When is the right time to eat a food source that is packed with protein? Is it before your exercise session or after? Our bodies use several energy sources during an exercise bout that allows for our bodies to sustain high muscular power outputs. These come in the form of our macronutrients: carbohydrates (sometimes referred to as glucose and/or glycogen), fats, and proteins. However, while protein is one of the main components of our diet, the amount of energy it provides is approximately only ten percent of the total energy needed to sustain the exercise bout (Luc, Van Loon, 2014). In other words, protein should not (and can not) be your primary source of fuel during exercise (carbohydrates are! Read that blog post here).
You may have heard or seen individuals consuming protein shakes or bars prior to exercise. While exercise can increase skeletal muscle protein synthesis (the rebuilding of skeletal muscle fibers, resulting in strength or endurance improvements), protein consumption before exercise has been shown to provide little energy throughout the exercise session. Consequently, a majority of the protein ingested pre-exercise goes towards protein synthesis post exercise and not towards energy intake (Luc, Van Loon, 2014). Thus, while that protein shake or bar can help post-workout (see below), it is not the primary or optimal fuel pre-workout.
The two main anabolic stimuli needed for protein synthesis (muscle rebuilding) are physical activity and protein ingestion post exercise. Studies suggest that a post-exercise meal containing protein can increase the rate of protein synthesis (muscle rebuilding) for an additional 2-5 hours post exercise (Luc, Van Loon, 2014). After a bout of exercise, the body is already in a heightened state of muscle protein synthesis from exercise stimuli and adding protein ingestion post exercise can maximize the muscle protein synthetic response leading to gaining more muscle (Luc, Van Loon, 2014).
Thus, post exercise consumption of protein has been shown to have more benefits to the body than pre-exercise. While protein consumed within the context of a carbohydrate based meal can be an appropriate pre-workout snack (see separate blog post), focus on consuming adequate protein throughout the day and especially post-workout. Most people do well with between 20-35g of protein after exercise, but work with your Registered Dietitian to customize a plan best for you. Meat, fish, poultry, eggs, soy products, low fat dairy products, nuts/nut butters, seeds, and legumes can all provide great sources of protein at your first meal post-workout rounded out by appropriate portions of complex carbohydrates and produce.
Luc,, J.,& Van Loon, C., (2014). Is there a need for protein ingestion during exercise?
Sports Medicine, 44, 105-111.