Does cardio effect the amount of protein I absorb after a weight lifting session?

Question

I know there is a window for drinking my protein shake after lifting weights, about 15-30 mins after I finish the session.

But if after my session, I do about 45 minutes of cardio, how will that impact the effect my protein shake has?

Answer 1

As the study that Greg cites shows, there is no real difference in the window for protein intake. People may be confusing this with the studies that show supercompensation of glycogen storage when carbohydrates are consumed in the period ("the golden hour") after prolonged aerobic exercise.

However, you may want to reconsider doing cardio immediately following your weightlifting routine. Studies such as this one suggest that protein catabolism (Breakdown of protein for energy) is higher when exercising in a glycogen depleted state, with associated high nitrogen losses (which would impair muscle rebuilding, which needs a positive nitrogen balance).

That is also reinforced by another study. In this one, they deliberately induced low glycogen in one leg and then exercised both, with the low glycogen leg showing greater protein degradation (This was confirmed with blood sampling and muscle biopsies) than the "normal" leg.

What that all basically means, is that by exercising aerobically after a weightlifting session, you may be creating even more of a protein/nitrogen deficit, since the glycogen in the muscles is depleted, which can hurt the rebuilding of the muscle you have stressed during the weightlifting.

Here is another good read on nutrient timing, with a lot of really good attendant cited studies.

Answer 2

It won't.

As long as you meet your daily requirements you will be fine, regardless how many minutes after your workout you will have a shake.