Charting weight loss over time

Hey!
I am trying to create a weight loss worksheet to show weight loss a couple of years ago for a presentation and I would like to keep it set up the way I have it but need help with some of the functions. I have a large table with each day of the experiment comprising a row. On the day I entered the "Weight", The calorie intake, and exercise performed. I have several entries and am trying to create a table that summarizes the results by weeks. I would like that table to be a weekly tally and have the information written from the Saturday of each week. I have been trying to do it with "Index" and "Match" and weekday but haven't been able to.

Can someone please help?! Thanks!

I attached a copyWeight Loss.xlsx

That gave me huge numbers. I'm looking more for a lookup. That will take the current weight on each saturday and put it in the other table and so on with the other data. So I can condense it from a huge table with a lot of days to a simpler weekly format.

Thank you! That worked perfectly. I'm also trying to figure out the average intake calories (InCal) per day for the week and also the total exercise calories (ExCalories) . . . ?

I just put ExCalories where week is and it gave me nearly 8000 for the 0 week and 0 for the rest . . . am i doing something wrong?