Green tea, black tea, and epigallocatechin modify body composition, improve glucose tolerance, and differentially alter metabolic gene expression in rats fed a high-fat diet
Introduction
Tea is the second most widely consumed beverage in the world following water. The most commonly consumed teas are black, green, and oolong which are all derived from the plant Camellia sinensis, a member of the Theaceae family. Approximately 3.0 million metric tons of dried tea is produced annually, 20% of which is green tea (GT), 2% is oolong, and the remainder is black tea (BT) [1]. GT and oolong tea are predominantly consumed in Asian countries, whereas BT is widely consumed in India and Western countries.
Differences in leaf oxidation during processing yield the different types and chemical characteristics unique to each tea. Chemical compounds called catechins, a class of polyphenol, are abundant in tea. GT is the least oxidized and therefore has the highest concentration of catechins, followed by oolong which has a moderate amount of oxidation. BT is the most oxidized and contains the lowest catechin content [2]. Epigallocatechin-3-gallate (EGCG) is the most abundant catechin found in GT [3]. It is thought to be the most biologically active compound in GT and has been shown to have weight-reducing effects such as increasing energy expenditure and metabolism [4], decreasing body weight and body fat [5], decreasing energy absorption and increasing fat oxidation [6], enhancing insulin activity [7] and increasing sympathetic nervous system activity by inhibition of catechol-O-methyl transferase, the enzyme responsible for the breakdown of noradrenaline [8]. EGCG has other health promoting effects such as protection against atherosclerosis [9], [10], increasing bone mineral density [11] and reduction of ultraviolet light–induced inflammatory responses [12]. During processing of BT, most of the catechins are converted to theaflavins, theaflavin-3,3′-gallate, and thearubigins [13].
Although consumption of BT is more than 75% of total consumption, studies on the effects BT on body composition and glucose tolerance are limited. This study aimed to examine the effects of long-term consumption of GT and BT, at a biologically relevant dose, and a low dose of EGCG (1 mg/kg) that has been shown to have bioactive antioxidant effects [14], [15], on changes in body fat mass and changes in key transcription factors and enzymes involved in the maintenance of energy homeostasis in the liver, skeletal muscle, and adipose tissue. Based on previous work, it was hypothesized that development of long-term diet induced obesity and sequelae would be interrupted by all treatments due to EGCG content. Given the highest relative levels EGCG in GT, then BT, and finally, the low-dose EGCG, it was predicted that the greatest reductions of fat mass, glucose intolerance, and increases in gene expression related to energy expenditure, metabolism, and increasing fat oxidation would be observed in the GT group followed by the BT then EGCG groups.
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Animals and treatments
Male Sprague Dawley rats (n = 48) were purchased from the Animal Resource Centre (Canning Vale, Western Australia) at 3 weeks of age. Animals were allowed to acclimate for 1 week on chow and water. From 4 weeks of age, all animals were provided with a semisynthetic, high-fat diet (15% fat, Specialty Feeds, Glen Forrest, Western Australia) (see Table 1) and provided one of 4 drinking fluids: GT, BT, EGCG, or water (Control). Tea and EGCG solutions were given as 100% of their fluid intake. Rats
Ingestive behavior and body weight
Animals provided with GT had a fluid intake that was significantly lower than control animals (weeks 1–17, P's < .05) (Fig. 1A). The EGCG group also had a lower fluid intake compared with control animals (weeks 7–11, P's < .05) (Fig. 1A). BT animals had a higher fluid intake towards the end of the experimental period (weeks 22-25, P's < .05) (Fig. 1A). There were no other significant differences in fluid intake between the treatment groups and the control group.
There were no significant
Discussion
Tea and catechin drinking reduced body fat mass while sparing, or increasing, fat free mass and improving glucose tolerance. These physiological changes were accompanied by alterations in a number of genes within adipose tissue and liver, but not skeletal muscle. Furthermore, tea drinking primarily increased the expression of genes involved in fatty acid metabolism in the liver, whereas EGCG treatment primarily increased markers of adipocyte differentiation and metabolism in perirenal adipose
Acknowledgment
The authors wish to thank Margaret Morris for her assistance with the leptin radioimmunoassay. Nora Chen was the recipient of a Duetche Bank Postgraduate scholarship. This work was supported by the National Health and Medical Research Council of Australia (217011, 350313) and the Australian Research Council (DP0346830). The authors declare no conflict of interest.
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