You Are What You Just Ate
If you really want to understand how protein contributes to new muscle, you need to be able to follow the individual components—amino acids—on their journey inside your body.
Starting in 2009, van Loon and his colleagues developed a technique that involved infusing 40,000 euros’ worth of amino acids, specially “labeled” using a rare and trackable isotope, into a cow. Then they milked the cow and, 24 hours later, slaughtered it. The result: milk and beef that can be tracked with painstaking precision as it progresses from a person’s mouth to their biceps by taking frequent samples of blood and biopsied muscle tissue in the hours after a meal.
In
one of the resulting studies, the researchers found that substantial amounts of the “glowing cow” protein was incorporated into muscles within just two hours of ingesting it. As the study’s title proclaims, you are, quite literally, what you just ate. Just over 50 percent of the protein made it into the subjects’ circulation within five hours, with the rest presumably taken up by tissues in the gut or not absorbed. During the same period, 11 percent of the ingested protein was incorporated into new muscle.
Overall, van Loon points out, we break down and rebuild 1 to 2 percent of our muscle each day, meaning that you completely rebuild yourself every two to three months. This is a message, van Loon hopes, that might persuade people to think a little more carefully about what they put in their mouths.
