Pu-erh Tea—More of It May Mean Less of You

Fighting Fat with Pu-erh Tea
The composition of this exotic, aged tea gives it a special
ability to help prevent weight gain
By Will Block

besity is not for sissies. It’s tough being obese, and the long-term prospects are not good. The word conjures up images of the fat we can see and feel: the pudgy cheeks, the flabby arms, the stout legs, and, especially, the midriff bulge—those pinchable inches of fat that can make our bellies look “like a bowlful of jelly.” But leave the jelly-belly to St. Nick. For the rest of us, the fat it contains is the most harmful to our health. It’s not so much the fat we can see and feel there, but the hidden fat beneath—called visceral fat—that we can’t see or feel.

Excessive fat surrounding the liver, pancreas, kidneys, and other internal organs has been linked to high levels of fat, glucose, and insulin in the blood, and those are reliable predictors of diabetes, heart disease, and other chronic conditions—the unintended and potentially fatal consequences of allowing ourselves to gain too many pounds. Obesity is also associated with increased risks for various cancers, including those of the liver, colon, breast, ovary, and prostate.

It’s Not How Much You Eat, but What You Eat . . .

To reduce our visceral fat, we can reduce our overall fat load through diet and exercise, the twin pillars of good health. We all know what exercise is, but diet is not as easy to define, because there are so many different approaches to this unwelcome subject. The important thing to remember is that diet need not mean a restriction on how much you eat (although that may well be a factor), but rather on what you eat.

Substituting more nutritious foods for excessively fatty or sugary foods is a no-brainer, but another good strategy is to avoid foods with a high glycemic index, concentrating instead on those with a low glycemic index. It’s also possible to reduce the average glycemic index of your meals by using selectively bred beta-glucan-rich barley as a cereal, a beverage, or a substitute for conventional carbohydrates, such as rice and potatoes. By doing so, you will avoid the “spikes” in blood sugar levels that are not only harmful by themselves (they induce the formation of advanced glycation end products, aptly abbreviated AGEs) but that also unleash a chain of bad physiological consequences, including undue weight gain.

. . . And Drink

Furthermore, there are nutritional supplements that can, in conjunction with diet and exercise, help you shed even more pounds, or prevent them from being put on in the first place—especially if the diet in question is a low-glycemic-index diet. One such supplement is tea.

Tea, a supplement? Well, yes, it can be (powdered green tea extracts in capsule form are especially beneficial), but tea as a beverage is delightful and happens to be among the most healthful foods known to man, despite having no protein, carbohydrate, or fat content (hence, zero calories). It’s all about tea’s content of flavonoids, a large class of naturally occurring antioxidant compounds in the much larger class called polyphenols.

Pu-erh—With Age Comes Quality

Last month we featured an unusual kind of tea called Pu-erh (pronounced poo·air), a name that designates both a regional tea varietal and a special processing method. (See “Pu-erh Tea—Exotic, Aged, and Anti-Fat” in the June 2007 issue). For those who haven’t read the article, we’ll summarize the basics here.

Pu-erh is a broadleaf tea varietal (Camellia sinensis var. assamica) that comes from Yunnan province in southwestern China, where there is a town called Pu’er. Virtually all true teas fall into one of the four major kinds of tea—white or green (both unfermented), oolong (partially fermented), and black (fully fermented). Pu-erh is different: although it’s made as a green tea, it’s much better known for being made as a fully fermented tea that’s analogous to black tea. Although the result is a black type of tea, the processing method used is unique to Pu-erh, and the tea is unlike black tea in some ways. Actually, two processing methods are used, one of ancient origin and one of recent invention. Thus there are really three kinds of Pu-erh tea:

  1. Green Pu-erh (aka raw or uncooked Pu-erh). As with any other green tea, the freshly picked leaves are heated briefly to inactivate the tea enzymes that cause fermentation; this prevents the tea from becoming an oolong tea or a black tea, which are made by the fermentation of leaves that have not been heated. Green Pu-erh is sold as loose leaves for consumption immediately or after a brief aging period.

  2. Aged raw Pu-erh (aka secondary oxidation/ fermentation Pu-erh). More often, the heated green tea leaves described above are lightly steamed and compressed into cakes of various sizes and shapes, to be aged anywhere from a few years to a few decades before consumption. During the aging period, oxidative and microbial processes slowly ferment the tea, producing a strongly fermented black-type tea (but it’s not called black). These processes alter the tea’s chemical composition in ways that improve the tea with age; they also confer on the tea some remarkable health benefits, particularly in the area of fat reduction. Aged raw Pu-erh is the most highly prized of all teas by connoisseurs, who believe that the longer the aging, the better the tea; individual cakes weighing about a pound can fetch hundreds or even thousands of dollars.

  3. Black Pu-erh (aka ripened, fermented, or cooked Pu-erh). This much more affordable tea is called black, although it too is not made by the traditional black-tea process. Instead, the heated green tea leaves are subjected to an artificial aging process, invented in China in 1972, that resembles composting; it induces microbial fermentation to the black state much more quickly and efficiently than in aged raw Pu-erh. The fermented leaves are sold loose or are compressed into cakes for further aging for a few years. Although it does not match aged raw Pu-erh in quality, black Pu-erh is still considered a good tea.

Pu-Erh Reduces Rat Fat

Plastic model of 1 lb of excess fat. Imagine multiplying it by . . . ?
In 1986, Japanese researchers published a study on the effects of Pu-erh tea and conventional green tea (in leaf form) on lipid metabolism in rats whose diet contained 1% cholesterol by weight.1 (Lipids are fats and various other fatty substances, such as cholesterol.) Two samples of Pu-erh, aged for 2 years or 20 years, were used. The 20-year-old tea could not have been black Pu-erh, because that kind had been in existence for only 14 years; thus it had to have been aged raw Pu-erh.

Neither the green tea nor the Pu-erh tea had any significant effect on the rats’ body weight, but the Pu-erh group had a significant reduction of adipose tissue (body fat), both in absolute terms and as a percentage of body weight; green tea had no such effect. Furthermore, the plasma levels of triglycerides (fat molecules) were reduced in the Pu-erh group but not in the green tea group. (There were no appreciable differences between the 2-year-old and 20-year-old Pu-erh teas in any measure.) On the other hand, the plasma levels of free fatty acids (the principal constituents of triglycerides) and cholesterol were not changed in any group by the end of the study.

Fatty Acid Synthase—A Key Step on the Way to Fat

Schematic diagram of fatty acid synthase (FAS), a large, complex enzyme consisting of two identical subunits joined like Siamese twins. Each half contains seven proteins as functional domains that catalyze different biochemical reactions involved in the synthesis of palmitic acid. The coiled ribbons represent polypeptide chains.
In the last few years, a number of papers have been published on the fat-fighting and other properties of teas, including Pu-erh tea; some of these have focused on the teas’ ability to inhibit the action of fatty acid synthase (FAS), an enzyme complex that plays a key role in our bodies’ production of fatty acids, the precursors of fat molecules.2,3 Because FAS is produced mainly in the liver and in adipose (fat) tissue, that is where fatty acids are produced—as is fat itself, ultimately.

What FAS actually does is catalyze the production of a particular fatty acid, palmitic acid, from compounds called acetyl-coenzyme A and malonyl-coenzyme A, which are derived from the foods we eat via complex chemical reaction sequences. Other fatty acids are then produced from palmitic acid by the catalytic action of other enzymes.

Our bodies use these fatty acids (along with those from the digestion of fat in our food) in three main ways: (1) some are used for the synthesis of other compounds, such as the phospholipids in our cell membranes; (2) some are used as cellular fuel by various tissues; and (3) some are converted, by the action of enzymes called phosphatases, to fat molecules (triglycerides) for energy storage. Where the balance lies among these three uses depends on many factors that interact in complex ways.

FAS Is an Inviting Target

FAS levels are regulated by diet and hormones and are found to be elevated in a wide variety of human cancers, including cancer of the prostate, breast, endometrium (the uterine lining), ovary, lung, colon, stomach, and thyroid. Because of FAS’s connection with both obesity and cancer, it presents an inviting target for biochemical intervention, in the same way that one of the enzymes involved in the biosynthesis of cholesterol is the target of statin drugs, which restrict the overall process by inhibiting that enzyme. (It’s interesting to note, by the way, that trace amounts of natural lovastatin have been found in some samples of Pu-erh tea.4)

In 1972 it was discovered that the synthetic antibiotic cerulenin was a FAS inhibitor; this led, in the 1990s, to investigations of FAS inhibition as a means of cancer chemotherapy.5 Only in this century, however, have scientists been looking for agents that could inhibit FAS—and, therefore, lipogenesis (the production of fat)—for the purpose of combating obesity. One such agent of current interest is Pu-erh tea, which contains chemical compounds not found in conventional teas. Let’s digress for a moment to talk about these compounds.

What Tea Is Made of

White tea and green tea are rich in a type of flavonoid called catechins. The catechins—especially one called epigallocatechin gallate (EGCG)—are noted for their protective effects against heart disease and cancer. In conjunction with two other tea components, caffeine and the rare amino acid theanine, they are also credited with antiobesity and antilipidemic (lipid-reducing) actions.*

*One often hears that adding milk to tea, as the British like to do, effectively destroys the tea’s health benefits, because the catechins bind to milk proteins and are thus inactivated. That’s true in cell-culture experiments, but not in human beings, because our digestive systems break down the proteins and set the catechins free.

When tea leaves are allowed to ferment to black tea, however, most of the catechins are destroyed in chemical reactions that convert them to other compounds, mainly theaflavins and thearubigins (which are actually catechin polymers). These flavonoids have considerable biological activity of their own, but they’re not as potent as the catechins.

†For more on the health benefits of black tea, see “Theanine May Help You Fight Off Disease” (July 2003) and “Tea Extract Helps Reduce Cholesterol Levels” (December 2003).

Most Pu-erh tea, being of a black nature, has almost no catechin content—it has even less than conventional black tea—which makes it different from green teas (including, of course, green Pu-erh). It also, however, has almost no theaflavins or thearubigins, which makes it different from conventional black teas.6 Pu-erh does, however, have caffeine and theanine—which are not destroyed in the fermentation process—as well as a variety of compounds not found in conventional teas of any color.7 These compounds are formed during the aging process by the actions of various fungi (especially one called Aspergillus niger), and scientists believe they are probably responsible for some of Pu-erh’s health benefits. Which brings us back to the inhibition of fatty acid synthase and, therefore, of lipogenesis.

Pu-erh Reduces Weight Gain and Fat, Perhaps by Inhibiting FAS

In Taiwan, researchers studied the effects of feeding four kinds of tea—green, oolong, black, and Pu-erh (of unspecified type, but it was certainly either aged raw or black)—to young rats.8 They found that all four teas suppressed the test rats’ body-weight gains compared with those of the control rats; in descending order of efficacy, the teas were Pu-erh, oolong, black, and green. Surprisingly, despite the weight losses, there were no significant differences in total food intake among the test and control groups of rats. In addition, Pu-erh and oolong significantly lowered triglyceride levels, whereas green and black did not. All four lowered total cholesterol levels, and here Pu-erh was the least effective.

‡The carelessly prepared paper was marred by a number of substantive errors and contradictions.

Based on these and other findings, the researchers surmised that the teas’ action was probably due to an inhibition of FAS, mainly by compounds resulting from fermentation processes. To pursue this idea, they investigated the teas’ actions on FAS in cultures of human liver cancer cells.9 They found that all four teas were active in inhibiting FAS, but Pu-erh was the most effective, probably owing to the compounds that are unique to that type of tea. The results of this study are in accord with numerous others showing that polyphenols of many kinds, including flavonoids and nonflavonoids, are FAS inhibitors and thus have potential for fighting both obesity and cancer.2

The Grand Old Man of Fat

Fat—the good, the bad, and the ugly—has always been a part of us, but it was not until 1809 that we began to understand what fat really is. In that year, a young French chemist named Michel Eugène Chevreul opened a new branch of chemistry when he discovered that the principal constituents of fat molecules are organic acids that came to be known as . . . fatty acids. In studying the chemistry of soap, which is ordinarily produced from fat, Chevreul isolated palmitic acid, stearic acid, and oleic acid, the three most common and important constituents of fats and oils of animal or vegetable origin. (Oils, by the way, are just fats that are liquid at room temperature.)

Quite apart from the important roles they play in human nutrition and metabolism, fatty acids proved to have commercial potential in nineteenth-century Europe. In 1825, Chevreul and the great French chemist Joseph Louis Gay-Lussac obtained a patent on the manufacture of candles from fatty acids. It sounds quaint to us now, but it was a big deal back then: the new candles were harder and better-looking than the old candles made from tallow (animal fat); they gave brighter light; they needed less care while burning; and they didn’t smell as bad. They were a huge success, and Chevreul was elected to the Academy of Sciences the very next year.

Chevreul’s reputation was based on far more than soap and candles, however. In 1815, he had isolated sugar from the urine of a diabetic patient and showed that it was identical to grape sugar, or dextrose. Dextrose is a synonym for glucose, which we now know as the body’s principal source of the chemical energy needed to drive all life processes. Chevreul’s discovery provided the first clue that diabetes, a disease known since ancient times, was a disorder of sugar metabolism. The primary risk factor for this disease is obesity, the accumulation of excess fat.

The precursor condition to diabetes is insulin resistance, which is age-related. Here again, there is a Chevreul connection, for he was a pioneer in gerontology, the study of the aging process in health and disease. In his nineties, he studied the psychological effects of old age, a condition that seems to have had little impact on his own energy and productivity—he published his last scientific paper at the age of 102, just one year before death finally claimed him, in 1889. (Chevreul had “chosen” his parents well, by the way: they both lived into their nineties.)

Much earlier in his career, Chevreul’s knowledge of dye chemistry had landed him a job as the director of dyeing for a famous French tapestry firm, where he became interested in the psychology of color perception. His efforts to establish standards in this field wound up having a strong influence on the impressionist school of painting, which originated in France in the 1870s. And in the 1850s, he spent time exposing the fakery involved in spiritualism, which had become quite a fad in Europe and the United States.

Chevreul was truly a blessed man—a distinguished scientist who lived a long and productive life, with many honors. His 100th birthday was celebrated with a torchlight parade through the streets of Paris, and his funeral three years later in the Cathedral of Notre Dame drew thousands of mourners.

Pu-erh Shows Strong Antioxidant Activity

It has been said that black tea, generally speaking, has only about one-sixth the antioxidant power of green tea, owing mainly to the former’s low levels of catechins. That may be true in some cases, but not all—it depends on what kind of antioxidant activity you’re measuring, and how you’re measuring it. As evidence of this, Taiwanese researchers recently published a laboratory study using four types of tea: green, oolong, black, and Pu-erh (the last of these was probably black Pu-erh, although this was not specified).10

In the particular experiments they were conducting, the researchers found that all four teas had nearly identical levels of antioxidant activity. That’s remarkable, considering the fact that the polyphenolic compositions of these teas are dramatically different. It suggests that, as the strongly antioxidant catechins in green tea are destroyed by the fermentation reactions leading to oolong, black, and Pu-erh teas, there is a compensatory gain in antioxidant activity from the new compounds produced.

Thus it appears that all teas can provide health benefits deriving from antioxidant activity—as is suggested, in fact, by much scientific evidence—but the particular benefits will depend on various factors, including the kind of tea in question.6

The SARS Connection

Among the unexpected potential health benefits of tea is its apparent ability (in the laboratory) to counteract the virus responsible for SARS (severe acute respiratory syndrome), the disease that became big news in November 2002 when the first, and so far only, major outbreak occurred in China and quickly spread around the world, only to fizzle out in 8 months. The virus produces a protein-destroying enzyme called 3CLPro, the inhibition of which would be a means of attacking the disease.

Researchers in Taiwan discovered that extracts of Pu-erh and black teas, but not green or oolong teas, were effective inhibitors of this deleterious enzyme.11 They identified three compounds found in fully fermented teas—tannic acid, theaflavin-3’-gallate, and theaflavin-3,3’-digallate—as being particularly effective 3CLPro inhibitors. Even so, let’s hope that SARS does not arise again.

Got tea?
Tea for Toughness

At the beginning of this article, we said that obesity is not for sissies. Considering that Pu-erh tea may help combat the fat that leads to obesity, it’s unfortunate that tea is viewed, in some quarters of our coffee-oriented society, as a beverage for sissies. Those folks probably haven’t tried earthy-tasting Pu-erh tea or considered the prospect that Pu-erh might help them slim down and tighten up, making them even tougher than they already are. Pu-erh—not for sissies!


  1. Sano M, Takenaka Y, Kojima R, Saito SI, Tomita I, Katou M, Shibuya S. Effects of Pu-erh tea on lipid metabolism in rats. Chem Pharm Bull 1986;34:221-8.
  2. Tian WX. Inhibition of fatty acid synthase by polyphenols. Curr Med Chem 2006;13:967-77.
  3. Lin JK, Lin-Shiau SY. Mechanisms of hypolipidemic and anti-obesity effects of tea and tea polyphenols. Mol Nutr Food Res 2006;50:211-7.
  4. Yang DJ, Hwang LS. Study on the conversion of three natural statins from lactone forms to their corresponding hydroxy acid forms and their determination in Pu-erh tea. J Chromatogr A 2006;1119:277-84.
  5. Pizer ES, Wood FD, Pasternack GR, Kuhajda FP. Fatty acid synthase (FAS): a target for cytotoxic antimetabolites in HL60 promyelocytic leukemia cells. Cancer Res 1996;56:745-51.
  6. Jie G, Lin Z, Zhang L, Lu H, He P, Zhao B. Free radical scavenging effect of Pu-erh tea extracts and their protective effect on oxidative damage in human fibroblast cells. J Agric Food Chem 2006;54:8058-64.
  7. Zhou ZH, Zhang YJ, Xu M, Yang CR. Puerins A and B, two new 8-C substituted flavan-3-ols from Pu-er tea. J Agric Food Chem 2005;53:8614-7.
  8. Kuo KL, Weng MS, Chiang CT, Tsai YJ, Lin-Shiau SY, Lin JK. Comparative studies on the hypolipidemic and growth suppressive effects of oolong, black, Pu-erh, and green tea leaves in rats. J Agric Food Chem 2005;53:480-9.
  9. Chiang CT, Weng MS, Lin-Shiau SY, Kuo KL, Tsai YJ, Lin JK. Pu-erh tea supplementation suppresses fatty acid synthase expression in the rat liver through downregulating Akt and JNK signalings as demonstrated in human hepatoma HepG2 cells. Oncol Res 2005;16:119-28.
  10. Duh PD, Yen GC, Yen WJ, Wang BS, Chang LW. Effects of Pu-erh tea on oxidative damage and nitric oxide scavenging. J Agric Food Chem 2004; 52:8169-76.
  11. Chen CN, Lin CPC, Huang KK, Chen WC, Hsieh HP, Liang PH, Hsu JTA. Inhibition of SARS-CoV 3C-like protease activity by theaflavin-3,3’-digallate (TF3). Evid Based Complement Alternat Med 2005;2:209-15.

Will Block is the publisher and editorial director of Life Enhancement magazine.

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