You may be able to find many useful videos about dietetics and nutriton using YouTube. Try searching with a keyword such as "dietetics" or "nutrition" with a phrase such as "why study nutrition" or "case study." Searching with the phrase "American Dietetic Association" may yield interesting results.
NOTE: YouTube is a classic example of one of the strengths and weaknesses of the Internet, which is the fact that anyone can post videos. As such, the quality and scholarly acceptability of videos varies greatly. There may be useful video clips on YouTube, but you must EVALUATE them for authority and relevance. Before referencing any material from YouTube (or other video sites on the Internet) in a paper or using a clip in a presentation, though, it is highly advisable to check with your instructor concerning the acceptability of the video for the assignment.