What Happens If I Eat a Protein Shake Before a Workout?

With so much conflicting advice, figuring out the proper nutrition for exercise is hard: Do you drink a protein shake before or after a workout? Do you even need one? There's no "right" or "wrong" way, but research shows that drinking a shake afterward may be better than a dose of pre-workout protein.

But it's not just about when you're having your protein shake. According to research, the amount of protein you eat could matter more than the timing. In other words, as long as you're getting enough protein, it doesn't matter when you consume it.

Your body is very good at adjusting its physiology to meet your current needs and to prioritize whatever it's doing. Because of this, when you're exercising, your body focuses on supplying blood and oxygen to the organs and muscles that really need it at the time — decreasing blood flow to any areas that don't.

Your digestive system has its own blood supply, called the splanchnic circulatory system, that directs blood flow to all of the organs of the digestive tract, including the stomach, intestines, pancreas and liver.

When you exercise, your body recognizes that these digestive organs aren't the current priority. It naturally decreases the amount of blood sent to the splanchnic circulatory system and increases the amount of blood in the tissues that you're using the most: your heart, muscles and brain.

When it does this, your digestion shuts down temporarily. However, if you have a pre-workout protein shake, the food in your digestive tract signals the body to increase blood flow to the splanchnic circulatory system, and your digestive system and exercising muscles wind up competing for blood.

Because your digestive system and your muscles and heart are competing for blood, they both don't get enough and, as a result, they're both affected negatively. Your body becomes less effective at digesting the protein, and you may experience uncomfortable gastrointestinal symptoms, like gas, bloating, abdominal cramps or nausea.

While this is happening, your heart and muscles also aren't getting all the blood they need to power through your workout at full capacity. Because your body is trying to prioritize both digestion and exercise at the same time, you may experience fatigue sooner and it might be harder to get through an entire workout.

This effect is magnified when you eat protein or fat before a workout, because the two macronutrients move through the digestive system more slowly than carbohydrates, which your body can use up fairly quickly.

There is, however, some research that says drinking a pre-workout protein shake before a workout may increase the number of calories you burn.

A study published in the Journal of the International Society of Sports Nutrition in November 2018 reported that people who consumed protein before a 30-minute moderate-intensity treadmill workout burned more calories and more fat during the workout than people who didn't eat anything or consumed carbohydrates instead.

The study went on to say that the type of protein matters, too. Researchers compared whey protein isolate to casein protein isolate and discovered that the casein protein increased calorie-burn and fat-burn more significantly.

Another study published in Sports Medicine in May 2014 found that consuming protein before a workout helps increase muscle synthesis, or the creation of new muscle, and helps the skeletal muscle adapt to extended periods of exercise. In other words, protein helps build new muscle and prevents the muscles you're using from getting fatigued.

Read more: 7 Popular Protein Myths Totally Busted by Science

However, that same study also notes that when you consume the protein after working out instead of before, the rate of muscle synthesis is actually higher and lasts up to 24 hours following the exercise.

Research reported in a December 2012 issue of the American Journal of Clinical Nutrition also agreed with these results, stating that consuming protein after resistance training can increase the rate of muscle synthesis in both young and old adults.

Another study published in the_ International Journal of Sport Nutrition and Exercise Metabolism_ in December 2012 tested the effect of consuming whey protein before and after exercise and reported that neither timing had a positive effect on muscle mass or strength.

Because of the mixed results regarding whether it's better to have a protein shake before or after a workout, a study published in the_ Journal of the International Society of Sports Nutrition_ in December 2013 concluded that timing may not be as important as simply making sure you're getting enough protein throughout the day to support muscle synthesis.

Read more: 11 Easy Post-Workout Foods and the Science of Why They Work

Because having a protein shake right before a workout can lead to uncomfortable digestive symptoms, and because the research is mixed about whether there's a real benefit to it, it makes sense to focus on making sure you're getting enough protein throughout the day, rather than whether you eat protein before or after a workout.

The general protein recommendation is 0.8 grams per kilogram of body weight, but because your protein needs are increased when you're exercising, the International Society of Sports Nutrition recommends boosting your intake to 1.4 grams to 2.0 grams per kilogram of body weight if you're exercising regularly and want to increase your lean muscle mass.

This means that, if you weigh 150 pounds, you should aim for between 95 and 136 grams of protein per day, spread out between meals.

If you do eat a protein shake before your workout, time it so that you're consuming it between one and three hours before you start exercising. That way, you can reap the benefits of the protein without experiencing any of the negative digestive symptoms.

If you're short on time and need to eat within 10 to 15 minutes of working out, opt for a carbohydrate-rich source of fuel, like an apple or a banana.