绿茶有望对抗肥胖和糖尿病

一种植物提取物改变了豚鼠的肌肉代谢，改善了与葡萄糖相关的过程。绿茶有……

　　

一种植物提取物改变了豚鼠的肌肉代谢，改善了与葡萄糖相关的过程。

绿茶长期以来因其药用和抗氧化特性而备受推崇。其在代谢健康方面的作用，尤其是在肥胖和2型糖尿病等疾病中的作用，已得到广泛研究。最近由FAPESP资助的研究（编号19/10616-5、21 / 08498-4和23/11295-3）为绿茶的作用机制提供了新的见解，并表明使用绿茶治疗可降低肥胖小鼠的体重，并显著改善其血糖敏感性和胰岛素抵抗。这些发现凸显了绿茶作为人类肥胖管理辅助策略的潜在应用。

这项研究由巴西圣保罗南克鲁塞罗大学健康科学跨学科研究生项目的Rosemari Otton领导。Otton研究绿茶已逾15年，她解释说，她最初的兴趣源于质疑绿茶减肥功效的普遍看法是否具有科学依据。她最近的研究成果发表在《细胞生物化学与功能》杂志上。

西式饮食实验

为了探究绿茶对肥胖的影响，研究团队让小鼠接受为期四周的高热量饮食。这种饮食既包含过量脂肪，也包含他们所谓的“自助餐饮食”，旨在模仿典型的西方饮食习惯。“我们给它们喂巧克力、夹心饼干、焦糖牛奶酱、炼乳……换句话说，就是许多人每天都吃的食物，”奥顿说。

在此阶段之后，动物进入12周的治疗期。它们继续进行高热量饮食，但其中一些还被给予标准化绿茶提取物，剂量为每公斤体重500毫克。提取物通过胃管饲法给药，以确保剂量精确。

“这种方法可以确保所有动物都摄入我们想要研究的精确剂量。例如，如果我们把它放在水里，我们就无法知道动物实际摄入了多少，”研究人员说道。对于人类来说，这个剂量相当于每天饮用约3克绿茶，也就是三杯。

标准化提取物的重要性

然而，研究人员表示，并非所有市售绿茶都符合必要的质量标准。“现成的茶包并不能保证其成分的数量或质量。理想的饮用方式是使用标准化的绿茶提取物，例如在复合药房购买的提取物。这是一种浓缩的绿茶利用方式，可以保证其中含有类黄酮，而类黄酮正是绿茶植物中有益健康的化合物，”奥顿指出。

这项研究的一个显著特点是严格控制室温。在整个实验过程中，动物都被安置在温度适中的环境中（28°C）。相比之下，标准动物设施通常将温度保持在约22°C，这对于小鼠来说就是一种慢性寒冷状态。

“过度寒冷会激活动物体内的补偿调节机制，导致它们消耗更多能量来保持温暖。这可能会掩盖任何物质的真实效果，”研究人员解释说。“如果动物处于较冷的环境中，茶的效果会因寒冷引起的能量消耗而增强。但通过保持热中性，我们能够以一种‘干净’的方式观察绿茶的效果，不受环境干扰，”她解释道。

2022年8月发表在《欧洲营养学杂志》上的一项先前研究发现，用绿茶治疗的肥胖小鼠体重减轻了高达30%。“如果一个人的体重减轻5%到10%，那已经是很大的数字了。因此，这项在动物身上取得的成果意义重大，”这位教授说道。

基因表达和代谢改善

这项最新研究的另一个亮点是肌肉形态的保存。肥胖通常会导致肌纤维直径减小，但绿茶可以防止这种肌肉萎缩。“评估肌肉功能的一种方法是观察纤维直径。如果纤维直径增加，就意味着肌肉成分更活跃。绿茶成功地维持了纤维直径，表明它可以保护肌肉免受肥胖的有害影响，”奥顿解释道。

除了形态学数据外，研究人员还评估了与葡萄糖代谢相关的基因表达。绿茶治疗增加了Insr、Irs1、Glut4、Hk1和Pi3k的表达，这些基因对肌肉中葡萄糖的吸收和利用至关重要。乳酸脱氢酶（LDH）的活性也得到了恢复，LDH是葡萄糖代谢所必需的酶。

According to Otton, there is evidence indicating that green tea does not affect the weight of lean animals, suggesting that it acts selectively against excess body fat. “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.”

Another aspect investigated by the team was the action of the compounds in isolation. “Green tea is a complex matrix with dozens of bioactive compounds. 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,” she says.

According to the scientist, one hypothesis explaining the mechanism by which green tea affects obesity involves adiponectin, a protein produced by adipocytes that has anti-inflammatory and metabolic regulation functions. “We conducted a study with adiponectin-knockout mice, meaning they don’t produce it. And in these animals, green tea had no effect. This suggests that adiponectin is a key player in the mechanism of action of the tea,” she comments.

Looking toward human applications

Despite the encouraging results of the mouse study, Otton points out that it is not yet possible to determine a safe and effective dose of green tea for humans. This is mainly due to the variability of the extracts and the fact that each person behaves differently. “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,” she ponders.

The researcher argues that natural and accessible treatments should gain ground in the fight against obesity, especially as alternatives to expensive medications that often have side effects. “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 researcher emphasizes that science always seeks to develop practical solutions. “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.”