Fasted vs Fueled Workouts: What Women Need to Know for Hormones, Muscle, and Recovery

This protocol is the cornerstone of Sims' recommendation for women who train early. She acknowledges the reality of the 5 a.m. club: getting up at 4:30 to eat a meal isn't feasible. So she designs the refuel around convenience. The key is to get some amino acids and glucose into the bloodstream. She suggests making a cold brew with protein powder and milk or almond milk the night before, so it's ready to drink on the go. Alternatively, a small smoothie with protein powder and fruit works. If you're at home and have a few minutes, a quarter cup of low-fat Greek yogurt with a drizzle of honey provides both protein and fast-digesting carbs. After training, you can have a full breakfast. This small habit change can dramatically alter hormonal outcomes and training results. Sims stresses that even if you train later (like 9 a.m.), you should split your breakfast: eat half 1.5 hours before, then the other half after. The overall goal is to never train completely fasted, thus maintaining an anabolic environment and stable hormone pulses.

Sims lays out a multi-layered argument. First, she stresses that women's circadian clocks are timed earlier, so a fasted workout and coffee early in the morning effectively delays the melatonin peak, which then disrupts the pulsatile secretion of reproductive hormones throughout the day. Many women think of cycle hormones as a smooth daily level, but they actually pulse every 90 minutes, and altering the circadian rhythm can change those concentration profiles. This becomes an additional physiological stressor that raises inflammation. She then connects inflammation to infertility, referencing a conversation with Dr. Natalie Crawford about how inflammation is a major driver of infertility. While a 20‑something might not be focused on fertility, the inflammatory state from fasted exercise and circadian disruption can still affect hypothalamic sensitivity to nutrient density. The hypothalamus, receiving signals of stress without incoming fuel, triggers a conservation response: downregulation of metabolism, breakdown of lean mass, and increased stress hormone production. The result is a catabolic state that not only raises inflammation and cortisol but also interferes with the body's ability to build muscle and bone. Sims argues that simply consuming a small amount of protein and carbohydrate before exercise (e.g., protein coffee) prevents this entire cascade by signaling that fuel is available, stopping the hypothalamic alarm and preserving normal hormone pulses and muscle protein balance.

Sims explains that the normal morning cortisol peak is already high; adding caffeine and exercise on an empty stomach pushes it even higher. This spike is accompanied by a rise in acylated ghrelin, the active hunger hormone. In the absence of food, the hypothalamus receives conflicting signals: the body is in a high-alert state but has no incoming nutrients. It interprets this as an emergency, triggering neuropeptide Y and other pathways that promote energy conservation and muscle protein breakdown. The result is a catabolic state that specifically targets lean mass, undermining any training aimed at building strength or muscle. This mechanism is distinct from the slower metabolic adaptation to chronic fasting; it's an acute stress response that happens every time a woman trains fasted with caffeine. Even a small amount of protein and carbohydrate, she says, would dampen this response by providing substrate, preventing the brain from perceiving starvation and stopping the breakdown signals.

Sims presents the solution as deceptively simple: by providing the body with a small influx of amino acids and glucose, the fasted stress cascade is avoided. The pre-workout snack prevents the phase shift in melatonin and the blunting of hormone pulses. It also blunts the cortisol and ghrelin response, so the hypothalamus no longer gets the 'empty tank' alarm. This, in turn, stops the catabolic signaling and preserves lean mass. She emphasizes that the amount of food is minimal—no need for a full meal—and that options like a protein coffee or a small smoothie can be prepared the night before, making it practical even for the 5 a.m. club. The downstream benefits go beyond the workout: better sleep quality, improved metabolic control, and enhanced ability to change body composition. This small behavior change has a ripple effect throughout the entire endocrine and recovery system.