One thing that stands out right away is your audio levels are not even. Sometimes they are loud, other times they are soft, and sometimes we have absolutely no sound in the background. We need sound in every shot but we have to be careful of their levels. In Final Cut, look at the audio meters. The line that moves up and down when you play your video needs to fall between -6 and 0 in the meter. They should not be below or higher. You also need to keep background audio in all of your shots. Your shots are pretty good and your voices are nice and clear although the levels need to be adjusted. However in that shot of Lukas on the second day, I can hear some other audio that shouldn't be in there, like someone else talking in the background. Another thing I noticed is that your actors wear the same clothing in all of your shots, even though they are supposed to be drinking sodas and asking about it on two different days. That's a problem. It's hard to sell me the idea that this is happening on two different days when I see the father and son wearing the same clothes on both days. These are details that may seem minor but do make a big difference. Also be careful on your focusing. Your first shot is out of focus.
Your message at the end needs work. "Just one soda per day you can gain 10 pounds in a year," is not a complete sentence. It's not a good sentence at all and needs to be rewritten to something like, "Drinking just one soda per day can cause you to gain 10 pounds in a year." Your title gets cut off on the sides and needs to be adjusted to stay within the frame with a little room. You also need to do a voice over of the lines and add them in. You are also over the limit by 2 seconds. You need to trim this down to 30 seconds exactly. This is pretty good but needs some work. Good to great!
Write something about yourself. No need to be fancy, just an overview.