Green tea

The positive effects of green tea on health have been demonstrated by several scientific studies. For example, green tea may help prevent cardiovascular disease, and the polyphenols may reduce cholesterol deposits on the blood vessels. This tea also helps make the brain sharper and more alert.

But there are even more benefits. Green tea may also have a positive effect when you want to lose weight. Below you can read exactly why that is and how much tea you would need to drink for it.

Green tea as fat burners
What is green tea?
Polyphenols, catechins, ECGC
Green tea as a fat burner
Green tea as a fat burner: long-term effect
Reliable research?
Satiety and saturation
Conclusion

Green tea as fat burners

Green tea (extract), together with caffeine, is one of the few truly effective and legal fat burners. Although the research is not entirely consistent, most studies seem to support this conclusion. The extent to which it actually contributes to less body fat, however, appears to be limited.

What is green tea?

First, a quick distinction between the different types of tea: black, green and oolong. These actually come from the same type of tea leaves. The different tea plants, country of origin and other influences determine the taste. The way the leaves are processed, however, determines the type.

During the processing of black tea and oolong, the leaves are dried in the open air, where they react with oxygen. This process is called oxidation. It causes the leaves to lose their green color and take on a dark, golden-brown color. With green tea, the leaves are briefly steamed instead. This kills the enzymes needed for oxidation. As a result, they retain their green color. The tea made from them also retains a green color.

Because of this oxidation, the tea loses a large part of its polyphenols. Green tea, for example, contains almost 40 percent polyphenols, while black tea contains less than 10 percent. These polyphenols are precisely what provide the positive health properties. Incidentally, these polyphenols are not only found in tea, but also in herbs, fruit, vegetables and nuts. Polyphenols are actually chemical compounds and act as antioxidants.

The polyphenols in green tea contain the so-called catechins, which in studies on laboratory animals had very positive effects on the prevention of certain forms of cancer because they neutralize free radicals. Extensive research is still being done into the positive effects of catechins in humans.

Polyphenols, catechins, ECGC

The beneficial effect of tea is often attributed to catechins, a collective name for polyphenols (chemical compounds found in plants that act as antioxidants)(1). EGCG in particular, or in full epigallocatechin-3-gallate, is said to be responsible for many of these effects, whether or not its effect is strengthened by the other catechins. During the fermentation process of black and oolong tea, most catechins are converted into other substances called theaflavins, thearubigins and theabrownins (2).

Because leaves for green tea are not fermented, they have the highest EGCG content. As much as 50% of the catechins in green tea are EGCG.

Green tea as a fat burner

The acute effects (in the 24 hours after intake) of green tea extract are unclear (3,4). Many of the studies on this also combined green tea extract with caffeine, making it difficult to demonstrate the individual added value of both substances. Part I of this series is not about caffeine as a fat burner for nothing. In addition, it is not clear whether effects seen in combination also occur (and to the same extent) when one of the two is taken separately. Green tea itself also contains caffeine, about 2-4 percent. However, when we look at the amounts of caffeine in many of these studies, the amount of caffeine is greater than the amount naturally found in green tea.

What was interesting, therefore, were the differences between the people who took a supplement with only green tea and the people who combined it with caffeine. The people who received green tea extract in addition to caffeine lost weight faster than the people who had received only caffeine (5). Green tea therefore at least had added value to the effect of caffeine. However, that still does not make clear what it does apart from caffeine.

It is also not clear what in the tea causes this effect. Most studies therefore look at epigallocatechin gallate (EGCG), but also at other catechins. However, when these catechins were administered in different ratios and amounts, this did not lead to different results (6). If mainly these catechins caused the fat-burning effect, different amounts and ratios should have shown different results. So it is not clear what the acute effects of green tea extract are, in what amounts and in what ratio the various catechins in it work best, if they are responsible for an effect at all.

Green tea as a fat burner: long-term effect

Japanese study: "Faster fat burning through intake of green tea extract"

As for the long-term effects, things look slightly more positive (1). Still, here too it is the tea catechins that were used. In 2005, Japanese researchers gave their subjects a drink with a low dose of catechins (78 mg/day) or a high dose (593mg/day) every day for 12 weeks (7). You can see the overview of the different catechins in this drink in the image on the right. In addition, after 4, 8 and 12 weeks, they gave the subjects a meal containing "labeled" fats. This means fats in which a specific carbon atom has been made recognizable (using so-called "13C isotope labeling"). This allowed the researchers, by measuring breathing, to determine how much of these fats were burned. After week 12, the group that had received the high dose of tea catechins turned out to burn more of the labeled fats.

In addition or as a result, total energy expenditure in the 8 hours after eating a meal (dietary induced thermogenesis, D.I.T) also appeared to increase from 51.4 to 90.3 kcal. So it cost more energy to process the meal. D.I.T is responsible for only 10% of our total energy expenditure, 60-75% comes from resting metabolism and about 20% of energy is used by daily activity (7). Still, the daily 10% of energy that eating a meal costs appears to play a major role in obesity (8).

Reliable research?

Caffeine was also used in this last study. Because they did not use green tea, but only the catechins, you might think the caffeine was added to mimic the ratio in green tea. However, green tea contains 10 to 15 times as many catechins as caffeine. In the table at the top right, you can see that the study used proportionally much more caffeine. In the case of the low catechin dose, there was even as much caffeine as catechins. Nowhere in the entire study is it explained why this amount of caffeine was added. So once again the question is what effect the catechins would have if no or less caffeine had been added.

Moreover, you often hear me say: "Researchers from this or that university". In this case, the researchers worked for Health Care Products Research No. 1, Kao Corporation. That immediately makes me wonder whether this company itself benefits from the sale of green tea. In any case, the study itself does not state that there are no conflicts of interest, as is normally customary in independent studies. So I Googled a bit further for "Kao corporation green tea" and, sure enough, they sell green tea themselves (image left). Then it suddenly becomes a lot more understandable that so much caffeine was used. Since they say nothing about the caffeine, they can attribute all effects to the catechins from green tea in order to promote their product.

I already found it strange that no control group was used in this study. After all, you can now only see that the high dose had a greater effect than the low dose, but you do not know what effect the low dose has compared with a placebo.

Study on the effect of green tea extract on body composition in Thai people with obesity

Thai researchers from Khon Kaen University (that is what I mean) did this better (9). First of all, they used a control group that received a placebo and compared it with green tea, instead of comparing two dosages with each other. Moreover, the chance is therefore greater that this study was objective. The researchers gave 60 overweight Thai men and women a capsule with 250 grams of green tea extract three times a day (after meals). In total, these capsules contained about 48mg of catechins and 4mg of caffeine. This is already more similar to the catechin-caffeine ratios as they occur in green tea.

After 12 weeks, they looked at the effects on body composition. Among other things, weight, BMI, body fat percentage and waist and hip circumference (image below) were measured. Weight in the test group decreased significantly, while there was no decrease in the placebo group. Also when we look at the other figures, such as body fat percentage and circumference, we see that the test group achieved considerably better results.

In this study, the decreased respiratory quotient (RQ), the ratio between inhaled oxygen and exhaled carbon dioxide, also showed that the burning of food (the previously mentioned D.I.T) cost more energy after intake of green tea. In the placebo group, the decrease in RQ after 8 weeks was significantly smaller.

Satiety and saturation

No, it is not a typo. I want to discuss two types of satiety or saturation. First, satiety in terms of hunger. More satiety means less hunger and therefore less urge to eat. Satiety increased considerably in the test group, but even more in the control group. Statistically, there was no significant difference. This is in contrast to earlier animal studies in which green tea led to higher satiety (10,11). Those studies used higher dosages, which may explain the difference. The Thai researchers also take into account that if the same amount of green tea extract were drunk in pure tea form, with hot water, this would lead to greater satiety.

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By the other form of saturation I mean the temporary effect of green tea. In both the graph and the table, you can see that the effects of the green tea last until about the eighth week. Up to and including week 8, we only see improvement in the test group, but in week 12 all figures look worse. The people became heavier again, had more fat and a larger circumference. That they already had a diet that leads to being overweight was clear. After all, this had led to an average body fat percentage of almost 40% and a BMI of 27. That is what they were selected for. Until week 8, the green tea extract could stop this increase in weight and even lead to less weight and body fat. After those eight weeks, however, not only does weight loss stop, people actually start gaining weight again. It therefore seems as if your body becomes saturated with green tea or the catechins in it. How long you would need to stop using green tea (extract) to achieve this effect again is not known.

Here I also have to refer back to the studies in part I of this article, which showed that a supplement with green tea and caffeine appeared to have less effect on people who regularly drink coffee. This is an additional reason to wonder whether, in this Thai study, caffeine was responsible for all effects and whether daily intake led to saturation with caffeine rather than saturation with catechins.

Various studies on green tea and body fat: studies funded by manufacturers are positive, but not reliable

I have discussed the last-mentioned study in somewhat more detail because of the insight it offered into the temporary effect of green tea extract and saturation. In addition, there are other studies in which body fat percentage was examined under the influence of green tea (12 through 15). Two of these with positive outcomes were also carried out by researchers from the Kao Corporation, which sells green tea products itself (12,14).

A third study is not from the Kao Corporation, but from Unilever R&D (Research & Development). Besides the fact that its objectivity can be questioned, large doses of caffeine were added. As mentioned, green tea normally contains 10 to 15 times as many catechins as caffeine. For this study, however, the ratio was not 10-15:1, but 4:1. The researchers gave three different dosages of catechins to compare them. At the higher catechin dosages, however, the caffeine dosage was also higher. The researchers say that the high catechin dose produced the best result in terms of body fat loss and waist circumference, but that could also be due to the higher intake of caffeine. The reason it contains so much caffeine, according to the researchers, is that this is the ratio found in many Chinese commercial green tea products. That is fine if you want to assess the added value of these commercial drinks. However, the study was about the effect of green tea, in this case enriched with catechins. The addition of the high dose of caffeine again seems to have been done to ensure successful results.

Independent green tea studies show a mixed picture

This feeling becomes even stronger because of the following study. Researchers from the University of South Australia had 38 overweight women walk for 45 minutes three times a week (at an intensity of 75% of maximum heart rate)(13). Part of the group also took 150mg of the catechin epigallocatechin gallate (EGCG) twice a day (as mentioned earlier, the catechin to which most fat-burning effects are attributed). In this case, it was in the form of "Teavigo", a DSM product that contains EGCG. The rest received a placebo. DSM promotes Teavigo as " the purest form of caffeine-free green tea extract on the market today" (16). So it contains no caffeine.

Waist circumference (p < 0.01), total body fat (p < 0.02), abdominal fat (by DXA) (p < 0.01) and intra abdominal adipose tissue (by CT) (p < 0.01) were reduced in both treatment groups, with no difference between placebo and Teavigo. Teavigo significantly decreased resting HR (p < 0.01) and reduced plasma glucose in subjects with impaired glucose tolerance (p < 0.05).
A.M. Hill, University of South Australia

Belly fat ("visceral fat"/"organ fat") and subcutaneous fat (fat under the skin) decreased by the same amount in both groups. The green tea therefore had no effect compared with the placebo. So there was no caffeine and there was no effect. Again, this is a reason to wonder whether only the caffeine in other studies is responsible for the fat-burning effect.

"Green tea has no effect on resting metabolism"

Researchers from Maastricht University were also not positive about the effects of green tea (17). They specifically looked at the effect on resting metabolism (the previously mentioned energy expenditure at rest, which accounts for 60-75% of total energy expenditure). In addition, they looked at the effect on body weight, BMI, body fat and fat-free mass. On all these points, there was no difference in the results of the group that received green tea and the group that received a placebo. Both groups lost weight to a similar extent. The weight loss itself was to be expected, given that the group consisted of overweight women who were placed on a low-calorie diet during the study.

As for resting metabolism, you would expect it to decrease because body mass decreases (lean mass did not increase, or increased less than the decrease in body fat). When there is less body mass, the body needs less energy to maintain it (hence the advantage of having a lot of muscle mass when trying to get or stay lean). In the group that had received green tea, resting metabolism did not decrease significantly; in the placebo group it did. However, the limitation of the decrease in resting metabolism was therefore not enough to lead to a better result.

Although the decrease in REE as a function of fat-free mass and fat mass was not significant with GT treatment, whereas it was with PLAC treatment, no significant effect of treatment over time was seen, suggesting that a robust limitation of REE reduction during a LED was not achieved by GT.*

* REE=Resting energy expenditure/resting metabolism, GT=Green Tea, PLAC=Placebo, LED=Low energy diet
K. Diepvens, Maastricht University

Incidentally, it is striking that the "green tea" here also consisted of 4/5 catechins (1125mg/day) and 1/5 caffeine (225mg/day). Unlike in the other studies, this large amount of caffeine did not provide an advantage. So I immediately wonder whether these heavy women happened to drink a lot of coffee and therefore no longer gained any benefit. Guess what, this indeed appears to be very possible. The women in the Maastricht researchers' study were "moderate coffee drinkers"; they consumed on average between 200mg and 400mg of caffeine per day. In the earlier-mentioned study showing that people who drank a lot of coffee no longer benefited from caffeine intake, the dividing line between a lot and little coffee was 300mg per day. It may therefore be that some women were below 300 and did see improvement, while others were above it and saw no difference. Since the relationship between daily caffeine intake and effect on body composition was not examined specifically, it is not clear whether this is the cause.

Effect of green tea on metabolism during activity

As mentioned, your body uses energy in three different ways: at rest, during activity and while digesting food. The effect on resting metabolism appeared limited, as we saw in the Maastricht study (17). The energy cost of digesting food increases with intake of green tea, as shown by the Japanese study, but the objectivity of that study can be questioned (7).

That leaves metabolism during activity, meaning how much energy you use when, for example, you are cycling or running. Several studies have shown that this increases when green tea is taken before the activity (18 through 22).

Researchers from The University of Birmingham had 12 men do 30 minutes of cardio on a bike (intensity 60% VO2max)(21). This happened under two conditions:

After taking a capsule with green tea extract (476mg catechins, of which 136mg EGCG).
Without taking the capsule. There were two weeks between these conditions.

With intake of the capsule, 17% more fatty acids were burned while less use was made of carbohydrates (image right). The ratio of fats or sugars used therefore shifted more toward fats, and of course we like to see that!

Comparable results are seen in a study from Japan, once again unfortunately from the Kao Corporation. Fourteen healthy young men between 26 and 42 years old received a drink with (570mg) tea catechins or a placebo for two months. During those two months, the men walked 5km on a treadmill three times a week. With the catechins, almost 30% more was burned from fats and 18% less from carbohydrates.

This effect was not seen in a study in which only 70mg of catechins was given for three weeks (23).

Conclusion

Because the tea leaves for green tea are not dried in the air, they retain their green color and a high catechin content, specifically EGCG.
The acute effects on metabolism after intake of green tea or the catechins in it are unclear. Good results have been achieved, but in combination with caffeine.
The same applies to many studies on the long-term effects, such as resting metabolism. Besides the fact that these are often combined with caffeine, many of the studies are not objective, but commissioned by manufacturers of green tea. An objective study that found an increased resting metabolism (again in combination with caffeine) did not see this result in more weight loss than in a placebo group.
Depending on the dose, intake of green tea extract may possibly increase energy expenditure during activity; this extra burning comes mainly from fats.

A lot of caveats, then, and not exactly a very convincing piece. We see that tea can contribute to increased fat burning, especially during activity. Despite all the caveats, tea and caffeine still have the best demonstrated fat-burning effect. However, that says as much about the limited added value of tea and caffeine as it does about the even less proven effect of other so-called fat burners.

So I stand by the statement that these are the only legal fat burners for which research has shown that they really work. The extent to which they do this and ultimately lead to results, however, appears so limited that, as usual, you can expect much more from a good eating pattern and sufficient exercise.

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