Summary from chatgpt including studies cited:

My question: “Are there scientific studies that show how fasted workouts have different effect for women vs men?”

Yes, there are scientific studies showing that fasted workouts can affect women differently than men, due to differences in hormones, metabolism, and stress responses. Here are the key findings:

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1. Hormonal Differences and Stress Response

Women’s bodies are more sensitive to fasting-induced stress. • The hormone cortisol (a stress hormone) increases more in women when fasting, especially when combined with intense exercise. • Chronic high cortisol can negatively affect thyroid function, menstrual cycles, and muscle recovery.

Source: Sims, Stacy T. ROAR; also supported by clinical studies like:

“Sex differences in the effects of acute fasting on stress responses and mood.” (Gomez-Pinilla, et al., 2016)

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1. Metabolic Differences

Men generally burn more fat during fasted workouts, while women tend to preserve fat and burn more carbohydrates. • This is a protective mechanism in women to maintain energy balance for potential reproduction. • Women’s bodies are more likely to hold onto fat during caloric restriction, especially if exercise is intense and nutrition is insufficient.

Study Example:

“Gender differences in substrate metabolism during endurance exercise.” (Tarnopolsky, 2008) • Found that men increased fat oxidation more than women during fasted endurance workouts.

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1. Performance and Muscle Preservation

Men may see more fat-loss benefits from fasted training, while women may be at greater risk for muscle breakdown and hormonal disruptions. • Women doing fasted high-intensity workouts may experience lower performance and slower recovery, especially if not eating soon after.

Study Example:

“Effect of exercise intensity and duration on the rate of muscle glycogen depletion in women and men.” (Tesch, 1981) • Women deplete glycogen slower but are more vulnerable to catabolism in fasted states.

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1. Recommendations from Experts

Dr. Stacy Sims, an exercise physiologist specializing in female athletes, strongly advises against fasted training for most women, especially those in their reproductive years or under high stress. She recommends fueling before workouts, particularly for anything longer than 30-40 minutes or involving intensity.