G

Green tea has a decades-old reputation

as a fat-burning, cancer-fighting elixir in a cup, in part

because of its role in traditional—and healthful—Asian

diets, but also because of its catechins, a group of poly-

phenols largely found in tea, cocoa, and berries. Search

for “tea and health” on PubMed and you’ll find thou-

sands of studies, some high quality and based on strong

evidence but many not.^1 Unfortunately, results of many

laboratory studies have been unreasonably extrapo-

lated to human health, with the resulting weak claims

picked up and spread through popular media.

If you were to trace the phytochemical “family tree,”

catechins are types of flavanols, which are types of

flavonoids, which are types of polyphenols. The main

catechins are catechin, epicatechin, epigallocatechin

(EGC), epicatechin gallate (ECG), and epigallocatechin

gallate (EGCG). High concentrations of catechins can be

found in red wine, broad beans, black grapes, apricots,

and strawberries. Epicatechin concentrations are high

in apples, blackberries, broad beans, cherries, black

grapes, pears, raspberries, and cocoa/chocolate.

However, one of the richest, best-studied, and most

attention-grabbing sources of catechins is the Camellia

sinensis plant, from which green, black, white, and

oolong teas derive. EGC, ECG, and EGCG are found in

high concentrations in oolong, black, and green teas,

but particularly in green tea because the leaves are

dried and steamed instead of fermented (fermentation

converts some of the catechins into more complex

theaflavins and other flavonoids).1-

Traditional Medicine Goes Modern

C sinensis historically has been used for medicinal

purposes. EGCG accounts for about two-thirds of the

catechins in green tea and thus has attracted the most

attention in the scientific community.2,

Catechins, especially EGCG, have strong antioxidant

activity and are notable for their ability to scavenge

free radicals.1,2 These antioxidant capabilities are

significant, because inflammation and oxidative stress—

the imbalance between pro-oxidants and antioxidants

that results in free radical damage—are considered

underlying causes of many chronic diseases, including

CVD, type 2 diabetes, neurodegenerative diseases, and

c a n c e r.^4 Catechins also can bond to proteins, lipids, and

nucleic acids, and their ability to bind to proteins may be

an important mechanism behind their anticancer and

other health-promoting properties.1,5 It’s thought that

the benefits of tea primarily come from its catechins, but

also from its smaller amounts of quercetin and other

polyphenols—as well as its alkaloids, such as caffeine

and theobromine.^1 So, despite the hype around EGCG, it’s

not all about the EGCG.

“That’s a traditional approach in pharmacology, to

study a pure compound,” says Chung Yang, PhD, a dis-

tinguished professor at Rutgers University in New

Brunswick, New Jersey, who studies the pharmacology

and other aspects of green tea and health. He agrees

that not all of green tea’s benefits are from the EGCG. “I

think it’s probably an additive effect of not just the cat-

echins but the other constituents,” Yang says, pointing

out that caffeine may aid in weight management and

that tea contains theanine, an amino acid that research

suggests may promote a relaxed but alert mental state

and confer other health benefits.^6

Nagi Kumar, PhD, RD, FADA, director of cancer

chemoprevention at Moffitt Cancer Center & Research

Institute in Tampa, Florida, says that, although many

clinical trials have emphasized the efficacy of EGCG,

they all used a catechin supplement that contained

all the catechins present naturally in green tea. “This

is because in vitro and in vivo studies have clearly

Green Tea Catechıns

By Carrie Dennett, MPH, RDN, CD

18 today’s dietitian august 2019