Green Tea Shows Significant Benefits for Glucose Metabolism and Muscle Health in Mice with Obesity

Key Takeaways: 

• Green tea extract significantly improved insulin sensitivity, glucose tolerance, and muscle preservation in mice with obesity, even when they continued consuming a high-calorie diet.
• The study controlled for temperature effects, providing clearer evidence that green tea’s metabolic benefits are independent of cold-induced energy expenditure.
• Findings suggest a potential role for green tea as a safe, accessible adjunct to obesity treatment in humans, though exact dosing for people remains to be established.
  

Ancient beverage, modern research

Green tea, long valued for its medicinal and antioxidant properties, continues to attract scientific interest for its impact on metabolic diseases such as obesity and type 2 diabetes. A recent study led by Professor Rosemari Otton from the Interdisciplinary Graduate Programme in Health Sciences at Cruzeiro do Sul University in São Paulo, Brazil, offers new insights into how green tea affects metabolism.

Otton, who has dedicated over 15 years to the study of green tea, explained that her initial curiosity stemmed from the popular belief that green tea promotes weight loss. The findings of her latest research, published in Cell Biochemistry & Function, reinforce the potential of green tea as a therapeutic adjunct in managing obesity.

Study design and green tea administration

The research team first fed mice a high-calorie diet for four weeks, including both a fat-rich diet and a “cafeteria diet” to replicate a Western-style eating pattern. “We give them chocolate, filled cookies, dulce de leche, condensed milk… In other words, the same type of food that many people consume on a daily basis,” said Otton.

After this induction phase, the mice continued on the high-calorie diet for 12 weeks, with some receiving a standardised green tea extract at 500mg per kilogram of body weight via intragastric gavage. This method ensured precise dosing. “If we put it in water, for example, we’d have no way of knowing how much the animal actually ingested,” Otton explained.

For humans, this dose would equate to approximately 3 grams of green tea daily — roughly three cups. However, Otton cautioned that not all commercial products meet required standards:

“Ready-made tea bags do not always guarantee the quantity or quality of the compounds. The ideal for consumption would be to use standardised green tea extract, like those found in compounding pharmacies. This is a concentrated way of using the plant, with a guarantee of the presence of flavonoids, which are the health-beneficial compounds present in the green tea plant.”

Controlled conditions for reliable results

A distinctive feature of the study was the use of a thermoneutral environment at 28°C, eliminating confounding effects caused by chronic cold exposure. Mice are typically kept at around 22°C in animal facilities, a temperature that triggers energy expenditure to maintain body heat.

“Excessive cold activates compensatory regulatory mechanisms in the animals’ bodies, causing them to expend more energy to stay warm. This can mask the real effects of any substance,” Otton explained. “By maintaining thermoneutrality, we were able to see the effects of green tea in a ‘clean’ way, without environmental interference.”

A previous study published in European Journal of Nutrition (August 2022) found that obese mice treated with green tea lost up to 30% of their body weight — a reduction Otton described as highly significant:

“If a person loses 5% to 10% of their body weight, that’s already a lot. So this result in animals is very significant.”

Preservation of muscle health

One of the most striking findings of the latest study was the preservation of muscle fibre morphology. Obesity often leads to a reduction in muscle fibre diameter, but green tea helped maintain muscle structure.

“One way to assess muscle function is to look at fibre diameter. If it increases, we have more active muscle components. Green tea managed to maintain this diameter, showing that it protects muscle against the harmful effects of obesity,” Otton said.

Genetic and metabolic insights

The study also explored gene expression related to glucose metabolism. Green tea treatment enhanced the expression of genes such as Insr, Irs1, Glut4, Hk1, and Pi3k, all of which play a role in glucose uptake and utilisation in muscle tissue. Additionally, the activity of lactate dehydrogenase (LDH), an enzyme vital for glucose metabolism, was restored.

Otton noted that green tea appeared to have a selective effect:

“It makes obese animals lose weight but keeps lean animals at a balanced weight. This shows that the tea seems to need an environment with excess nutrients to act, which supports the hypothesis that it acts directly on fat cells.”

Synergy of bioactive compounds

Green tea contains dozens of bioactive compounds, and attempts to isolate them have proven less effective than using the whole extract.

“We’ve tried to separate these compounds and study their effects individually, but the whole extract is always more effective. There’s a synergy between the compounds that we can’t reproduce when they’re isolated,” Otton explained.

One mechanism under investigation involves adiponectin, a protein secreted by fat cells that regulates inflammation and metabolism. In mice genetically modified to lack adiponectin, green tea showed no effect — pointing to adiponectin as a key mediator of its benefits.

Translating findings to human health

Despite these promising findings, Otton cautioned that safe and effective doses for humans have yet to be established, owing to variability in extracts and individual responses. She stressed the importance of long-term, habitual consumption rather than expecting rapid results:

“The ideal is chronic consumption, as we see in Asian countries. In Japan, for example, people consume green tea every day, throughout their lives, and obesity rates are low. But this is different from drinking tea for five months and expecting a miraculous weight loss effect.”

Otton also emphasised the importance of accessible and safe treatment options:

“The idea is to have safe, natural, effective, and high-quality compounds. The Camellia sinensis plant offers this. We’re still studying all the compounds involved, but there’s no doubt that green tea, as a plant matrix rich in flavonoids, has important therapeutic potential.”

The road ahead

Finally, Otton underscored the need for caution when translating animal research to clinical practice:

“What we see in animals doesn’t always reproduce in humans. But if we want to make this translation to real life, we need to think about all the details, such as ambient temperature. It’s these precautions that increase the validity of our data. We’re far from having all the answers, but we’re getting closer and closer.”