Research findings about tea and weight control

At Valley Green Tea, we believe in evidence based science. Taking advantage of En Jie’s strong public health research background, we have listed and will continue to do so research findings from the Pubmed – the official database of US National library of Medicine and National Institutes of Health where most of the medicinal research findings are listed (a database used by researchers for references). We will also list research reports from other journals and sources with scientific credentials. We presents these references for our readers to draw their own conclusion in the areas of their interests. 

Being research findings in nature, the reports are scientific:

  1. The terminology used can be difficult to read for the non-researcher readers sometimes
  2. Different study findings can contradict each other at times depending on the research design, samples used, control of the confounders and other factors.
  3. Meta-analysis is a statistic method invented to overcome above weakness by pooling the research data from many studies together to find out a general direction of where the data are pointing to.
  4. Statistic jargon: 
    • statistic power - the strength of the study to represent the general population. Lowest - case study (reporting individual cases); Highest - randomised controlled trials.
    • sample - the people selected for the study
    • confounders - the factors that will bias the study results. For example, obsesity is a highly sigfinicient confounder when looking at the association between gender and diabetes. 

Green Tea

Reports of positive effect of green tea in weight control

Westerterp-Plantenga MS. Green tea catechins, caffeine and body-weight regulation. Physiol Behav. 2010 Apr 26;100(1):42-6. doi: 10.1016/j.physbeh.2010.02.005. Epub 2010 Feb 13. (https://www.ncbi.nlm.nih.gov/pubmed/20156466)

Abstract

The global prevalence of obesity has increased considerably in the last decade. Tools for obesity management including caffeine, and green tea have been proposed as strategies for weight loss and weight maintenance. These ingredients may increase energy expenditure and have been proposed to counteract the decrease in metabolic rate that is present during weight loss. Positive effects on body-weight management have been shown using green tea mixtures. Green tea, by containing both tea catechins and caffeine, may act through inhibition of catechol O-methyl-transferase, and inhibition of phosphodiesterase. Here the mechanisms may also operate synergistically. A green tea-caffeine mixture improves weight maintenance, through thermogenesis, fat oxidation, and sparing fat free mass. The sympathetic nervous system is involved in the regulation of lipolysis, and the sympathetic innervation of white adipose tissue may play an important role in the regulation of total body fat in general. Taken together, these functional ingredients have the potential to produce significant effects on metabolic targets such as thermogenesis, and fat oxidation. An ethnic or genetic effect, and habitual caffeine or green tea catechin intake may act as confounders; this remains to be revealed.

Janssens PL, Hursel R, Westerterp-Plantenga MS. Nutraceuticals for body-weight management: The role of green tea catechins. Physiol Behav. 2016 Aug 1;162:83-7. doi: 10.1016/j.physbeh.2016.01.044. Epub 2016 Feb 1. (https://www.ncbi.nlm.nih.gov/pubmed/26836279)

Abstract

Green tea catechins mixed with caffeine have been proposed as adjuvants for maintaining or enhancing energy expenditure and for increasing fat oxidation, in the context of prevention and treatment of obesity. These catechins-caffeine mixtures seem to counteract the decrease in metabolic rate that occurs during weight loss. Their effects are of particular importance during weight maintenance after weight loss. Other metabolic targets may be fat absorption and the gut microbiota composition, but these effects still need further investigation in combination with weight loss. Limitations for the effects of green tea catechins are moderating factors such as genetic predisposition related to COMT-activity, habitual caffeine intake, and ingestion combined with dietary protein. In conclusion, a mixture of green tea catechins and caffeine has a beneficial effect on body-weight management, especially by sustained energy expenditure, fat oxidation, and preservation of fat free body-mass, after energy restriction induced body-weight loss, when taking the limitations into account.

Hursel R, Viechtbauer W, Westerterp-Plantenga MS. The effects of green tea on weight loss and weight maintenance: a meta-analysis. Int J Obes (Lond). 2009 Sep;33(9):956-61. doi: 10.1038/ijo.2009.135. Epub 2009 Jul 14. (https://www.ncbi.nlm.nih.gov/pubmed/19597519)

Conclusion:

Catechins or an epigallocatechin gallate (EGCG)-caffeine mixture have a small positive effect on WL and WM. The results suggest that habitual caffeine intake and ethnicity may be moderators, as they may influence the effect of catechins.

Emad Al-Dujaili, Jon-Paul Bradley, Suzana Almoosawi & Lorna Fyfe. Effects of green tea consumption on blood pressure, total cholesterol, body weight and fat in healthy volunteers. Endocrine Abstracts (2009) 20 P470 (http://www.endocrine-abstracts.org/ea/0020/ea0020P470.htm)

Conclusion:

Our results has shown that short term consumption of commercial green tea reduces systolic and diastolic BP, fasting total cholesterol, %body fat and body weight suggesting a role for green tea in decreasing established potential cardiovascular risk factors. This study also suggests that reductions may be more pronounced in the overweight population where a significant proportion are obese and have a high risk of cardiovascular disease. Green tea consumption is cost effective, accepted by patients and has no reported side effects.

Michelle C Venables, Carl J Hulston, Hannah R Cox, and Asker E Jeukendrup. Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans. 2008 American Society for Clinical Nutrition. (http://ajcn.nutrition.org/content/87/3/778.abstract)

Conclusions:

Acute GTE ingestion can increase fat oxidation during moderate-intensity exercise and can improve insulin sensitivity and glucose tolerance in healthy young men.

Reports of no significant effect of green tea in weight control

Jurgens TM, Whelan AM, Killian L, Doucette S, Kirk S, Foy E. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database Syst Rev. 2012 Dec 12;12:CD008650. doi: 10.1002/14651858.CD008650.pub2. (https://www.ncbi.nlm.nih.gov/pubmed/23235664)

AUTHORS' CONCLUSIONS:

Green tea preparations appear to induce a small, statistically non-significant weight loss in overweight or obese adults. Because the amount of weight loss is small, it is not likely to be clinically important. Green tea had no significant effect on the maintenance of weight loss. Of those studies recording information on adverse events, only two identified an adverse event requiring hospitalisation. The remaining adverse events were judged to be mild to moderate.

Pu-erh tea

Jensen GS, Beaman JL, He Y, Guo Z, Sun H. Reduction of body fat and improved lipid profile associated with daily consumption of a Puer tea extract in a hyperlipidemic population: a randomized placebo-controlled trial. Clin Interv Aging. 2016 Mar 24;11:367-76. doi: 10.2147/CIA.S94881. eCollection 2016. (https://www.ncbi.nlm.nih.gov/pubmed/27069360

Conclusion:

The results from this clinical study showed that the daily consumption of PTE (Puer Tea Extract) was associated with significant weight loss, reduced body mass index, and an improved lipid profile.

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