Intra-workout nutrition is the fuel consumed during physical activity to sustain energy and performance. Many people assume a protein shake will feed the muscles while they are working. For most workouts, especially those under 90 minutes, protein is not the primary fuel source the body requires mid-session. Whether you should drink a protein shake while exercising depends entirely on the duration and intensity of your effort.
Is Protein Necessary During Exercise?
The body’s physiological needs during a typical training session do not prioritize whole protein consumption. During exercise, the body primarily relies on stored carbohydrates, known as muscle glycogen, and circulating glucose for energy. Protein’s main function is to serve as a building block for muscle repair and growth, not as a rapid fuel source.
Exercise stimulates both muscle protein synthesis (MPS) and muscle protein breakdown (MPB). However, research indicates that MPS is suppressed during the activity itself. The major anabolic response, where muscle growth is stimulated, occurs most effectively after the workout is complete, during recovery. Pre-workout and post-workout protein intake is usually sufficient to maximize muscle-building signals.
Specialized amino acid supplements, such as Branched-Chain Amino Acids (BCAAs), can be used as a direct energy source during prolonged activity. BCAAs may also help suppress muscle protein breakdown, especially when training in a fasted state. However, consuming a complete protein shake offers no significant performance advantage over optimizing total daily protein intake.
Digestive Practicalities of Intra-Workout Shakes
Consuming a standard protein shake, particularly one based on whey or casein, during moderate to high-intensity exercise presents a significant physiological challenge. When the body works hard, it redirects blood flow away from the internal organs, including the digestive tract, and toward the working skeletal muscles.
This redirection means the gastrointestinal (GI) system is suppressed and cannot function efficiently. Introducing complex macromolecules like protein requires substantial digestive effort, which the compromised gut is ill-equipped to handle. The result is often gastric distress, manifesting as bloating, nausea, cramping, and a feeling of heaviness.
Even in liquid form, the complex structure of protein demands time and enzymatic activity for proper breakdown and absorption. This slow process can cause the shake to sit uncomfortably in the stomach, leading to poor nutrient absorption and negatively impacting training performance.
Prioritizing Carbs and Hydration
The body’s true intra-workout needs focus on maintaining blood glucose levels and managing fluid balance. Carbohydrates are the most efficient fuel for sustained, high-output activity because they are rapidly converted into glucose. When exercise extends beyond 60 to 90 minutes, or is performed at high intensity, the body depletes muscle glycogen stores, leading to fatigue and a drop in performance.
Consuming simple carbohydrates during these longer sessions helps spare muscle glycogen and provides a steady energy supply to the muscles and central nervous system. These carbohydrates are best consumed in a liquid solution, such as specialized sports drinks or diluted powders (like dextrose or maltodextrin). Liquid solutions promote rapid gastric emptying and absorption, allowing the fuel to quickly enter the bloodstream without overloading the stomach.
Hydration is equally important, as fluid loss through sweat quickly impairs performance. Effective intra-workout drinks contain electrolytes, such as sodium and potassium, which are lost in sweat. Electrolytes are necessary for maintaining proper fluid balance, nerve signaling, and muscle contractions. Prioritizing a carbohydrate-electrolyte solution addresses immediate performance needs without burdening the digestive system.