I ate a peanut butter sandwich in 1973 when I was 10 years old. Is it likely that any of those molecules are still in my body? I was still growing then, so have some of those molecules permanently become part of my bones, etc? Theoretically, do I have molecules in my body from every meal I have ever eaten?
Theoretically I would say yes, or at least possible.
The answer is complex as some things in your body are very short lived and some very long lived. So, I would think some nutrients from a given meal may be perpetually stored in some long lived cells.
Try this for a more complete answer: http://www.madsci.org/posts/archives/2000-09/968860088.Bc.r.html
Peanuts contain calcium
Most calcium in your body is in your bones
At age 10 your bones were in the process of adding mass (adding calcium)
Bones do not undergo as rapid of cell replacement as the rest of your body - so you probably still have at least one atom of calcium from that sandwich in your bones.
Just as a guess but calcium would seem most likely to last this long.
I know I’m still carrying molecules from many previous meals.