Let’s clear up one misperception here:
Recent research has confirmed that different tissues in the body replace cells at different rates, and some tissues never replace cells. So the statement that we replace every cell in the body every seven years or every ten years is wrong. Using a revolutionary new technique (described below), researchers have shown that:
Neurons in the cerebral cortex are never replaced. There are no neurons added to your cerebral cortex after birth. Any cerebral cortex neurons that die are not replaced.
Fat cells are replaced at the rate of about 10% per year in adults. So you could say that on average, human beings replace all their fat cells about every ten years.
Cardiomyocyte heart cells are replaced at a reducing rate as we age. At age 25, about 1% of cells are replaced every year. Replacement slows gradually to about 0.5% at age 70. Even in people who have lived a very long life, less than half of the cardiomyocyte cells have been replaced. Those that aren’t replaced have been there since birth.
In essence, that replacement “fact” is also an illusion.