You probably heard about insulin before. It’s the hormone that’s released when you eat those tasty carbohydrates and that makes you fat. At least, that is
Let’s go back to the bodybuilders who inject insulin. They inject insulin at incredibly high doses that cannot be produced in our body naturally, and yes that approach seems to be effective to increase muscle protein synthesis. Warning: it’s extremely dangerous and NOT recommended.
So what about regular fitness people who use dietary approches to manipulate circulating insulin levels?
In the fitness world it’s common advice to eat carbohydrates after resistance training to stimulate insulin production which is supposed to stimulate muscle growth.
However, the majority of the scientific literature suggests that it won’t help.
It’s much more important to get your protein after resistance training.
A protein shake or meal provides you with the amino acids needed to stimulate muscle protein synthesis. And as my review pointed out, there’s not a single study that shows that insulin has any benefit for muscle protein synthesis when you have enough amino acids in your blood, which is the case if you drank your protein shake.
In line with these insulin injection studies, the addition of carbohydrates to protein also has no effect of muscle protein synthesis (1).