New research suggests that the human body undergoes two significant phases of physical transformation and molecular change during middle age. Scientists at Stanford University tracked age-related changes in more than 135,000 molecule types and microbes. The study sampled over 100 adults and found that significant molecular shifts typically occur at around two specific ages. "Obviously you change throughout your entire life. But there are two major periods when there are many changes: One is when people hit their mid-40s, and one is they hit their 60s," said Michael Snyder, a geneticist at Stanford University. For those in their mid-40s, the molecular changes were linked to the metabolism of alcohol and lipids. For those in their 60s, the changes are related to immune regulation, kidney function, and the metabolism of carbohydrates.