在撰写关于肥胖的英语作文时，开头部分应该引人入胜，并明确阐述文章的主题。以下是一些建议：
引入话题：
可以通过描述当前社会现象或健康问题来引入肥胖这一话题。例如：“Nowadays, the people are enjoying a more comfortable life, yet many are suffering from obesity, which has become a pressing health concern.”
提出问题：
通过提出一个引人关注的问题来引起读者的兴趣。例如：“Obesity is a subject of concern that is getting as big as people's waste-lines. It affects many people on a daily basis and also affects the way they interact with others. Why is this a growing problem？”
强调重要性：
可以直接强调肥胖对健康的危害，从而引起读者的重视。例如：“Obesity is a major threat to health and longevity. It is associated with a range of diseases, including heart disease, diabetes, and some forms of cancer.”
提供背景信息：
可以通过一些统计数据或研究结果来提供背景信息，帮助读者更好地理解问题的严重性。例如：“According to the World Health Organization, obesity rates have tripled since the 1970s, affecting both developed and developing countries.”
选择哪种方式开头取决于你想要传达的信息和文章的整体结构。确保开头部分简洁明了，能够迅速吸引读者的注意力，并为后续的论述打下良好的基础。