Recent estimates indicate that about  1/3 of the adult population in the US is obese [Centers for Disease Control and Prevention, 2009] and while 2011 estimates in Canada indicate that approximately 1/5 of Canadians adults are classified as obese based on self-reported height and weight [Statistics Canada], studies have found that obesity rates in self-reported weight is ~7.4% higher when based on measured height and weight [Shields et al].  Adjusting for this under self-reporting of weight, > 1/4 (25.6%) of the adult population in Canada would be considered obese. 

Recent literature suggests that obesity and the related diseases of “metabolic syndrome” associated with obesity are not just a North American problem either, but a global health problem [Popkin]. Although there are many genetic and environmental factors that may predispose people to weight gain, the main cause of overweight and obesity is believed to be an imbalance between dietary intake and energy expenditure (i.e. calories in > calories out).  Excess fat mass develops over time from a very small positive energy imbalance i.e. just taking in slightly more calories than needed.  

In general, average weight gain per year is small; approximately 1 pound per year across all race, economic, and sex groups [Brown]. There are many strategies used to address weight gain, including;

• Dietary approaches; which usually focus on decreasing caloric intake through a variety of means and while some people go on self-chosen “diets” that are bizarre and even dangerous, weight loss will occur as long as energy intake is less than energy expenditure (i.e. calories in < calories out).
• Lifestyle strategies that help individuals identify and modify their eating behaviour and patterns of eating.  When people understand why they eat and when they eat, it is easier for them to make long-term lifestyle changes.
• Exercise and increased physical activity to help people attain and maintain a healthy body weight.
• Food intake is sometimes addressed pharmacologically by doctors by using drugs such as Orlistat (which blocks lipase, an enzyme involved in fat absorption).
• Surgical approaches provide the most dramatic weight loss and outside of the cosmetic value, may have a role in reducing long-term mortality and the incidence of diabetes [Bray].

ROLE OF GREEN TEA CATECHINS IN WEIGHT LOSS

Green tea is the unfermented leaves of the Camellia sinensis plant and contains a number of biologically active compounds called catechins and epigallocatechin gallate makes up almost 30% of the solids in green tea [Kim et al].  Recent studies have found that green tea catechins, especially EGCG play a significant role in both weight loss and body fat composition.

Green Tea Catechins and “Metabolic Syndrome”

Several large-scale population studies have linked increased green tea consumption with significant reductions in “metabolic syndrome” which is a cluster of diseases that include;

• insulin resistance or diabetes
• hyperinsulinemia (high levels of insulin in the blood)
• cardiovascular diseases; high blood pressure & coronary heart disease
• obesity

It is thought that epigallocatechin gallate (EGCG), the most abundant catechin in green tea, mimics the actions of insulin. This has positive health implications for people with insulin resistance or diabetes [Kao et al] and EGCG also lowers blood pressure almost as effectively as the ACE-inhibitor drug, Enalapril, having significant implications for people with cardiovascular disease [Kim et al].

Green Tea in Population Studies

Population studies and several randomized controlled studies (where one group is “treated” and the other group is not) have shown that waist circumference is smaller and levels of body fat is less the more green tea consumed  [Phung et al] .The anti-obesity effects of green tea are usually attributed to the presence of catechins [Naigle].

Green Tea Catechins

While catechins make up ~ 30% of green tea’s dry weight (of which 60–80% are catechins) oolong and black tea, which are produced from partially fermented or completely fermented tea leaves contains approximately half the catechin content of green tea.

Drinking 8-10 cups of green tea per day is enough to increase blood levels of EGCG into a measurably significant range [Kim et al]. Matcha, a powdered green tea used in the Japanese tea ceremony and popular in cold green tea beverages such as bubble tea, contains 137 times greater concentration of EGCG than China Green Tips (Mao Jian) tea [Weiss et al].

Green Tea Catechin Content of Brewed Green Tea vs Matcha Powder

A typical cup (250 ml) of brewed green tea contains 50–100 mg catechins and 30–40 mg caffeine, with the amount of tea leaves, water temperature and brewing time all affecting the green tea catechin content in each cup.

A gram (~1/3 tsp) of matcha powder contains 105 mg of catechins (of which 61 mg are EGCs) and contains 35 mg of caffeine. Most matcha drinks made at local tea and coffee houses are made and served cold and contain ~1 tsp of matcha powder which contains ~315 mg of catechins (of which ~183 mg are EGCs).  Since there is no brewing time involved in the preparation of cold matcha beverages, the amount of catechins remains relatively constant in each cup. Variation in catechin content in matcha powder is largely due to where the plant is grown and how it is processed.

Weight Loss Effect of Green Tea Catechins

Metastudies of 11 green tea catechin studies found that subjects consuming between 270 to 1200 mg green tea catechins / day (i.e. 1 – 4 tsp of matcha powder per day) lost an average of 1.31 kg (~ 3 lbs) over 12 weeks [Hursel].

Decreased Body Fat & Abdominal Fat even without Significant Weight Loss

The effect of green tea catechins on body composition is significant even when the weight loss between “treated” and “untreated” groups is small (~5 lbs in 12 weeks)

Even with such small amounts of weight loss;

•  the total amount of abdominal fat decreases 25 times more with green tea catechin consumption than without  (−7.7 vs. −0.3%)
• total amount of subcutaneous abdominal fat (the fat just below the skin of the abdomen) decreases almost 8 times more with green tea catechin consumption thank without it (−6.2 vs. 0.8%).

How do Green Tea Catechins Work?

The mechanisms by which green tea catechins reduce body weight and reduce the amount of total body fat and in particular reduce the amount of abdominal fat are still being investigated.  It is currently thought that green tea catechins;

• increased thermogenesis; i.e. increased heat production which would result in increased energy expenditure (or calorie burning)
• increase fat oxidation (or using body fat as energy)
• decrease appetite
• down-regulation of enzymes involved in liver fat metabolism
• decrease nutrient absorption

Green Tea Absorption

Green tea catechins are absorbed in the intestine.  Since the presence of food significantly decreases their absorption, green tea catechins are best taken 1/2 an hour before meals or 2 hours after meals.

The timing of green tea catechin intake may also affect the absorption and metabolism of glucose.  A study by Park et al found that when green tea catechins were given one hour before to a glucose (sugar) load, glucose uptake was inhibited and was also accompanied by an increase in insulin levels. Taking green tea catechins an hour before consuming highly sweet foods may be beneficial for those with insulin resistance or diabetes.

Green Tea Catechins and Milk

There seems to be some dispute in the literature as to whether the casein (a protein) in milk binds green tea catechins, making them unavailable for absorption in the body, which is why matcha drinks are often made with non-milk beverages such as soy milk, almond milk or rice milk (that don’t have casein).

Conclusion

Consuming between 1 – 4 tsp of matcha powder per day (270 to 1200 mg green tea catechins / day) is sufficient to result in weight loss of approximately 3 lbs in 12 weeks (with no other dietary or activity changes) and to significantly decrease body fat composition and reduce the quantity of abdominal fat.

Warning to pregnant women

While EGCG has also been found to be similar in its effect to etoposide anddoxorubicin, a potent anti-cancer drug used in chemotherapy [Bandele et al], high intake of polyphenolic compounds during pregnancy is suspected to increase risk of neonatal leukemia. Bioflavonoid supplements (including green tea catechins) should not be used by pregnant women [Paolini et al].

Recipe for Iced Matcha

For those of you that have been asking what Teamwork’s Registered Dietitian, Joy Kiddie is always drinking in that thermos…this is it!

Ingredients

• 1 tsp matcha (green tea) powder (contains ~315 mg catechins)
• 500 ml soy milk
• crushed ice

Method

1. Place 1 tsp matcha powder in a small stainless steel sieve and gently press through the sieve into a small bowl with the back of a small spoon
2. Put the sieved matcha powder into a ceramic or glass bowl (not metal, as the tannins in the tea will react and give the beverage and “off” metalic taste)
3. With a bamboo whisk (available at Japanese and Korean grocery stores), whisk 3 Tbsp boiled and cooled water into the matcha powder, until all the lumps are gone and the mixture is smooth
4. Place 1/4 cup of crushed ice in the bottom of a tall (16 oz / 500 ml) glass
5. Pour matcha and water mixture over ice in the glass

*  Joy uses 2/3 unsweetened soy milk and 1/3 sweetened soy milk

Note: once the matcha is blended with the soy milk, the tannins in the green tea are neutralized and no longer react with metal, so the beverage can then be put in an insulated stainless steel cup.
Article by Joy Y. Kiddie MSc, RD – Registered Dietitian with Teamworks Health Clinic

References

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Park JH, Jin JY, Baek WK, Park SH, Sung HY, Kim YK, et al. Ambivalent role of gallated catechins in glucose tolerance in humans: a novel insight into nonabsorbable gallated catechin-derived inhibitors of glucose absorption. J Phyisiol Pharmacol 2009;60:101–9.

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Paolini, M, Sapone, A, Valgimigli, L, “Avoidance of bioflavonoid supplements during pregnancy: a pathway to infant leukemia?”. Mutat Res 527 (1–2): 99–101. (Jun 2003)

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Statistics Canada (StatsCan), http://www.statcan.gc.ca/pub/82-003-x/2008002/article/10569-eng.htm

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