In men and women, the degree of body fat, whether expressed as percent body fat or the ratio of waist circumference to hip circumference, tends to decrease as green tea intake increases. Green tea contributes to the maintenance of healthy body weight in several ways.
One of the least appreciated qualities of green tea is its ability to limit the absorption of fat intake from the diet. This process occurs because Green tea catechins - especially EGCG - interfere with the lipase - fat-digesting - enzymes in the small intestine and stomach. Since the fats are not completely digested, lipid droplets are produced that cannot enter intestinal cells, and so they remain unabsorbed. This chain of action has produced a significant decrease in the absorption of dietary fats by rats consuming green tea. Any interface with the efficient absorption and digestion of dietary fats could figure prominently in any effort to manage weight effectively, even though it is not proven how effective green tea is in blocking fat absorption in humans.
Green tea catechins not only decrease the efficiency of absorption of fatty acids from the diet, they also interfere with the production of fat for storage in adipose tissue depots. Green tea leaf extract that is both purified and rich in EGCG decreases the activity of fatty acid synthase, which is an enzyme that regulates how quickly the body produces fat for storage. This process is consistent with a body of literature recently analyzed in the journal Molecular Nutrition and Food Research, which shows how EGCG inhibits new fat formation - "lipogenesis" - and fat storage within adipocytes. Tea aids in the absorption of less fat from the diet, and can also interfere directly with the storage of fat in adipocytes, a dual mechanism for supporting healthy body weight.
The dominant green tea catechin, EGCG, also entices the body to shift some of its manner of producing energy from glucoseburning to fat-burning. There are two ways to accomplish this and EGCG seems to do both. First, if the amount of glucose available to tissues, especially the skeletal muscles, is reduced, then more fat must be metabolized to carbon dioxide and water in order to satisfy energy needs. During times when glucose is in short supply, the liver synthesizes glucose from a variety of precursors, including amino acids released by muscle cells. The first enzyme in this synthetic ("gluconeogenic") pathway, phosphoenolpyruvate carboxykinase (PEPCK), is inhibited by EGCG. Blocking this enzyme reduces the rate of formation of new glucose, requiring cells to switch to burning fat for energy.
In an example of exquisite biochemical coordination, EGCG also stimulates the conversion of fatty acids to energy. In cell culture studies, EGCG has increased the rate of utilization of fatty acid breakdown products instead of glucose to produce energy. In a series of experiments, mice, often studied because the way they obtain energy is pretty much the same as the way humans do, have responded to the addition of catechin-rich green tea extract to a high-fat diet with less weight gain and less fat accumulation within their bodies than mice fed the same high-fat diet but not fed catechins, despite eating just as much. This phenomenon has been studied in depth. In a recent study dietary supplementation of exercising mice with tea catechins forced skeletal muscles to switch from using their glycogen reserves as energy sources to increasing their reliance on burning fats from adipose depots. This "switch" is so reproducible that the researchers can predict when it will happen. The powerful phytonutrients (catechins) in green tea and green tea extract can recruit muscles to help stored fat get used up faster!
Thermogenesis, in humans. In one example of the fat-burning, thermogenic effects of green tea catechins, 24 hour heat production was calculated in slender healthy to overweight young men during times at which they were in a state of rest and consumed identical diets; they did not consume caffeine-containing foods or beverages, but they did intake either a placebo, 150 mg of caffeine alone or 150 mg of caffeine plus 270 mg of EGCG and 105 mg of other mixed catechins. Researchers observed that the intake of placebo or 150 mg of supplemental caffeine during a 12 hour period did not affect the utilization of glucose or fat in order to supply energy. However, the consumption of green tea catechins during a 12 hour period increased total energy expenditure and heat production in the same-day 24 hour period. It was found that increased fat-burning and decreased use of glucose for fuel caused this energy usage.
Because under the conditions of this experiment all energy expenditure was essentially "resting" energy expenditure, the catechin-induced increase in resting energy expenditure reflects enhanced thermogenesis. That is, more heat production as a "byproduct" of energy production. Since increased heat production to satisfy the same energy demand means that the efficiency of energy production decreased, more stored energy needed to be "burned" - accelerating the rate at which energy stored in fat depots would become depleted. Of course, as stored fat becomes depleted, both body weight and fat depot size decrease. The increase in fat utilization in this experiment, which was minimized by keeping the subjects in a "resting" state, could result in the loss of one pound of excess body weight in 1 to 2 months and a loss of 6 to 12 pounds in a year. Consistent with this rough prediction, overweight adults consuming 270 mg of EGCG daily for 3 months experienced an average loss of 4.6% of total body weight, with an average decrease in waist circumference of 4.5%. This thermogenic effect of green tea catechins, when combined with a healthy diet and exercise, could be extremely beneficial for those looking to support weight management efforts.
Beneficial results also were obtained in a "gold standard," randomized placebo-controlled clinical trial, published recently in the American Journal of Clinical Nutrition. In this study healthy men supplemented their diets with either 22 mg or 690 mg of total catechins daily for 12 weeks. At the end of the experiment, the men who were consuming 690 mg of total catechins daily had lost more weight, more inches off their waist, more total body fat and more abdominal fat.
What about Stress and Abdominal Fat?
A growing body of evidence indicates that in both men and women, stress and mood issues are associated with increased abdominal fat storage and a larger waistline. How is stress and belly fat connected? Stress can increase the secretion of a hormone called cortisol. This hormone increases the rate of fat accumulation by abdominal fat cells. Even among healthy individuals, repeated episodes of stress-related cortisol secretion is implicated in increased abdominal fat.
What Can Green Tea Do About It?
Green tea contains an unusual amino acid called L-theanine, which comprises up to 2.5% of the total dry weight of unfermented green tea leaves. This amino acid is absorbed efficiently and is able to enter the brain from the bloodstream. While in the brain, L-theanine releases relaxing physiologic effects. In this process, L-theanine may act to reduce stress perceptions, which in turn could have beneficial effects on abdominal fat formation. In one example, mice that were fed L-theanine accumulated less abdominal fat formation, and gained less weight. Green tea and green tea extracts that contain L-theanine can add to the support of healthy weight maintenance by supporting the body's stress response.
Joe Singleton has been in the vitamin and nutrition industry for over 20 years helping people understand the value of healthy aging. To read more, please check out the Purity Products website.
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