https://phys.org/news/2018-08-cell.html

"We can use this technology to visualize metabolic activities in a wide range of animals," said the study's senior author Wei Min, a chemistry professor at Columbia University. "By tracking where and when new proteins, lipids and DNA molecules are made, we can learn more about how animals develop and age, and what goes wrong in the case of injury and disease."

The breakthrough involves the use of heavy water as a chemical tracer. Made by swapping water's hydrogen atoms with their heavier relative, deuterium, heavy water looks and tastes like regular water and in small doses (no more than five tablespoons for humans) is safe to drink. Once metabolized by cells in the body, heavy water is incorporated into newly made proteins, lipids and DNA, where the deuterium forms chemical bonds with carbon.