My DD did this and won 2nd place, but may only work if you know someone that owns a diabetes kit:
My grandma has to check her blood sugar levels several times a day, so we came up with this idea:
Pick a few different age groups and measure how their blood sugar levels rise after eating a chocolate candy bar.
1st, take each person's blood sugar and record it.
2nd, have each person eat a candy bar.
3rd, retake blood sugar and record the new number
4th, take each person's photo
On the project poster board, she had a chart with all the before & after measurements, each person's picture and age, and some different things posted on the board, such as bandaids lancets (clean and unused, of course), and candy bar wrappers.
Of course you'll have to find participants willing to get their finger pricked!!!
May not be an ideal for everyone, but it was a great subject for DD since she had access to all the diabetes info!