Oolong Tea: Benefits, Caffeine, Nutrition and Research

Oolong tea is a partially oxidized tea from the same plant as black and green tea, with flavors that run from light and floral to dark and roasted. Brewed plain it has almost no calories, and USDA FoodData Central lists it with a moderate amount of caffeine and a good share of the Daily Value for manganese. This guide covers what oolong is, the USDA numbers for oolong tea nutrition and caffeine, what the research on oolong tea benefits actually tested, and what to know about caffeine, iron and oxalate.

Peptide Labs does not sell tea. This article is general nutrition information, not medical advice.

What is oolong tea?

NCCIH, the NIH center for complementary health, explains that green, black and oolong teas all come from Camellia sinensis but are prepared differently: green tea is not fermented, black tea is fermented and oolong tea is partially fermented. In tea making, fermented means oxidized by the leaf’s own enzymes, not fermented by microbes. Because oxidation stops partway, oolongs sit between green and black teas in color and flavor.

A 2018 review of oolong in Critical Reviews in Food Science and Nutrition describes it as a traditional Chinese tea, especially popular in south China, and reports that more than 100 chemical compounds have been identified in it. Styles vary widely: some oolongs are only lightly oxidized and taste fresh and flowery, others are oxidized further and roasted for a toasty, fruity cup. Many are rolled into tight balls or long twisted leaves that open as they steep, and the same leaves are often brewed several times.

Oolong tea caffeine and nutrition (USDA)

USDA SR Legacy has one entry for brewed oolong, and unlike black tea it lists no serving size, only values per 100 grams. The table shows those per 100 gram values next to other brewed drinks, so the comparison is like for like.

Scaled to an 8 fluid ounce cup of 237 grams, the cup size USDA uses for brewed black tea, the USDA oolong values work out to about 38 milligrams of caffeine, 2 calories and 0.50 milligrams of manganese, roughly 22% of the Daily Value. On the same basis, USDA values give black tea about 47 milligrams of caffeine and brewed coffee about 95. A single USDA value cannot capture the wide range of oolong styles and brewing habits, especially when leaves are steeped several times, so read it as a rough guide.

For context, the FDA has cited 400 milligrams of caffeine a day as an amount not generally associated with negative effects for most adults, counting all sources, and stresses that sensitivity varies a lot. Our guide to caffeine limits explains that statement. Tea also contains a little theobromine, the compound most associated with cocoa, at about 2 milligrams per 100 grams in USDA data for both oolong and black tea.

Oolong tea benefits: what the research shows

Oolong is often marketed with slimming claims. The human evidence behind them is thin, and drinking oolong tea has not been shown to change body size. Here is what the studies actually measured.

• Energy expenditure study (2001, Journal of Nutrition): 12 men drank water, full-strength oolong, half-strength oolong or water with added caffeine, each for 3 days, in a randomized crossover design. Measured in a room calorimeter, 24-hour energy expenditure was 2.9% higher with full-strength oolong and 3.4% higher with caffeinated water than with water alone. Because caffeinated water did at least as well, caffeine likely explains much of the effect. The study lasted days, was tiny and did not measure body size.
• Large tea cohorts: the 2022 UK Biobank study of 498,043 adults, published in the Annals of Internal Medicine, linked higher tea intake with a modestly lower death rate from any cause, but black tea was the main type drunk, so it tells us little about oolong specifically. Observational studies cannot prove cause and effect.
• Lab chemistry: the 2018 review lists many polyphenols and other compounds in oolong. Lab and animal findings do not show an effect in people who drink the tea.

If you see an oolong product, capsule or extract promising slimming results, that is marketing, not evidence. Concentrated tea extracts are a different product with their own safety questions, covered in our green tea extract guide.

How oolong compares with black and other teas

Oolong is the middle ground. Compared with black tea, it is less oxidized, usually lighter in color and, in USDA data, a little lower in caffeine. Compared with unoxidized teas covered in our green tea guide and matcha guide, it is more oxidized and, in USDA data, a little higher in caffeine per cup. Herbal infusions such as chamomile are not made from the tea plant and are usually caffeine-free.

Iron, oxalate and other cautions

• Iron absorption: the NIH Office of Dietary Supplements notes that certain plant polyphenols reduce non-heme iron absorption. A 1999 study found black tea, coffee and herb teas all reduced iron absorption from a meal; oolong was not tested, but it carries the same kinds of tea polyphenols. If you have low iron, ask your clinician how tea fits your diet; see our guide to foods high in iron.
• Oxalate and kidney stones: tea contains oxalate, a compound studied in kidney stone research. A large 2013 cohort study linked tea drinking overall with fewer new kidney stones, but if you have had a stone, follow your clinician’s plan; our oxalates guide explains the background.
• Pregnancy and breastfeeding: the FDA advises talking to your health care provider about whether to limit caffeine if you are pregnant, trying to become pregnant or breastfeeding.
• Medicines, conditions and children: the FDA notes some conditions and medications raise caffeine sensitivity and suggests talking with a health care professional about a child’s or teen’s caffeine.
• Too much caffeine: signs the FDA lists include a fast heart rate, palpitations, trouble sleeping, jitters, anxiety, upset stomach, nausea and headache.
• Allergy: tea is not one of the nine major food allergens under US law; see an allergist for unclear reactions.

Frequently Asked Questions

Questions about a label? Contact us or read our Buyer’s Guide. Food comes first; follow the label and ask a healthcare provider before starting a supplement, especially if you take medicines, are pregnant or have a food allergy. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Last reviewed October 2026.

Related guides: Black Tea: Benefits, Caffeine, Nutrition and Research, Green Tea Benefits: What the Research Shows, Caffeine and Side Effects, Matcha Benefits: Caffeine, L-Theanine and What Studies Show.