Weight Loss Benefits of Green Tea
Since 1977, obesity has become an epidemic in the United States, and this has gradually affected the entire world. Starting about 10 years later, type 2 diabetes has also risen dramatically. Prevention and treatment strategies are global priorities.
A randomized controlled trial done in 2016 showed that green tea helped in the treatment of obesity. Numerous supplements have been purported to help with weight loss, but most fail when tested in a scientifically rigorous manner. Many miracle diet pills have come and gone. There were the prescription drugs like Fen-Phen, which, like the old street drug ‘speed’ caused weight loss, but also caused all kinds of heart problems. Fen-Phen could make you thin, but could also kill you. There was Orlistat, which blocks fat absorption. It caused weight loss, but also some bothersome side effects like diarrhea from all that mal-absorbed fat. Best advice for Orlistat? Don’t wear white pants. Then there was Meridia, which caused weight loss, but a little side effect like heart attacks and strokes caused it to be discontinued.
There was also weight loss supplements that wouldn’t kill you, but didn’t really work either. Green coffee, raspberry ketones and grapefruit extract all come to mind. They sound great, but they all turned out to be pure hype. One substance, though seems to have stood the test of time — green tea, with traditional Asian medicine touting the weight loss effects for thousands of years.
Modern randomized trials are just now demonstrating the benefits of tea for cardiovascular disease, high blood pressure and cholesterol. Green tea is particularly beneficial due to it’s high concentration of EGCG, a type of catechin (50–80% of total catechins in green tea). Catechins are absorbed in the intestine, but the presence of food significantly decreases absorption. Studies often use green tea extracts due to the dose needed, but also because the bio-availability in extracts is much higher than brewed tea. Typically a cup of brewed tea may have 70–100 g of catechins. Using a cold brew crystal process such as Pique Tea have about triple that amount per cup.
In the 2016 randomized, placebo controlled trial, researchers used a fairly high dose of EGCG of 856 mg, which required high dose green tea extract (GTE). Trying to drink this much from hot brewed green tea is daunting as it would require 12 cups per day. Supplements have high placebo effects, so randomization and placebo controlling is important. If people believe a supplement will make them lose weight, it generally will, no matter what it is. In order to maximize extraction of EGCG, the GTE was prepared by steeping green tea leaves in pure water at 90 C three times for 20 minutes each, then cooling the extract to preserve the catechin content. The extract was dried under low temperature and pressure conditions and also decaffeinated.
The GTE lowered body weight by about 1 kg and reduced the waist circumference as well. The placebo, by contrast did not reduce either body weight or waist size.
Ghrelin showed a trend towards lowering, but a significant difference when compared to the placebo group (not shown in this table). GTE reduced ghrelin from 621 to 529, where the placebo increased it from 599 to 664, so there was a big statistically significant difference between two groups.
Ghrelin is often referred to as the ‘hunger hormone’. If ghrelin is high, then you are hungrier. Anecdotal studies and personal experience have hinted at the appetite suppressing effect of green tea but this provides some rational basis for explaining how high dose catechin suppresses hunger. Adiponectin was also increased significantly, which is good although the exact significance is unknown. It has known anti-atherogenic and anti-diabetic properties, but this effect is not consistently seen in the literature.
Obviously, better hunger control hunger leads to eating less and weight loss. Hunger is a powerful obstacle because it is one of the most basic of human instincts. The three most powerful human needs are known as the 3F’s — Fluids, Feeding and Procreation. You may be able to temporarily ignore hunger, but when it persists for day after day, it becomes progressively more difficult to ignore. Controlling hunger is one of the keys to long term weight loss. Most calorie restriction plans ignore this factor, pretending it is all about will power. You can’t ‘decide’ to be less hungry. Fasting, on the other hand, tends to reduce overall hunger. Green tea, with its small effect on decreasing ghrelin is a great complement to fasting.
A 2009 meta-analysis had reached the same conclusion that green tea may cause a loss of 1.31 kg of body weight. Asians show consistently better results compared to Caucasians perhaps as a result of genetic differences in COMT (the enzyme blocked by catechins, discussed in previous post) activity, which can vary by as much as 3-fold. Asians have a higher frequency of the high-activity COMT variation, so therefore may benefit more from the inhibition of COMT by green tea catechins. Weight loss for Asians averaged 1.51 kg, but only 0.8 kg for Caucasians. However, 0.8kg is still a substantial benefit.
The other major differences between Asian and Caucasian populations include the typical Asian preference for green or oolong tea versus black (higher levels of catechins) and the fact that Asians often drink tea like water, so drink more throughout the day.
Caffeine itself may play a synergistic role in increasing metabolic rate. A meta-analysis of 15 studies showed that shows that green tea catechins given with caffeine was able to decrease body weight compared to catechins given alone. I will note that green tea does in fact contain some caffeine, whereas green tea extracts are may or may not contain it. Some studies sugges that regular and high caffeine usage may blunt the benefits of the GTE. In one study, using more than 300 mg/day of caffeine daily negated much of the benefits (a cup of brewed green tea only has 30 mg caffeine). Caucasian population typically drink more coffee and perhaps higher doses of catechins are necessary for benefits.
In addition to effects to suppress hunger, the increased noradrenalin may act to increase 24 hour energyexpenditure. A small randomized controlled trial of green tea extract increased caloric expenditure by 4%. A meta-analysis of studies on the increased energy expenditurealso generally found a synergistic effect of catechins and caffeine.
Ancient traditional Chinese medicine believes tea to have weight loss effects, and these beliefs are increasing found since the 1990s in westernized world as natural herbs that may increase energy expenditure. The stimulatory effects of the catechin-caffeine combination is greater than caffeine alone. Fat oxidation (the burning of fat for energy) increases with the catechin+caffeine but not so much with the caffeine alone group, except perhaps at very high doses.
Oolong tea may also show this beneficial effect and raises energy expenditure by 2.9%. Oolong tea is fermented and the catechins are partially converted to theaflavins. Oolong tea is not fully fermented like black tea, and thus represents a sort of mid-way between green and black tea. It is very popular in China and Japan.
Based on studies such as these, the optimal supplement would provide high doses of catechins with a smaller dose of caffeine (ie. not decaffeinated). This would have all the benefits of hunger suppression, increased energy expenditure, and fat oxidation. The dose would require 10 cups of green tea per day, but by using a cold brew technique, we can get this down to 3 cups per day in a easy to use formulation.