A purple fruit and a steamed green leaf

The acai palm grows in the Amazon and bears round, dark purple fruit. The fruit has long been a food source for Indigenous people in the region.[1] Green tea comes from the same plant as black tea, and that plant was first grown in China thousands of years ago. Its leaves are steamed or pan-fried, then dried without fermenting.[2] That quick heat stops the leaf's own enzymes from changing its catechins. As a result, green tea keeps more of them than black or oolong tea.[3]

Both plants are rich in polyphenols. This big family of plant compounds gives many fruits and vegetables their red, blue and purple colors. Tea, cocoa and wine have plenty of them too.[4]

Your body changes these compounds a great deal after you swallow them. In a 2013 study in England, eight men took a common berry pigment tagged with a form of carbon that can be traced.[5] Its breakdown products peaked in their blood about 10 hours later. They lingered for up to two days.

This guide looks at the main compounds in green tea and acai and how your body handles them. It also covers what human studies have measured and the label advice that matters most for extracts. For the basics of oxidative stress, see our guide to oxidative stress.

What's in a cup of green tea

Three groups of compounds in green tea get most of the attention.

Catechins come first. There are four main ones, and EGCG (epigallocatechin gallate) makes up about 50% to 80% of the total.[4] Most green tea research focuses on EGCG.

Caffeine is second. A 12-ounce cup of green tea has about 37 milligrams. The same size cup of brewed coffee has 113 to 247 milligrams.[6] Amounts vary from one tea to the next.

Theanine is third. This amino acid makes up about 1% to 2% of the dry weight of tea leaves, and your body takes it in quickly.[7]

How an extract concentrates green tea

Brewing pulls some of these compounds into hot water. An extract goes further. Makers draw the compounds out of the leaves, clean them up and dry the result. That gives far more catechins per gram than a brewed cup.[3]

In Europe, green tea drinkers get about 90 to 300 milligrams of EGCG a day on average. Heavy tea drinkers get up to 866 milligrams. Supplements made with green tea catechins supply anywhere from 5 to 1,000 milligrams a day.[8]

Extracts can be standardized to a set level of catechins or EGCG, and some are decaffeinated. Our guides to standardized extracts and extract ratios explain how to read those numbers on a label.

What human studies of green tea have measured

Human research on green tea covers a lot of ground. Two lines of it fit a daily routine well.

The first is how much reaches your blood, and food makes a big difference. In one study, healthy adults took a single dose of a green tea extract that provided 800 milligrams of EGCG, 10 people per group. Taken while fasting, it gave peak levels of free EGCG more than five times higher than the same dose taken with food.[3] That finding sits behind the label advice in the next section.

The second is alertness. A 2014 review pooled 11 placebo-controlled trials of tea compounds.[9] The trials gave theanine or EGCG, alone or with caffeine. They measured alertness, attention and mood in the hours after a single dose.

Using green tea extract wisely

In 2020, an expert panel at USP (United States Pharmacopeia) that included FDA liaisons reviewed the safety of green tea extracts, including rare reports of liver problems.[3] Its practical advice centers on how you take an extract.

USP's quality standard for powdered decaffeinated green tea extract carries a label caution, and the 2020 review supported it.[3][10] In plain terms, it says:

• Don't take it on an empty stomach. Take it with food.
• Don't use it if you have a liver problem.
• Stop and talk with a health care practitioner if you notice signs of liver trouble. These include belly pain, dark urine, or yellowing of the skin or eyes.

Two more points are good to know. Green tea extract contains caffeine unless it has been decaffeinated. Large amounts of green tea may also make a medicine called nadolol less effective. If you take any prescription medicine, a quick pharmacist check is worth it.[2]

Acai: anthocyanins and what studies measure

Acai's color comes from anthocyanins. The same family of pigments shows up in blueberries, blackberries, raspberries and strawberries.[11] In one acai study, researchers measured its pigments as cyanidin-3-glucoside.[12] That's a common berry pigment and the same one used in the 2013 tracer study.[5]

Acai is traditionally eaten in Brazil, and it has become popular in other countries as a food and an ingredient.[12] Human studies of acai have looked at two things. One is how its pigments show up in the blood. The other is what happens to antioxidant markers in the blood after people eat or drink it. Two examples show how these studies work.

• In a 2008 study, 12 healthy adults came in after an overnight fast on four separate days.[12] Each time they had acai pulp, acai juice, applesauce or a drink with no antioxidants. Researchers sampled their blood over the next 12 hours. The acai pigments showed up in the blood and peaked about 2 hours later. The team also measured antioxidant capacity in the blood after each food.
• In a 2020 study, 30 healthy adults drank 200 milliliters (a little under a cup) of acai juice daily for 4 weeks.[13] In a separate 4-week period, they drank juice from juçara, a related palm. Before and after each juice period, researchers measured total antioxidant capacity in the blood and the activity of antioxidant enzymes such as catalase.

How your body takes in and changes polyphenols

A polyphenol you swallow is rarely the same compound that reaches your cells.

A review of 97 human studies found that uptake varies widely from one polyphenol to the next.[14] What turns up in the blood is mostly metabolites. Those are versions the gut and liver have already changed.

Your gut microbes do much of that changing. Most of the polyphenols you eat travel on to the large intestine, where bacteria break them into smaller pieces. In lab models of the gut, EGCG is split into a smaller catechin and gallic acid, then into still smaller acids. Anthocyanins break down into compounds such as protocatechuic acid.[4] Many of these smaller pieces are absorbed and carried around the body.

That helps explain the 2013 tracer study. The tagged pigment turned out to be more available to the body than earlier studies had suggested.[5] The researchers identified many of the tagged compounds in blood and urine as breakdown products, such as phenolic acids.

The link runs both ways. Polyphenols can also shape which microbes thrive in your gut. Because everyone's gut microbes differ, two people can respond to the same food in different ways.[4]

Scientists study polyphenols in two settings. In a test tube, they take on free radicals directly. Inside the body, researchers are also exploring how they work through cell signaling. That's the system of chemical messages cells use to adjust what they do.[11]

Food and extracts: how they fit together

Brewed green tea has a long history as an everyday drink. Aside from water, tea is the most widely consumed drink in the world.[7] Berries, tea, cocoa and many vegetables add polyphenols to your plate every day.[4] One easy pairing is a cup of green tea at breakfast with a handful of berries stirred into oatmeal or yogurt.

An extract does a different job. It packs a plant's compounds into a capsule you can take at the same time every day. That is also why an extract comes with its own label directions.

Your plate and your cup supply these compounds every day, and an extract adds a concentrated, steady amount alongside them. For a wider look at the plants in this series, see our guide to what's inside a detox supplement.

Where green tea extract and acai fit in a daily routine

Formulas with tea-based botanicals often fit the morning. Green tea extract carries caffeine unless it has been decaffeinated, so a morning slot lets you count it alongside your usual tea or coffee.

Before you add one, turn the bottle around. Here is what you may see:

• green tea extract listed with its own amount, or inside a proprietary blend with a total weight, a common and legal format
• whether the extract is decaffeinated, and sometimes a caffeine amount per serving
• any other caffeine source in the formula
• the form of acai, such as fruit powder or extract
• directions that give the serving and the time of day

Our guide to reading a detox supplement label walks through each part of the panel.

Picture the kettle warming, a bowl of berries on the table and a glass of water beside your breakfast plate. Taken at the same point each morning, an extract becomes one steady step each day, alongside the tea you drink and the colorful food you eat.

Frequently asked questions

Is drinking green tea the same as taking green tea extract?

They share the same compounds in different forms. Tea drinkers in Europe average about 90 to 300 milligrams of EGCG a day from tea. Supplements range from 5 to 1,000 milligrams.[8] An extract comes in a set serving with its own label directions.

What is theanine?

Theanine is an amino acid found in tea leaves, where it makes up about 1% to 2% of the dry weight. Your body takes it in quickly from the small intestine, and nearly all of it is absorbed.[7] Studies of tea compounds often test it alongside caffeine.[9]

How much caffeine is in green tea?

About 37 milligrams in a 12-ounce cup. That's roughly a third or less of what the same cup of coffee holds.[6] Green tea extracts contain caffeine too, unless they're decaffeinated.

Is acai better than other berries?

Acai is one of many fruits rich in anthocyanins, along with blueberries, blackberries, raspberries and strawberries.[11] Enjoying a mix of colorful fruit, acai included, is a sensible everyday goal.

Why might two people respond differently to the same plant compounds?

Gut microbes do much of the work of breaking polyphenols down, and everyone's mix of microbes is different.[4]