Leyla Weighs In: Carbs, Protein, and Metabolism–What the Research Really Says

Carbs vs Protein During Exercise: Hormones, Cortisol, and Insulin. Registered dietitian nutritionist Leyla Muedin discusses an emailed study request about a 2013 Iranian paper comparing carbohydrate vs protein drinks consumed during resistance exercise in 20 fasted young men. The study found cortisol rose much more in the protein group while insulin rose more in the carbohydrate group, with no significant differences in growth hormone, testosterone, or IGF-1, and it concluded carbohydrates created a “better hormonal environment.” Leyla challenges this interpretation, arguing cortisol’s rise is a normal and useful exercise stress response for muscle breakdown and subsequent repair, while carbohydrate-driven insulin spikes can blunt cortisol and promote fat storage; she also notes methodological limits (drinking during exercise, unclear drink ingredients, low protein dose, and unmeasured amino acids/protein turnover). She recommends exercising fasted, avoiding sweet/starchy intake during and immediately after exercise, hydrating, then eating a protein-focused meal 45–60 minutes post-workout.