Green tea (Camellia sinensis) is a healthy beverage traditionally consumed in Asian cultures. Green tea leaves are a rich source of polyphenols and other compounds with beneficial antioxidant properties. Recently, green tea has gained notoriety as a weight-loss aid, with some studies indicating that certain green tea components may have thermogenic benefits. The theory is that these thermogenic effects—including increasing fat oxidation and overall energy expenditure—could help reduce body fat and body weight.
The mechanism behind green tea’s thermogenic effects remains unclear, however. For one thing, green tea contains the compound epigallocatechin gallate (EGCG), which may account for several of the plant’s thermogenic effects; however, green tea also contains caffeine, itself a well-known thermogenic, and it is unclear whether any potential weight-loss benefits associated with green tea are due to the tea’s catechin profile, its caffeine content, or a combination of factors. Ahead, we look at what some of the most recent studies reveal about green tea for weight management.
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Fat Absorption and Body Composition
Previous clinical studies on effect of green tea supplements on fat absorption and body composition have shown mixed results. In a recent 12-week clinical trial, Pilou Janssens and colleagues from Maastricht University (Maastricht, The Netherlands) investigated the effects of green tea supplementation on fat absorption and resting energy expenditure.(1)
In the randomized placebo-controlled trial, 60 men and women aged 18–50 supplemented with nine capsules of green tea extract, or placebo, daily in divided doses. The extract provided more than 560 mg of EGCG and between 280 mg and 450 mg of caffeine per day. At the end of the study, there was no difference between green tea and the placebo on fecal energy content, fecal fat content, resting energy expenditure, or body weight or body fat, ultimately indicating that the green tea supplement had no significant effect on body composition.
1. Janssens PL et al., “Long-term green tea extract supplementation does not affect fat absorption, resting energy expenditure, and body composition in adults,” The Journal of Nutrition, vol. 145, no. 5 (May 2016): 864–870
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Fat Mass and Bone Mineral Density
In postmenopausal women, green tea supplementation has been associated with a decrease in fat mass as well as benefits to bone mineral density. It is not known, however, whether these effects are a result of green tea’s catechins or caffeine. To determine whether green tea does indeed benefit fat mass or bone mineral density, Allison Dostal and colleagues from the University of Minnesota (St. Paul, MN) conducted a sub-study in 121 overweight/obese postmenopausal women. During the study, subjects were administered a decaffeinated green tea extract providing 843 mg of EGCG, or a placebo, daily for 12 months. (This study was a sub-study of the larger Minnesota Green Tea Trial, which included 937 women.(2))
At the end of the randomized, double-blind, placebo-controlled trial, the researchers found no changes in the green tea subjects’ body mass index, total fat mass, percent body fat, or bone mineral density when compared to placebo, nor did they see changes in circulating hormones. There were, however, small improvements in tissue and gynoid fat percentage (fat distributed around the hips, breast, and thighs) in those with higher body mass index.
2. Dostal AM et al., “Long-term supplementation of green tea extract does not modify adiposity or bone mineral density in a randomized trial of overweight and obese postmenopausal women,” The Journal of Nutrition, vol. 146, no. 2 (February 2016): 256–264
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Weight Maintenance following Weight Loss
To examine whether green tea extract supplementation can help with weight maintenance following a dietary and lifestyle intervention for weight loss, Joanna Bajerska and colleagues in Poland conducted a randomized trial in 55 obese men and women with metabolic syndrome.(3) Following an eight-week weight-loss phase that involved a reduced-calorie diet and during which individuals lost an average of 7.3 kg of body weight, the subjects were randomized to two groups. One group—the treatment group—consumed rye bread containing green tea (specifically 123–158 mg of caffeine and 188–242 mg of EGCG daily) for 12 weeks. The second group was a control group who consumed non-supplemented rye bread for 12 weeks.
At the end of the study, the green tea did not provide any measurable benefits for weight maintenance versus placebo, nor did it impact HDL, triglyceride, or glucose concentrations. Green tea intake was associated with better maintenance of blood pressure levels, but overall, no significant effects were seen for weight management.
3. Bajerska J et al., “Effects of rye bread enriched with green tea extract on weight maintenance and the characteristics of metabolic syndrome following weight loss: a pilot study,” The Journal of Medicinal Food, vol. 18, no. 6 (June 2015): 698–705
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In a recent study, Spanish researchers assessed the effects of green tea EGCG on energy expenditure, body composition, and cardiometabolic risk factors in obese women.(4) In the randomized, double-blind, placebo-controlled study led by Juan Mielgo-Ayuso and colleagues, 83 obese pre-menopausal women consumed either 300 mg of EGCG or a placebo daily for 12 weeks. Metabolic and adiposity parameters were measured before and after the 12-week intervention period.
At the end of the study, the researchers found no significant changes in body weight, energy expenditure, fat metabolism, fat mass, insulin resistance, or total and LDL cholesterol levels as a result of EGCG intake compared to the placebo group. EGCG was determined to be not effective for improving energy expenditure, body fat, or weight in these women. The investigators also assessed liver function biomarkers to examine the safety of this amount of EGCG and found no adverse changes after 12 weeks.
4. Mielgo-Ayuso J. et al., “Effects of dietary supplementation with epigallocatechin-3-gallate on weight loss, energy homeostasis, cardiometabolic risk factors and liver function in obese women: randomised, double-blind, placebo-controlled clinical trial,” The British Journal of Nutrition, vol. 111, no. 7 (April 14, 2014): 1263–1271
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Jury Still Out?
Recent clinical investigations have shown a lack of effect of green tea on benefits associated with energy expenditure and weight loss. In addition to lingering questions about precisely how green tea benefits weight, recent scientific reviews have pointed to potential adverse effects associated with the use of green tea preparations—specifically, green tea supplements. A systematic review led by Gabriella Mazzanti from Sapienza University of Rome (Italy) examined reports of liver toxicity associated with the use of green tea supplements. Mazzanti’s team concluded that, while the risk of liver side effects is low, a certain risk does exist and seems to be higher with combination products and possibly with increasing doses.(5) Furthermore, while caffeine is probably safe in amounts commonly consumed on a daily basis in most healthy individuals, there have been recent concerns raised about its safety in higher doses and in certain populations.(6)
While it’s likely that certain optimized green tea preparations may perform better than others, little is confirmed regarding an effective and safe dose of green tea for weight loss. Given the inconsistent trial results as well as potential safety concerns with increasing doses of catechins and caffeine, it may be wise to take a cautious approach when it comes to supplementation.
5. Mazzanti G et al., “Hepatotoxicity of green tea: an update,” Archives of Toxicology, vol. 89, no. 8 (August 2015): 1175–1191
6. Planning Committee for a Workshop on Potential Health Hazards Associated with Consumption of Caffeine in Food and Dietary Supplements, Food and Nutrition Board, Board on Health Sciences Policy & Institute of Medicine. Caffeine in Food and Dietary Supplements: Examining Safety: Workshop Summary. (National Academies Press (US), 2014)
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