Oolong tea, a traditional beverage consumed in China and Taiwan, accounts for a small percentage of tea consumption worldwide, yet it possesses a variety of potential health benefits. As with green and black teas, oolong tea comes from the Camellia sinensis plant, with differences arising during harvesting and processing. Oolong tea is partially fermented, placing it between green tea (unoxidized) and black tea (fully fermented). This unique processing influences its antioxidant profile, falling between green tea's catechins and black tea's theaflavins and thearubigins.
Nutritional Profile of Oolong Tea
Oolong tea contains a moderate amount of caffeine, ranging from 10 to 60 milligrams per 8-ounce cup, which is less than coffee's 70 to 130 mg. Unsweetened brewed tea is a zero-calorie beverage, devoid of fat, carbohydrates, and protein. Furthermore, oolong tea provides essential minerals and vitamins, including manganese, potassium, magnesium, niacin, and sodium. It also contains fluoride, potentially contributing to dental health. A typical cup of brewed oolong tea (2 grams of leaves in 8 ounces of water) contains approximately 2.4 calories, 0 grams of protein and fat, 0.36 grams of carbohydrates, 0 grams of fiber and sugar.
Oolong Tea and Weight Management: Scientific Studies
Several studies have explored the potential of oolong tea in promoting weight loss and managing obesity.
Animal Studies
One study on mice fed a high-fat, high-sugar diet demonstrated that oolong tea extract reduced abdominal fat gain compared to a control group. Green tea and black tea extracts also showed similar effects. Notably, the mice receiving green tea extract consumed fewer calories.
Human Studies
- Body Weight Reduction: A study involving overweight and obese Chinese adults examined the impact of oolong tea consumption on body weight. Participants consumed 300 mL of oolong tea four times daily. After six weeks, over half of the participants experienced a weight loss exceeding 1 kilogram.
- Fat Metabolism: Research indicates that oolong tea may decrease body fat content and boost metabolism, potentially reducing obesity risk and supporting weight loss. Studies suggest oolong tea can stimulate fat burning and increase calorie expenditure by up to 3.4%.
- Lipid Metabolism Improvement: A study involving 102 diet-induced overweight or obese individuals who ingested 8 grams of oolong tea daily for six weeks revealed promising results. 70% of severely obese subjects showed a weight loss of more than 1 kg, with 22% losing over 3 kg. Similarly, 64% of obese and 66% of overweight subjects lost more than 1 kg. Subcutaneous fat content decreased in 12% of the subjects. The study also found that plasma triglyceride (TG) and total cholesterol (TC) levels in subjects with hyperlipidemia significantly decreased after oolong tea ingestion.
Mechanisms of Action
Oolong tea's potential weight loss benefits are attributed to several mechanisms:
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- Improved Lipid Metabolism: Oolong tea could decrease body fat content and reduce body weight through improving lipid metabolism.
- Enhanced Lipolysis: Caffeine, found in oolong tea, enhances noradrenaline-induced lipolysis in adipose tissue.
- Pancreatic Lipase Inhibition: Some substances in oolong tea inhibit pancreatic lipase activity.
- Polyphenols: The polyphenols in oolong tea lower blood sugar levels and reduce insulin resistance. They also activate an enzyme that breaks down triglycerides, reducing the risk of heart disease.
Study on High-Fat Diet-Induced Obese Mice
- Experimental Design: C57BL/6 mice were divided into three groups: normal diet (ND), high-fat diet (HFD), and high-fat diet with oolong tea supplementation (HFD + OT). The study lasted for 8 weeks.
- Key Findings:
- OT supplementation inhibited HFD-induced overweight from week 4 onward and lowered the total weight gain in HFD-fed mice.
- OT suppressed HFD-induced higher levels of serum lipid.
- OT intervention mitigated the increased weight of perirenal fat and epididymal fat.
- OT treatment significantly reversed the mRNA expressions of Srebf1 and Pgc1a and suppressed the mRNA expression of Leptin, Ppara, Il-6, and Il-1b.
- OT intervention remarkably lowered liver weight in mice on HFD.
- OT intervention improved HFD-induced indistinct cell boundaries, denaturation, and irregular damaged cells with cytoplasmic vacuolation.
- OT supplementation significantly upregulated the mRNA expression of Hsl, Ppara, and Lxra in comparison to the HFD group.
- OT intervention mitigated changes in fasting blood glucose levels.
- OT could inhibit HFD-induced significant increment in serum LPS levels.
- OT could strikingly suppress inflammatory infiltration including aggregated lymphocytes, absence of neutrophils and wheel-like plasma cells in the crypt lumen, and abnormal epithelium characterized by lower levels of goblet cells and mucin depletion.
- OT could significantly prevent HFD-caused increased levels of TNF-α and IL-6.
Oolong Tea and Gut Microbiota
Emerging evidence suggests that gut microbiota plays a role in obesity-related diseases. A study involving 16S ribosomal RNA (rRNA) sequencing investigated the impact of oolong tea on the gut microbiota composition in mice. The results indicated that oolong tea could modulate gut microbial profile, which may contribute to its anti-obesity effects.
Additional Health Benefits of Oolong Tea
Beyond weight management, oolong tea offers several other potential health benefits:
- Heart Health: Research suggests oolong tea can lower cholesterol levels and reduce the risk of heart disease.
- Diabetes Prevention: Studies indicate that the polyphenols in oolong tea may lower blood sugar levels and reduce insulin resistance, both risk factors for diabetes.
- Dental Health: Oolong tea contains fluoride, which may help prevent cavities.
- Cognitive Support: Oolong tea is rich in L-theanine, an amino acid associated with improved brain activity, better sleep quality, and reduced stress and anxiety. Its antioxidants may also protect against neurodegenerative diseases.
Considerations and Recommendations
While oolong tea appears to offer several health benefits, it's essential to consider the following:
- Caffeine Content: As oolong tea contains caffeine, individuals sensitive to caffeine should limit their intake to avoid potential side effects such as headaches, irritability, increased heart rate, and insomnia. Experts recommend not exceeding 400 milligrams of caffeine per day.
- Iron Absorption: Tea can decrease the amount of iron absorbed from plant foods. It may be better to drink tea outside of meals to limit its impact on iron absorption. Consuming vitamin C-rich foods can increase iron absorption from plant foods.
- Preparation: Use water that is just shy of boiling (around 190 degrees Fahrenheit or 90 degrees Celsius) to preserve the tea's flavor and nutrients. Steep the tea leaves for approximately 3 minutes to maximize antioxidant activity.
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