Fasted training burns more fat… but doesn’t reduce more body fat | Dr. Stacy Sims explains

The host directly asks whether women should ingest protein before training, given the fasted training debate. Dr. Sims agrees, citing the higher calorie threshold and kisspeptin sensitivity. While the host personally enjoys fasted training, he acknowledges that the physiology for women demands a different approach. The suggestion to use a protein shake is practical for those who don't want solid food in their stomach pre-workout.

The host states this is his personal belief and that he's delighted by the recent cultural shift toward both men and women resistance training. He recalls taking his sister to the gym when it was empty of women and the fear of 'looking like a bodybuilder.' Dr. Sims shares similar memories and celebrates the current popularity. While the specific number 2–3 per week isn't backed by cited studies in this segment, it is presented as a pragmatic, attainable goal that balances efficacy with recovery.

Mentioned in the same sentence as resistance training by the host, who frames them as a pair of ideals. No further elaboration is given in this segment, but it reflects a common public health guideline for cardiorespiratory fitness.

The host opens by noting that the discussion around fasted training burning more body fat has largely been settled: while the proportion of fat used as fuel increases during a fasted session, the overall loss of body fat over time is the same whether you train fed or fasted. Dr. Stacy Sims confirms this unequivocally, adding that this doesn't mean one cannot train fasted if they prefer, but for women the implications are different due to higher energy requirements for endocrine function. The conversation turns to practical advice: the host, who himself likes fasted training, asks whether women should ingest protein beforehand. Sims agrees, explaining that women have a lower tolerance for low energy availability because kisspeptin—a key hormone regulator—requires adequate carbohydrate and calorie intake. Thus, for women, going into a training session without fuel can increase the risk of hormonal disruption, even if total fat loss is the same as training fed.

Dr. Stacy Sims introduces the concept of a 'tipping point' for endocrine dysfunction: for men it occurs at 15 calories per kilogram of fat-free mass, while for women it is 30. This means women need roughly double the baseline calorie intake relative to lean mass to keep hormones like kisspeptin functioning optimally. Kisspeptin is a neuropeptide that up-regulates gonadotropin-releasing hormone, affecting menstrual cycles and overall endocrine health. Sims explains that women's higher carbohydrate requirements are rooted in this kisspeptin-driven system, which is far more sensitive to energy deficits than in men. She traces this back evolutionarily, suggesting it was not advantageous to become pregnant under low-calorie conditions, but emphasizes it is relevant today because women's hormonal regulation across the circadian rhythm demands more energy. This explains why men often tolerate fasted training or one-meal-a-day patterns while women may experience perturbed cycles.

Dr. Sims recounts how she was often the only woman on a lifting platform in her youth, whereas now platforms are crowded with women. When women start lifting, the rapid increase in strength surprises many because they assume muscle mass growth is required. Sims explains that strength comes from the nervous system: motor neurons release acetylcholine, stimulating muscle fibers more effectively and recruiting a greater number of fibers. This 'neural' adaptation happens quickly and yields significant strength gains without visible hypertrophy. She emphasizes that it takes a long time for women to add bulk, as the main driver is neurological. The host adds a unique insight about the 'pump': during resistance training, increased blood flow gives a transient, visual preview of what potential hypertrophy could look like—a somatic snapshot that is unique to this type of exercise. This window can reassure women that the muscle size they see during a workout is temporary and not a permanent change.