The results of this study are interesting—but what’s really amazing is how the study was done.
The basic goal was to compare the impact of two different sources of protein as a post-workout meal: milk and beef. To do that, researchers from Luc van Loon’s group at Maastricht University injected a cow with amino acids specially labelled with a rare isotope of carbon. Then they milked the cow and had it slaughtered to produce meat, and fed the specially labeled milk and meat to their subjects!
Going to all that trouble allowed the researchers to track the progress of the protein through the body through a series of muscle biopsies in the hours after a strength-training workout. The results, which were published a few months ago in the American Journal of Clinical Nutrition (thanks to Trent Stellingwerff for the tip), suggest that there’s not much difference between them.
Here’s the rate of muscle protein synthesis (i.e. how fast the body is building new muscle or repairing old muscle) at various points after working out and then consuming 30 grams of protein from either skim milk (350 mL) or ground beef (158 grams):
Milk versus beef for protein synthesis.
You can see that milk has an edge two hours after workout, possibly because it has a higher level of leucine, an amino acid that helps to trigger muscle synthesis. But the rates are equal after five hours, and if you add up the total postexercise muscle protein synthesis during that period, there’s no significant difference between the groups.
The context here is that lots of previous studies have looked at isolated proteins—things like whey powder or soy protein—rather than the actual foods that people often eat, which also contain carbohydrate and fat that can influence how the protein is digested and processed.
It’s possible that there would have been bigger differences between milk and meat if the protein amounts had been smaller (30 grams is the equivalent of about five large eggs). But as long as you’re getting enough protein, there doesn’t seem to be much to choose between them.
It would be interesting to see this kind of study extended to all the other kinds of proteins people eat, like eggs and chicken and various vegetable proteins. Slightly bigger differences may emerge, but the general message I take from this is that you shouldn’t sweat the details.
I should also mention the usual caveat I add when discussing postworkout fueling. It’s important if you’re trying to get bigger, if you’re training at an extremely strenuous level, or if it’s going to be many hours before your next meal. But most of us, in most contexts, don’t need to worry about it at all. We’re getting all the calories we need throughout the day.