I'm gonna have a presentation about extreme obesity (over wight) and need in making an introduction for the presentation.

More information about your presentation would be helpful, but based on what youve given Id say start of with something like,

Im about to present about a very sensetive, very real and present health issue affecting many people around the world. Obesity. Almost 30% of people in the world is obese. In my presentation I will be talking about the causes and effects of obesity and what it truly means to be overweight.

(This is a vague beginning since I dont have much to work on, add detail based of what you are explaining in your presentation about obesity)

Obesity is very common. You have to stay healthy, and well rounded to avoid obesity and anything related. Addicting foods, like chicken and candies, can cause this. Obesity can cause a negative income on health, so make sure to stay healthy!

The littoral zone. . .