A human body has about 37 trillion cells [1] (not including our about 39 trillion bacterial cells [2]). About 100 billion of those cells are replaced every day [3], making 36.5 trillion cell replacements a year. Old cells are gifted to the biosphere as poop, dead skin, nail clippings, etc, and new cells are made out of food. But that doesn’t mean that 99% of the body is replaced, because some cells will be replaced many times. The lining of your intestine is replaced every couple days, while red blood cells last a few months, and fat cells last years [4]. But only female egg cells, the core cells of your eye lens, and neurons last your whole life.
If your body is constantly changing, what makes you stay you? Scientists once thought it was your DNA. But your DNA also changes with every cell replacement, because there are 100 - 200 mutations every time DNA is replicated to make a new cell [5]. What about your mind? The contents of your mind - your memories - change too, since memories alter as soon as we revisit them [6]. So what is left that makes baby you and adult you the same individual? It is the arrows connecting the many versions of you, the continuity from beginning to end, the same sort of continuity that makes the beginning and end of a story part of the same story. You are a process.
[1] https://www.nationalgeographic.com/science/article/how-many-cells-are-in-your-body
[2] https://doi.org/10.1101/036103
[3] https://www.ncbi.nlm.nih.gov/books/NBK10103/
[4] http://book.bionumbers.org/how-quickly-do-different-cells-in-the-body-replace-themselves/