Oolong Tea

Oolong tea comes from the same plant as green and black tea, Camellia sinensis, but its leaves are only partly oxidised, which places it between the two. Partial oxidation turns some of the leaf's catechins into polymerized polyphenols, which have been studied for their effect on dietary fat absorption. A cup also carries caffeine. Traditional Chinese belief holds that oolong helps control body weight, and it is one of the few teas tested directly in human metabolism studies. The results are real but modest.

Benefits of Oolong Tea

Studied for a modest rise in daily energy use

Studied for increased fat burning

May reduce absorption of dietary fat

Linked to lower risk of high blood pressure

Studied for blood sugar support in type 2 diabetes

A natural source of manganese

Key Nutrients

Brewed tea is not a significant source of most vitamins and minerals. Manganese is the exception — published analyses find it in meaningful amounts.

Manganese: Supports antioxidant enzymes, bone formation, and energy metabolism. Ti Kuan Yin oolong was among the teas analysed.

Good to know: tea's polyphenols reduce absorption of iron from plant foods. If iron is a concern, enjoy your tea an hour or more after meals.

Oolong Tea's Bioactive Components

Polymerized polyphenols: Formed during oolong's partial oxidation. Oolong enriched with these polyphenols increased the fat excreted from a high-fat diet.

Catechins: The leaf's original polyphenols, partly preserved because oolong is only partly oxidised.

Caffeine: The main driver of oolong's effect on energy use; caffeine alone produced a similar rise in the key metabolism study.

Why Drink Oolong Tea in Your Tea Blends?

Oolong gives a blend a smooth, floral base and a steady lift, with honest, measured human research behind it. Here's why it earns its place:

Supports an Active Metabolism: Men drinking oolong brewed from 15 g of leaf a day (five strong servings) used 2.9% more energy over 24 hours. Caffeinated water alone produced a similar rise, so caffeine does much of the work.

Supports Fat Burning: Fat oxidation was 12% higher on full-strength oolong than on water. A later trial found oolong increased fat burning without changing total energy use or disturbing sleep.

Helps Reduce Dietary Fat Absorption: On a high-fat diet, oolong enriched with extra polyphenols roughly doubled the fat excreted compared with placebo.

Linked to Healthy Blood Pressure: Taiwanese adults who drank 120 mL or more of green or oolong tea a day for a year had a significantly lower risk of developing high blood pressure.

Studied for Blood Sugar Support: In adults with type 2 diabetes taking medication, 30 days of oolong lowered blood sugar compared with water. The evidence is mixed: a Japanese cohort linked very high oolong intake to higher diabetes risk.

Contains caffeine. The metabolism studies used large daily amounts; one cup delivers a much smaller effect.

Scientific Evidence

Energy use and fat burning

Randomized crossover trial: 12 men had water, full-strength oolong (15 g leaf a day), half-strength oolong, or caffeinated water. Energy use rose 2.9% with oolong and 3.4% with caffeinated water; fat oxidation was 12% higher with oolong.

Oolong tea increases metabolic rate and fat oxidation in men — Rumpler W. et al. Journal of Nutrition, 2001; 131(11): 2848-2852.

"fat oxidation was significantly higher (12%) when subjects consumed the full-strength tea"

Fat burning without sleep disruption

Randomized, double-blind, placebo-controlled crossover trial: daily oolong tea and caffeine both increased fat burning, without changing total energy use or sleep architecture.

Subacute Ingestion of Caffeine and Oolong Tea Increases Fat Oxidation without Affecting Energy Expenditure and Sleep Architecture — Nutrients, 2020; 12(12): 3671.

"Increases Fat Oxidation without Affecting Energy Expenditure and Sleep Architecture"

Dietary fat absorption

Human crossover study on a high-fat diet: polyphenol-enriched oolong raised fat excreted in stools to 19.3 g over 3 days, versus 9.4 g on placebo. This used oolong enriched with extra polyphenols, not standard oolong.

Polyphenol-enriched oolong tea increases fecal lipid excretion — Hsu T.F. et al. European Journal of Clinical Nutrition, 2006.

"polyphenol-enriched oolong tea could increase lipid excretion into feces"

Blood pressure

Cohort study of 1,507 Taiwanese adults: drinking 120 mL or more of moderate-strength green or oolong tea a day for at least a year was linked to a significantly lower risk of developing hypertension.

The protective effect of habitual tea consumption on hypertension — Yang Y.C. et al. Archives of Internal Medicine, 2004; 164(14): 1534-1540.

"significantly reduces the risk of developing hypertension in the Chinese population"

Blood sugar in type 2 diabetes

Randomized crossover trial: 20 adults with type 2 diabetes on medication drank 1.5 L of oolong or water a day for 30 days each. Plasma glucose fell from about 229 to 162 mg/dL with oolong; water produced no change. Conducted with Suntory, an oolong producer.

Antihyperglycemic Effect of Oolong Tea in Type 2 Diabetes — Hosoda K. et al. Diabetes Care, 2003; 26(6): 1714-1718.

"Oolong tea may be an effective adjunct to oral hypoglycemic agents"

Blood sugar (counter-evidence)

Prospective cohort of Japanese male workers: high oolong intake predicted a higher future risk of diabetes. Observational, so it shows a link, not cause.

High oolong tea consumption predicts future risk of diabetes among Japanese male workers — Hayashino Y. et al. Diabetes Care, 2012; 35: 226-232.

"High oolong tea consumption predicts future risk of diabetes among Japanese male workers"