Why Women Gain Weight on the Same Diet as Men: Fueling, Fasting, and Biology with Dr. Stacy Sims

In this episode of unPAUSED, Dr. Mary Claire Haver sits down with exercise physiologist and nutrition scientist Dr. Stacy Sims to unpack why so much fitness and diet advice built on male physiology leaves women confused about why the scale will not move, and why weight loss can feel so much harder for women than for men on the exact same plan. Dr. Sims, author of Roar and Next Level, a former professional cyclist who has taught and coached at Stanford, breaks down why women following the same diet and training program as their male partners often end up tired and stuck rather than leaner and fitter.

The conversation covers the biological reasons women conserve fat in a calorie deficit, how female circadian rhythm differs from male circadian rhythm, and why eating within an hour of waking helps regulate cortisol and appetite hormones like ghrelin and peptide YY. Dr. Sims explains why fasted workouts can backfire for women, why front loading calories earlier in the day supports better metabolic outcomes, and why time restricted eating works with a woman's biology in ways that intermittent fasting often does not.

Dr. Haver and Dr. Sims also dig into strength training for women in perimenopause and menopause, including why lifting heavier weights helps preserve fast twitch muscle fibers, power, and proprioception, all of which decline earlier in women than in men. They discuss the connection between high intensity exercise and lactate production, and why lactate is a preferred fuel for brain metabolism that may help protect against cognitive decline and dementia risk. The episode also touches on bone density and osteoporosis risk after menopause, the difference between calories in versus food quality and timing, and practical guidance on microdosing melatonin for better sleep.

Throughout the conversation, Dr. Sims makes the case that women's health depends on training and eating in ways that reflect female biology at every life stage, and that building muscle and bone during midlife matters more than chasing thinness.

Guest links:

• Dr. Stacy Sims
  
• Dr. Stacy Sims (Facebook)
  
• Dr. Stacy Sims (YouTube)
  
• Dr. Stacy Sims (Instagram)
  
• Stacy T. Sims, PhD (LinkedIn)
  
• Dr. Stacy Sims Newsletter
  
• Dr. Stacy Sims Microlearning Course

Books:

• “Menopause and Beyond,” by Dr. Stacy Sims
  
• “ROAR: How to Match Your Food and Fitness to Your Unique Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life,” by Dr. Stacy Sims
  
• “The New Perimenopause,” by Dr. Mary Claire Haver
  
• “The New Menopause,"⁠ by Dr. Mary Claire Haver

Articles:

• Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity (JAMA Internal Medicine)
  
• Randomized controlled trial for time-restricted eating in healthy volunteers without obesity (Nature Communications)
  
• Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans (Nutrients)
  
• Changes in Physical Activity and Body Composition in Postmenopausal Women over Time (Medicine & Science in Sports & Exercise)
  
• The Impact of Walking on BDNF as a Biomarker of Neuroplasticity: A Systematic Review (Brain Sciences)
  
• Lactate and BDNF: Key Mediators of Exercise-Induced Neuroplasticity? (Journal of Clinical Medicine)
  
• Physiological and molecular sex differences in human skeletal muscle in response to exercise training (The Journal of Physiology)
  
• Women Have Higher Protein Content of β-Oxidation Enzymes in Skeletal Muscle than Men (PLoS One)
  
• Effectiveness of nature-based walking interventions in improving mental health in adults: a systematic review (Current Psychology)
  
• The 2022 hormone therapy position statement of The North American Menopause Society (Menopause)
  
• Epigenetics of prenatal stress in humans: the current research landscape (Clinical Epigenetics)
  
• Placental H3K27me3 establishes female resilience to prenatal insults (Nature Communications)
  
• Stress during pregnancy: Fetal males pay the price (PNAS)
  
• Minimizing Injury and Maximizing Return to Play: Lessons from Engineered Ligaments (Sports Medicine)
  
• Creatine in women's health: bridging the gap from menstruation through pregnancy to menopause (The Journal of the International Society of Sports Nutrition)
  
• Does Creatine Supplementation Enhance Performance in Active Females? A Systematic Review (Nutrients)
  
• Single-Dose Creatine Reduces Sleep Deprivation-Induced Deterioration in Cognitive Performance (Nutrients)
  
• Single dose creatine improves cognitive performance and induces changes in cerebral high energy phosphates during sleep deprivation (Nature)
  
• Biological sex differences in fatigue in resistance-trained individuals: A scoping review (International Journal of Sports Medicine)
  
• The effects of biological sex on fatigue during and recovery from resistance exercise (PeerJ)
  
• Sex Differences Are Here to Stay: Relevance to Prenatal Care (Journal of Clinical Medicine)
  
• Male excess among anatomically normal fetuses in spontaneous abortions (American Journal of Medical Genetics)
  
• Effect of Fetal Sex on Maternal and Obstetric Outcomes (Frontiers in Pediatrics)
  
• Sex Differences in Vulnerability to Prenatal Stress: a Review of the Recent Literature (Current Psychiatry Reports)
  
• Early sex-dependent differences in response to environmental stress Get access Arrow (Reproduction)
  
• Elevated risk of stillbirth in males: systematic review and meta-analysis of more than 30 million births (BMC Medicine)