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December 2008
Green Tea and Obesity: Part 2
In October's EBM Tip column, we used our search for the effects of green tea on obesity as a comparison for Google and PubMed searching. I concluded that our PubMed results were more complete and trustworthy for EBM searching. Did you agree? This month, let's look at the results of those searches.
We have five randomized control trials (RCT) that look at green tea or a green tea extract and obesity or an obesity-related condition in children, and one prospective study:
- Hsu CH, Tsai TH, Kao YH, Hwang KC, Tseng TY, Chou P. Effect of green tea extract on obese women. Clin Nutr. 2008 Jun;27(3):363-70.
- Westerterp-Plantenga MS, Lejeune MP, Kovacs EM. Body weight loss and weight maintenance in relation to habitual caffeine intake and green tea supplementation. Obes Res. 2005 Jul; 13(7):1195-204.
- Matsuyama T, Tanaka Y, Kamimaki I, Nagao T, Tokimitsu I. Catechin safely improved higher levels of fatness, blood pressure, and cholesterol in children. Obesity (Silver Spring). 2008 Jun;16(6):1338-48.
- Rudelle S, Ferruzzi MG, Cristiani I, Moulin J, Macé K, Acheson KJ, Tappy L. Effect of a thermogenic beverage on 24-hour energy metabolism in humans. Obesity (Silver Spring). 2007 Feb;15(2):349-55.
- Kovacs EM, Lejeune MP, Nijs I, Westerterp-Plantenga MS. Effects of green tea on weight maintenance after body-weight loss. Br J Nutr. 2004 Mar;91(3):431-7.
- Sugimori H, Yoshida K, Izuno T, Miyakawa M, Suka M, Sekine M, Yamagami T, Kagamimori S. Analysis of factors that influence body mass index from ages 3 to 6 years: A study based on the Toyama cohort study. Pediatr Int. 2004 Jun;46(3):302-10.
Here is a comparison of the RCTs:
| Study | Population | Intervention | Blinded | Outcomes | Comments |
| Hsu et al. Clin Nutr. 2008 Jun;27(3):363-70. |
100 obese women aged 16-60; computer randomized |
Capsule 400 mg green tea extract 3 times a day for 12 weeks vs. placebo (cellulose capsule) |
* Subjects
* Research assistant who distributed capsules |
* Primary: After 12 weeks, no statistically significant reduction in % of body weight (BW), BMI, or waiste circumference (WC)
* Secondary: statistically significant reduction in LDL -cholesterol and triglyceride; increase in HDL cholesterol |
* No intention to treat analysis
* Study was adequately powered
* 12 week follow-up may be inadequate
* Route of administration might change impact |
Westerterp-Plantenga et al.
Obes Res. 2005 Jul; 13(7):1195-204. |
76 male and female obese or moderately overweight, aged 18-60; stratified by low or high habitual caffeine consumptions, and randomized within those groups. |
Green tea (epigallocatechin gallate)-caffeine mixed with vegetable oil, 2 capsules before each meal vs. placebo (vegetable oil alone) |
Study stated as double blinded; patients given similar capsules. |
* Neither BW nor satiety differed between the two treatment groups, but were higher in high-caffeine group.
* Weight regain, insulin and tracylglycerol were smaller in low-caffeine treatment group |
*Subgroups with small n(19) were analyzed
* Small statistical differences may not be clinically significant. |
| Matsuyama et al. Obesity (Silver Spring). 2008 Jun;16(6):1338-48. |
42 subjects: obese male and female children aged 6 - 16; randomization stated but not explained. |
A brew of green tea and added green tea extract (catechin), given once a day in a 340 ml can with 576mg/can vs. placebo can of 75mg/can to make similar in taste |
* Patients
* Study states that it was double blinded, but no information is given about other blindings. |
* No effect for BMI, body-fat ratio, blood pressure or hip circumference.
* Slight but statistically significant reduction in WC at 24 weeks. |
* Severe dietary restriction for both groups during the study period.
* No intention to treat analysis; initial dropouts excluded from analysis |
| Rudelle et al. Obesity (Silver Spring). 2007 Feb;15(2):349-55. |
32 healthy male and females aged 18 to 35 years with a BMI between 20 and 25. |
Cold beverage of green tea extract with daily total of 540 catechin 300 mg caffeine and 633 mg calcium vs. similarly colored placebo beverage, each taken 3 times per day |
Test beverage made indistinguishable to both investigators and subjects |
* 24-hour fact oxidation was the primary outcome; there was not a statistically significant difference.
* Carbohydrate oxidation was not significantly greater.
* Total energy expenditure was greater in the green tea group, by @ 100 calories per day. |
* Randomization stated but not explained.
* One subject dropped from analysis
* Caffeine may have been a factor in group differences |
| Kovacs et al. Br J Nutr. 2004 Mar;91(3):431-7 |
120 healthy male and female subjects, with BMI of 25-35, randomized to an intensive group (80) or an extensive group (40) |
104 mg caffeine + 573 mg catechin per day in 6 capsules taken 2 per meal vs. placebo capsule. 51 subject received green tea and 53 received placebo; randomization stated. |
Administration of the capsules was double blinded |
During the weight-maintenance period, no differences between green tea and placebo group in weight-loss retention, metabolic and blood parameters, WC, body mass or BMI. |
* Study began with a 4-week very-low energy diet for all subjects
* Higher caffeine intake among green tea group
* Intention to treat analysis not clear |
All of these studies focused on more than obesity. They also measured many factors thought to contribute to diabetes, hypertension and other obesity-related diseases. Some of these outcomes did reach statistical significance. The diet and exercise routines of the groups during the study period varied, and different formulations of green tea were used in each study. Only one of these RCTs enrolled only children, and that study had a very small n. Hence, there is need for further study, particularly in children.
So, let's say we were asked to be on the Oprah Winfrey show to talk about the effectiveness of green tea for weight reduction? What do we know?
- None of the studies saw a statistically significant change in weight loss, although one showed a slight decrease in waist circumference.
- There were some trends and other factors that were beneficial, such as the increase in HDL cholesterol and decrease in LDL cholesterol.
- None of these studies showed adverse effects.
- The purity and dosage of herbal supplements is not consistent.
That is what the evidence tells us. Now, what do you say to Oprah, and to your patients when they ask you?
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Laura Cousineau, MLS
MUSC Library
Dept. of Pediatrics EBM Faculty |
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