Posted on by dante

Green tea as weight loss supplement?

Green tea has been marketed as an herbal supplement for weight loss, however its potential benefits have been controversial. Green tea catechins (GTC), especially Epigallocatechin-3-gallate (EGCG), the most abundant catechins in green tea, are polyphenol compounds that have been the subject of a number of studies on the hypothesis that they may increase energy expenditure via thermogenesis effect, inhibit appetite, reduce nutrient absorption and increase fat oxidation. 

The sympathetic nervous system (SNS) plays an important role in energy expenditure regulation and lipolysis. Its activities are influenced by the concentration of norepinephrine(NE) in the body. GTC inhibits the action of COMT enzyme which degrades NE, as so does caffeine, which is also present in green tea. 

It is plausible that GTC and caffeine work synergistically in increasing energy expenditure shown in most acute and long term studies, while EGCG/GTC alone failed to elicit the same effect.
More favourable results on GTC’s effects on energy expenditure have been found in Asian population versus Caucasian, possibly due to genetic variability in enzyme activity. 

Studies on long-term effects of GTC on fat oxidation are sparse though animal trials suggest that such effects are cumulative over time. Some trials show GTC promotes lipolysis from specific fat deposits, mainly from abdomen. Effects appeared to be greatest when combined with exercise, however, available data is inconclusive regarding the relationship between GTC and exercise. Animals and humans studies on GTC as appetite inhibitor are also inconsistent.

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In vitro, GTC may reduce glucose absorption and some animal studies reported that GTC may disrupt fat digestion and absorption. 

GTC’s effect on glucose absorption and its efficacy on energy expenditure, fat oxidation and weight loss remains inconclusive. Ethnicity, doses, method of intake, potential interaction with caffeine and exercise may influence GTC’s effect.

The most recent randomised, double-blind, placebo-controlled clinical trial on EGCG’s effect on obese women failed to provide evidence of improvement in energy metabolism and lipid reduction. Supplementation did not show adverse hepatic effects either, as previously reported. 

This article was submitted as part of my Case Study.

REFERENCES:

  1. Mielgo-Ayuso J, Barrenechea L, Alcorta P, Larrarte E, Margareto J, Labayen I, 2014, ‘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’ British Journal of Nutrition vol 111 no.7, Apr, pp1263-71, doi: 10.1017/S0007114513003784.
  2. Rains TM, Agarwal S, Maki KC, 2011, ‘Antiobesity effects of green tea catechins: a mechanistic review’ Journal of Nutritional Biochemistry vol 22 no.1, Jan, pp1-7, doi: 10.1016/j.jnutbio.2010.06.006.
  3. Westerterp-Plantenga MS, 2010, ‘Green tea catechins, caffeine and body-weight regulation’ Physiology and Behaviour vol 100 no.1, Apr 26, pp42-6, doi: 10.1016/j.physbeh.2010.02.005.