Introduction: Green tea, derived from the leaves of Camellia sinensis L., is rich in catechins, polyphenols, and caffeine. Recent interest has surged in green tea catechins (GTC) due to their potential effects on lipid metabolism and weight management. Various studies have reported beneficial outcomes of GTC on lipid metabolism, weight loss, waist circumference, abdominal body fat, and total body fat, both in the short and long term. However, the literature presents conflicting evidence, with the inconsistency stemming from variations in study designs and GTC bioavailability. Moreover, the precise mechanism by which GTC increases fat oxidation in the human body remains unclear, necessitating further research to better understand its role in lipid metabolism.
Methods: A comprehensive search was conducted on PubMed, ResearchGate, and Embase to identify intervention studies that examined the impact of GTC on lipid metabolism and weight management, published up to October 2020.
Results: The findings are inconclusive and inconsistent, with some evidence suggesting that the combination of GTC (specifically epigallocatechin gallate, EGCG) and caffeine may reduce cholesterol and triglyceride absorption while inhibiting alpha-tocopherol uptake. Additionally, compared to caffeine alone, the combination of GTC and caffeine has been shown to increase fat oxidation by 20% within 24 hours. The synergistic effect of GTC and caffeine appears to involve energy expenditure, thermogenesis, and lipolysis, mediated by the disruption of sympathetic nervous system (SNS) activity. GTC inhibits catechol O-methyltransferase (COMT), the enzyme responsible for norepinephrine degradation, thereby prolonging norepinephrine's activity, reducing glucose uptake, and enhancing lipolysis and thermogenesis. Meanwhile, caffeine acts as a phosphodiesterase antagonist, preventing the degradation of cyclic adenosine monophosphate (cAMP) and further promoting fat breakdown.
Conclusion: Current evidence is insufficient to draw definitive conclusions about the use of green tea catechins or extracts for weight management. Inconsistencies in findings may be attributed to methodological challenges in the studies. A well-designed, high-quality clinical trial, utilizing GTC alone or in combination with other weight management strategies, is needed to provide clearer insights.
Keywords
Green Tea; Green Tea Catechins; Green Tea Extract; Caffeine; Lipid Metabolism; Weight Management