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肥胖元凶:糖分or脂肪?

加里·陶布斯

    ①为什么我们身边有那么多人变得肥胖?这个问题似乎不难回答。世卫组织认为,肥胖及超重的根本原因是,能量摄入和消耗的不平衡。简单地讲,就是这些人吃得太多,运动太少,或者两者兼而有之。按照这个解释,人体任何多余的热量,不管于蛋白质、碳水化合物还是脂肪,最终都会转化为体重。因此,肥胖的解决方法说到底还是——少吃,多运动。

    ②另一种激素假说则将焦点集中在脂肪细胞的生理调节机制上。他们认为,体重上升的根源在于,日常食物中的碳水化合物让体内胰岛素水平居高不下。富含碳水化合物和糖分的谷类食物的摄入使得血糖(葡萄糖)浓度上升,激活机体分泌更多的胰岛素,以维持血糖的稳定,造成胰岛素抵抗。胰岛素还会发出信号,使脂肪细胞停止向机体供能,并可能促进脂肪的积聚。过去20年中,越来越多的证据表明,这一假说的观点或许是正确的。过多的碳水化合物和糖分的摄入,不仅是肥胖和2型糖尿病,甚至也是心脏病乃至癌症的重要诱发因素。所以,通过严格的实验,弄清楚碳水化合物和胰岛素的影响,就显得尤为重要。

    ③由于此类实验的最终目的在于准确找出诱发肥胖的环境因素,因此,最理想的情况应该是直接通过实验去寻找导致多余脂肪积聚的生理机制。但是,肥胖的产生过程往往需要数十年,人体在几个月中积累的脂肪量往往很少,很难检测得到。所以NuSI机构的研究人员逆向思考,打算第一步先通过减肥实验来检验不同假说,这样得出结论所需的时间就可以短很多。

    ④在整个实验期间,16名超重和肥胖的受试者将会受到“严格监控”,各种实验设备会精确检测他们摄入的热量,以及消耗的能量。在实验的第一阶段,受试者得到的食物类似当今美国人的日常饮食——由50%的碳水化合物、35%的脂肪以及15%的蛋白质构成。而在第二阶段,食物所含热量不会改变,但食物结构则会完全不同。调整后,饮食中碳水化合物所占的比重非常低——仅有5%,而且是肉类、鱼类、家禽类、蛋类、奶酪、动植物油以及绿色蔬菜中天然携带的碳水化合物。蛋白质的比重仍占热量摄入的15%。至于剩下80%的热量,则都由以上日常食物中所含的脂肪来补充。需要注意的是,这个实验的目的并不是测试上述饮食方式是否健康,是否可在日常生活中长期维持,而是希望通过这样的手段,在最短的时间内,最大限度地降低受试者体内的胰岛素水平。

    ⑤这个实验创造了非常理想的环境,可以很好地检验出哪一个肥胖假说是正确的。如果能量失衡假说成立,这些受试者在实验结束时体重将不会变化,因为他们摄入和消耗的热量始终会相互抵消。如此的话,目前比较流行的看法将从理论上被证明,肥胖确实和摄入的热量直接相关,不管热量是来自脂肪、碳水化合物还是蛋白质,效果是一样的。如果食物结构会影响脂肪积聚,那在碳水化合物摄入量受限的情况下,受试者体重和脂肪量都会下降,这将是对激素假说的强力支持,说明在胰岛素的作用下,与脂肪或蛋白质相比,碳水化合物更易使人发胖。

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    Health experts are calling for action to increase cancer care and control in the developing world. A medical research paper says cancer was once thought of as a problem mostly in the developed world. But now cancer is a leading cause of death and disability in poor countries as well. Experts from Harvard University and other organizations urge the international community to fight cancer actively, saying it should be fought in the way HIV/AIDS has been fought in Africa.

    Cancer kills more than 7.5 million people a year worldwide. Almost two thirds are in low-income and middle-income countries.

    They discover cancer kills more people in developing countries than AIDS, tuberculosis and malaria combined. But the world spends only 5﹪ of its cancer resources in those countries.

    Felicia Knaul from Harvard Medical School was one of the writers of the paper. She was in Mexico when she was found to have breast cancer. She received treatment there and her experience showed her the sharp difference between the rich and the poor in treating breast cancer.

    Felicia Knaul says, “And we are seeing how this is attacking young women. It's the number two cause of death in Mexico of women thirty to fifty-four. All over the developing world, it's the number one cancer-related death among young women. I think we have to again say that there is much more we could do about it than we are doing about it. ”

    Professor Knaul met community health workers during her work in developing countries. They were an important part of efforts to reduce deaths from the cancer. They were able to persuade people to get tested to prevent the illness. The experts say cancer care does not have to be costly. For example, patients can be treated with lower-cost drugs.