, dedicate significant portions of their websites to the supposed health benefits of drinking green tea, particularly those related to weight control. The Celestial Seasonings website invites consumers to “view [their] full line of green teas and choose from one of [their] many satisfying green tea flavors.” The site passively refers to recent studies that support green tea’s role in increasing metabolism and controlling weight, while also noting that regular tea drinkers have lower body fat percentages than the rest of their non-tea-drinking cohort (http://www.celestialseasonings.com/research/abouttea/weightmanagement.php). Lipton’s website admits that the studies they present about green tea and weight loss are not conclusive, but maintains that tea is an “ideal choice for a weight control plan” (http://www.lipton.com/tea_health/appearance/index.asp). Consumers must carefully examine the sources they encounter on the Internet and always consider that every website has a purpose, whether it is to sell a potentially worthless “miracle” supplement for weight loss or to properly inform the public about scientific findings impacting their health.
Is there scientific evidence to support these claims?
A review of the scientific literature yields promising results in regard to green tea’s potential impact on effective weight management; however, the use of green tea as a miracle cure for obesity is not fully justified by the research on the subject.
One study by Dulloo et al. (1999) investigated whether green tea extract could be linked to an overall increase in energy expenditure and rate of fat metabolism in humans. Notably, the sample in this study consisted of only ten healthy men. The subjects were kept in a respiratory chamber for observation and measurement and were randomly assigned to one of three treatments: a green tea extract tablet containing caffeine and EGCG, caffeine alone, or a placebo of inert cellulose, each taken three times a day at mealtimes. The subjects’ response to treatment was measured in terms of energy expenditure in the morning and evening. The rate of energy expenditure increased in six of the ten subjects after exposure to the green tea extract treatment. The authors of this study found this result to be significant; however, these results surpassed those in the placebo group by only 3.5%. This observed effect on metabolic rate translates into an increase in 24-hour energy expenditure of only 4%, and, notably, there was no significant difference in nighttime energy expenditure between the three treatment groups.
Another group of researchers assessed the potential impact of the intake of green tea extract in combination with a calorie-restricted diet on resting energy expenditure (Diepvens et al., 2005). The sample size in this study was much greater, as treatments were applied to forty-six overweight women. The study lasted eighty-seven days, during which subjects were fed a meal-replacement diet. This particular diet plan consisted of Slim-Fast ® meal replacements for breakfast and lunch, followed by a sensible dinner and snacks. Either a green tea capsule or a maltodextrin tablet (as a placebo) was administered at each meal as an experimental treatment or control, respectively. Body weight and composition were measured on days 4, 32, and 87 of the study. While a significant weight reduction was observed during the low-energy diet (LED) phase of the study, the decrease in body weight was not significantly different between the two groups. Therefore, the weight loss accomplished in the study can be attributed to the calorie-restricted diet, but not to the ingestion of green tea extract. In fact, researchers observed a surprising effect in the green tea treatment group. Subjects given the green tea treatment actually exhibited an increased appetite and food consumption compared to the placebo group. The researchers concluded that green tea extract did not generate any additional weight reduction benefits as a part of a low-calorie diet, and that green tea extract did not produce a stimulatory effect on fat oxidation or thermogenesis.
An important contrast between these two studies is that Dulloo’s small sample included ten healthy young men, who were self-described as “lean” to “mildly overweight.” However, the subjects in Diepvens’ study were clinically overweight and middle-aged women, who are more likely the target audience of the marketing of green tea products. The second study was conducted specifically in a weight-loss state, involving dietary restriction, whereas the first study should be considered a weight-maintenance program because the subjects were not clinically overweight and were not fed a calorie-restricted diet.
Will green tea work to help you lose weight?
Green tea is certainly a good alternative beverage choice available to dieters since it is all-natural and calorie-free; however, the use of supplements containing green tea extract will not serve as a panacea for one’s weight loss woes. Instead, the best and only guaranteed method of weight reduction is a well-managed diet and exercise plan. Any claim that drinking four or more cups of green tea each day will produce dramatic effects on metabolic rate is largely unfounded, but, obviously, drinking unprocessed green tea is a much healthier decision than taking another of the hyped fat-burning dietary supplements on the market, which may contain dangerous compounds like ephedrine. The scientific evidence leads more closely to the conclusion that green tea can be beneficial in a weight-maintenance plan, but not in one intended for obesity management or excessive weight loss.
Cabrera C., Artacho, R., & Giménez, R. (2006).Beneficial effects of green tea—A
review. Journal of the
Cooper, R., Morré, D.J., & Morré, D.M. (2005). Medicinal benefits of green tea: Part I. Review of noncancer health benefits. Journal of Alternative and Complementary Medicine, 11(3), 521-528.
Diepvens, K., Kovacs, E.M, Nijs, I.M., Vogels, N., & Westerterp-Plantenga, M.S. (2005) Effect of green tea on resting energy expenditure and substrate oxidation during
weight loss in overweight females. British Journal of Nutrition, 94(6), 1026-34.
Diepvens, K., Westerterp, K.R., and Westerterp-Plantenga, M.S. (2006). Obesity and thermogenesis related to the consumption of caffeine, ephedrine, capsaicin and green tea. Journal of Regulatory, Integrative, and Comparative Physiology, Published electronically ahead of print.
Dulloo, A.G., Duret, C., Rohrer, D., Girardier, L., Mensi, N., Fathi, M., Chantre, P. and Vandermander, J. (1999). Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. American Journal of Clinical Nutrition, 70(6), 1040-1045.
Nagle, D.G., Ferreira, D., & Zhou, Y.D. (2006). Epigallocatechin-3-gallate (EGCG): Chemical and biomedical perspectives. Phytochemistry, 67(17), 1849-1855.
Westerterp-Plantenga, M.S., Lejeune, M.P, & Kovacs, E.M. (2005). Body weight loss and weight maintenance in relation to habitual caffeine intake and green tea supplementation. Obesity Research, 13, 1195-1204.
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