Green Tea, for a last couple of years has become a hot topic of discussion in the health and fitness universe. Right from the different types of teas, be it Green, White, Black, Oolong, etc. to the amazing health benefits these teas offer, the tea lovers, swear by the effectiveness of their daily poison. But the hottest topic pertaining to teas, primarily green teas, is green tea and weight loss.
In fact, weight loss is such a hot topic that you can see ears getting erect and eyes sparkling, the moment someone mentions it. The phenomena of green tea and weight loss is an old topic of debate, with many overhyping the seemingly little effect it has.
With an analysis of strong research, let’s unearth the unbiased truth on the topic of green tea and weight loss .
In a 2014 study in the Austin Journal of Clinical Medicine, a Saudi Arabian research team, led by Rokia Al-Salafi , analysed multiple studies to assess the mechanism of green tea and weight loss. They found the following mechanisms by which green tea exerts its effects:
On 3 separate occasions, 10 subjects were assigned among 3 treatments: green tea extract (50mg caffeine and 90mg epigallocatechin gallate), caffeine (50mg), and placebo, which they ingested at breakfast, lunch, and dinner.
Relative to placebo, treatment with the green tea extract resulted in a significant increase in 24-h EE. Twenty-four-hour urinary norepinephrine excretion was higher during treatment with the green tea extract than with the placebo. Thus, green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both.
During each stay, the subjects ingested a capsule of placebo or capsules containing 200mg caffeine and a variable dose of EGCG (90, 200, 300 or 400mg) three times daily, 30min before standardized meals.
Twenty-four hour energy expenditure increased significantly with all EGCG-caffeine mixtures compared with placebo. No effect of the EGCG-caffeine mixture was observed for lipid oxidation. Systolic and diastolic blood pressure increased by about 7 and 5 mmHg, respectively, with the EGCG-caffeine mixtures compared with placebo.
Healthy Japanese men were divided into 2 groups. A 12-wk double-blind study was performed in which the subjects ingested 1 bottle oolong tea/d containing 690mg catechins (green tea extract group) or 1 bottle oolong tea/d containing 22mg catechins (control group).
Body weight, BMI, waist circumference, body fat mass, and subcutaneous fat area were significantly lower in the green tea extract group than in the control group.
Researchers saw that, high caffeine consumers reduced weight, fat mass, and waist circumference more than low caffeine consumers; resting energy expenditure was reduced less and respiratory quotient was reduced more during weight loss.
In the low caffeine consumers, during WM, green tea still reduced body weight, waist, respiratory quotient and body fat, whereas resting energy expenditure was increased compared with placebo. In the high caffeine consumers, no effects of the green tea-caffeine mixture were observed during WM.
Thus, high caffeine intake was associated with weight loss through thermogenesis and fat oxidation and with suppressed leptin (appetite) in women. In habitual low caffeine consumers, the green tea-caffeine mixture improved WM, partly through thermogenesis and fat oxidation.
The results demonstrated enhancement in dietary fat oxidation and DIT as the result of the long-term ingestion of tea catechin. Dietary induced thermogenesis (DIT), defined as an increased energy expenditure from the fasting baseline for 8 hr after the single ingestion of a test meal.
Forty-six overweight women were fed in energy balance from day 1 to day 3, followed by a LED with GT (1125mg tea catechins +225mg caffeine/d) or placebo (PLAC) from day 4 to day 87. Caffeine intake was standardised to 300mg/d.
Researchers found that, reductions in weight, BMI, waist:hip ratio, fat mass and fat-free mass were not statistically different between treatments. REE as a function of fat-free mass and fat mass was significantly reduced over 32d in the PLAC group but not in the GT group. The GT group became more hungry over time and less thirsty, and showed increased prospective food consumption compared with PLAC. Taken together, the ingestion of GT along with a LED had no additional benefit for any measures of body weight or body composition.
Researchers found that, the body weight of the green tea group decreased by a non-significant 2.4% after treatment; whereas the body weight, body mass index (BMI), and body fat content of the control group were significantly higher after 3 months. There were no differences in any of the hormone levels measured in either group. Thus, green tea supplementation did not significantly reduce body weight in obese women with PCOS, nor did it alter the glucose or lipid metabolism.
There was only a 0.3% reduction in BW (0.15 kg) after 12 weeks of treatment with GTE. There was no statistical difference in % reduction in BW, BMI and waist circumference between the GTE and placebo groups.
Two studies were performed. In study A, 12 healthy men performed a 30-min cycling exercise at 60% of maximal oxygen consumption (VO2max) before and after supplementation. In study B, 11 healthy men took an oral-glucose-tolerance test before and after supplementation. In the 24h period before the experimental trials, participants ingested 3 capsules containing either GTE or a placebo.
Researchers found that, the average fat oxidation rates were 17% higher after ingestion of GTE than after ingestion of placebo. Moreover, the contribution of fat oxidation to total energy expenditure was also significantly higher, by a similar percentage, after GTE supplementation. The insulin decreased in both the GTE and placebo trials, and there was a increase of 13% in insulin sensitivity.
A very-low-energy diet intervention during 4 wk was followed by 3 months of WM; during the WM period, the subjects received a green tea-caffeine mixture (270mg epigallocatechin gallate + 150mg caffeine/d) or placebo, both in addition to an adequate protein (AP) diet (50-60g protein/d) or an HP diet (100-120g protein/d). Subjects lost 7.0 +/- 1.6kg of body weight.
Researchers found that, the green tea-caffeine mixture, as well as the HP diet, improved WM independently through thermogenesis, fat oxidation, sparing FFM, and, for the HP diet, satiety; a possible synergistic effect failed to appear.
An assessment of 11 studies found that, an EGCG– caffeine mixture has an effect on WL and on WM after a period of negative energy balance. So, the effect was seen primarily with caffeine, and that too with diet/calorie control. The overall effect too was quite small, app. 1.3kg. On the other hand, the small effect also varied with ethnicity, where Caucasians were found to have a smaller effect than Asians. But the overall effect was not significant.
At week 12, the decrease in waist circumference was significantly greater in the catechin group than in the control group. Although the increase in Insulin at week 12 was significantly greater in the catechin group than in the control group, no apparent difference was noted between the two groups in glucose and hemoglobin A(1c).
Researchers found that catechin/caffeine combinations at these dosages had non-significant acute effects on EE and fat oxidation. The maximum observed effect on EE of about 2% could still be meaningful for energy balance over much longer period of exposure. However, higher short-term effects reported in the literature may reflect variations in green tea extracts, added caffeine, or synergies with physical activity.
The study found little benefit in consuming green-tea extract on fat oxidation or cycling performance, unlike caffeine, which did benefit cycling performance. Therefore, it was concluded that green-tea extract offers no additional benefit to cyclists over and above those achieved by using caffeine.
The results suggest that GT and BT suppressed adipocyte differentiation and fatty acid uptake into adipose tissue, while increasing fat synthesis and oxidation by the liver, without inducing hepatic fat accumulation. In contrast, EGCG increased markers of thermogenesis and differentiation in adipose tissue, while having no effect on liver or muscle tissues at this dose. These results show mechanisms by which tea and EGCG may improve glucose tolerance and support a role for these compounds in obesity prevention.
Researchers found a trend toward greater loss of body weight in the catechin group compared with the control group. Percentage changes in fat mass did not differ between the catechin and control groups. However, percentage changes in total abdominal fat area, subcutaneous abdominal fat area, and fasting serum triglycerides (TG) were greater in the catechin group. These findings suggest that green tea catechin consumption enhances exercise-induced changes in abdominal fat and serum TG.
Low EGCG increases postprandial fat oxidation in obese men and this to the same extent as 200mg caffeine, whereas high EGCG does not exert this effect. Fasting fat oxidation is increased only by caffeine (with or without EGCG). There is no synergism of low EGCG and 200mg caffeine. Energy expenditure is not affected by EGCG.
Researchers observed a decrease in estimated intra-abdominal fat area in the GT3 group. In addition, they found decreases of 1.9cm in waist circumference and 1.2kg body weight in the GT3 group vs. C. They also observed reductions in total body fat (GT2, 0.7kg) and body fat % (GT1, 0.6%). Researchers concluded that consumption of two servings of an extra high-catechin GT leads to improvements in body composition and reduces abdominal fatness in moderately overweight Chinese subjects.
On meta-analysis, GTCs with caffeine decreased BMI, body weight (-1.38 kg), and Waist circumference (-1.93cm) but not WHR compared with caffeine alone. GTC ingestion with caffeine also significantly decreased body weight (-0.44kg) when compared with a caffeine-free control. Studies that evaluated GTCs without caffeine administration did not show benefits.
Other potential mechanisms include modifications in appetite, up-regulation of enzymes involved in hepatic fat oxidation, and decreased nutrient absorption. However, most of the effect was seen in relation to the caffeine present and there are too many variations which need further study when it comes to the influences of dose, method of intake (e.g., empty or full stomach, supplement, brewed beverage, etc.), duration of intake, sex, degree of adiposity and potential positive interaction with physical activity.
Researchers found that, the catechin-caffeine mixtures and caffeine-only supplementation increased energy expenditure significantly over 24h.However, 24h fat oxidation was only increased by catechin-caffeine mixtures. Thus, compared with placebo, daily fat-oxidation was only significantly increased after catechin-caffeine mixtures ingestion.
Despite a similar increase in estimated energy intake during intervention period, body weight decreased by 0.64kg and increased by 0.53kg in the DGT and placebo groups, respectively, suggesting a protective effect of green tea catechins on weight gain.
Average visceral fat area, body weight, and body fat were reduced significantly by catechin-enriched green tea treatment but these effects were not seen in the control group. The decrease at week 12 in the visceral fat area in the catechin group was greater than that in the control group
In conclusion, the present results suggest that dietary supplementation with 300mg/d of EGCG for 12 weeks did not enhance energy-restricted diet-induced adiposity reductions, and did not improve weight-loss-induced changes in cardiometabolic risk factors in obese Caucasian women. The intake of 300mg/d of EGCG for 12 weeks did not cause any adverse effect on liver function biomarkers.
The effect seen in the analysis is similar to that seen in other studies, i.e. green tea or green tea extracts intake exerts no statistically significant effect on the weight of overweight or obese adults. There is a small effect on the decrease in the percentage of fat mass, but it is not clinically relevant.
No significant differences between groups and no significant changes over time were observed for the measured variables, like body composition, body fat, resting energy expenditure etc.
12 weeks of treatment with high-dose green tea extract resulted in significant weight loss, reduced waist circumference, and a consistent decrease in total cholesterol and LDL plasma levels without any side effects or adverse effects in women with central obesity. The anti-obesity mechanism of high-dose green tea extract might be associated in part with ghrelin secretion inhibition, leading to increased adiponectin levels. However, the word ‘significant’ actually referred to app. 1-1.2kg of weight loss after 12 weeks.
Combined results indicated that body weight (app.1.78 kg) and body mass index (BMI) did change significantly following green tea administration. The reduction in waist circumference (WC) after green tea consumption was significant in subjects in trials employing Green tea ≥800mg/day and with a treatment duration <12 weeks.
Now, the major difference again after 12 weeks of intervention was seen to be just 1.78kg, and that too when combined with a balanced and healthy diet and regular physical exercise.
In a 2012 study in The Cochrane Database of Systematic Reviews, a Canadian research team, led by Tannis M. Jurgens assessed the efficacy and safety of green tea preparations for weight loss and weight maintenance in overweight or obese adults. They found that:
With the later studies and other previous studies, the conclusion is similar:
Therefore, green tea or any other type of tea is no doubts an excellent beverage and has number of health benefits. But the effect on weight loss is very minimal. It’s no magic portion, as falsely claimed by many dieticians, coaches and websites. Stop convincing yourself that weight/fat loss will be greatly accelerated if you simply have the magical green tea. It won’t. The basics still remain the same, i.e. good old hard workouts and a clean diet.
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