- Guest: Associate Professor Jane Yardley (University of Montreal & Montreal Clinical Research Institute)
- Host: John Pemberton
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Why this episode exists
Exercise guidelines for type 1 diabetes have been built predominantly on research conducted with male participants — yet females face distinct physiological challenges that standard recommendations don’t address. Hormonal fluctuations across the menstrual cycle alter insulin requirements and fuel utilization. Lower muscle mass changes carbohydrate needs during activity. High peripheral insulin levels create unique barriers to fat loss.
Professor Jane Yardley, a leading exercise physiologist in type 1 diabetes, bridges the research gap between male and female exercise physiology. This conversation breaks down how menstrual cycle phases affect glucose management, why fasted exercise offers unique advantages for females with type 1 diabetes, how muscle and bone health in your 20s and 30s determines functional mobility in your 60s and beyond, and why carbohydrate recommendations may systematically overestimate female athletes’ needs. This is the sex-specific exercise guidance that should exist in every clinic.
The female exercise physiology framework
- Menstrual cycle phases: Follicular phase (days 1-14, bleeding starts, relatively stable glucose), periovulatory phase (days 13-15, ovulation, individual variability), luteal phase (days 16-28, progesterone rises, insulin resistance increases).
- Luteal phase insulin resistance: Affects approximately 60-70% of females with type 1 diabetes, typically lasting 3-4 days with insulin needs increasing by 10-50% (average ~10%, but highly individual).
- Fuel utilization differences: Females tend to use proportionally more fat as fuel during exercise compared to males, regardless of exercise type — estrogen promotes fat oxidation.
- Body composition impact: Lower lean muscle mass in females means per-kilogram carbohydrate recommendations (e.g., 0.5-1.0 g/kg) likely overestimate needs — a kilogram of female body mass contains less metabolically active tissue than a kilogram of male body mass.
- Peripheral hyperinsulinemia barrier: Type 1 diabetes creates 4-8× higher peripheral insulin levels than normal physiology — this activates lipoprotein lipase (fat storage) and suppresses hormone-sensitive lipase (fat release), making fat loss extremely difficult through calorie restriction alone.
- Fasted exercise advantage: Exercising before breakfast minimizes insulin on board, promotes fat oxidation via elevated cortisol and growth hormone, reduces hypoglycemia risk, and often requires no insulin adjustments.
- Muscle and bone health window: Peak muscle mass and bone density occur in the 20s-30s —resistance training and weight-bearing activity during this period promote higher functional capacity and lower fracture risk in later decade.
Key takeaways
1) The luteal phase creates predictable insulin resistance
Approximately 60-70% of females with type 1 diabetes experience increased insulin resistance in the late luteal phase (roughly days 22-28 of the menstrual cycle), driven by rising progesterone levels. This typically lasts 3-4 days and can increase total daily insulin requirements by 10-50%, with significant individual variability. Observational data from automated insulin delivery systems shows an average 10% increase, but this masks the reality that some women need 20-30% more insulin while others experience minimal change. AID systems were not designed to account for menstrual cycles and often struggle to keep pace with this rapid shift — average glucose rises from ~130 mg/dL in the follicular phase to ~140 mg/dL in the luteal phase despite the algorithm delivering more insulin.
2) Exercising in the luteal phase may require larger insulin adjustments
Physical activity increases insulin sensitivity, but during the luteal phase, basal rates are already elevated to compensate for progesterone-driven insulin resistance. This means you may have more insulin on board when starting postprandial exercise (exercise after eating) in the luteal phase compared to the follicular phase. Unpublished data from Dr. Yardley’s lab suggests that slightly larger insulin reductions may be needed for luteal phase exercise to avoid hypoglycemia. This is an evolving area of research, but the principle is clear: the same exercise at the same time of day may require different insulin management strategies depending on menstrual cycle phase.
3) Females use more fat as fuel during exercise
Research in people without diabetes consistently shows that females oxidize proportionally more fat during exercise compared to males, regardless of exercise intensity or type. This is thought to be mediated by estrogen, which promotes fat as a fuel source. While we lack robust type 1 diabetes-specific data, this physiological difference likely persists and has implications for carbohydrate supplementation during exercise. If females are relying more on fat oxidation and less on glucose oxidation, standard carbohydrate recommendations (which are largely derived from male-dominant studies) may overestimate needs.
4) Per-kilogram carbohydrate recommendations likely overestimate female needs
Standard exercise carbohydrate guidance (e.g., 0.5-1.0 grams per kilogram of body weight per hour of moderate-intensity exercise) doesn’t account for sex-based differences in body composition. On average, females have higher body fat percentage (18-30% is healthy for females versus 10-16% for males) and lower lean muscle mass. Since muscles are the primary consumers of glucose during exercise, a 70kg female has less metabolically active tissue than a 70kg male — meaning the same per-kilogram prescription will overestimate her carbohydrate needs. Dr. Yardley’s clinical observation: many female participants in acute exercise studies decline the full protocol-mandated carbohydrate supplementation (e.g., refusing all 16 grams of Dextrose tabs when glucose drops to 4.7-4.8 mmol/L), suggesting the amounts don’t match their physiological requirements.
5) Peripheral hyperinsulinemia creates a fat loss barrier
Type 1 diabetes creates a unique metabolic challenge for fat loss. Insulin delivered subcutaneously (via injections or pumps) bypasses the liver and enters peripheral circulation, resulting in 4-8× higher insulin levels in muscle and fat tissue compared to physiological portal vein delivery. High peripheral insulin activates lipoprotein lipase (the “door into” fat cells, promoting fat storage) while suppressing hormone-sensitive lipase (the “door out of” fat cells, preventing fat release). This creates a paradox: reducing calorie intake to create a deficit doesn’t effectively mobilize fat stores because circulating insulin keeps the exit door shut. The result is “starvation from the outside” (reduced food intake) and “starvation from the inside” (inability to access stored fat), making calorie restriction alone an unsustainable strategy for fat loss in type 1 diabetes.
6) Fasted exercise solves the fat mobilization problem
Exercising first thing in the morning before breakfast — with no bolus insulin on board for 8+ hours — creates the metabolic conditions necessary for fat oxidation. Morning fasted exercise offers multiple advantages: no insulin on board from meal boluses (which can have tails lasting up to 6 hours), elevated cortisol and growth hormone levels that promote fat as a fuel source and reduce glucose utilization, minimal hypoglycemia risk (glucose often rises or stays stable during fasted exercise), and no need for insulin adjustments in many cases. This isn’t just theoretical — bodybuilders and fitness competitors have used fasted morning cardio for decades as a cutting strategy to maximize fat burning while preserving muscle. For people with type 1 diabetes struggling with weight management due to high insulin doses (e.g., >1 unit/kg/day), fasted exercise provides a practical, low-risk window to improve insulin sensitivity and access fat stores.
7) Bolus insulin lasts up to 6 hours, not 2-4
The standard teaching that rapid-acting insulin peaks at 2 hours and is “done” by 3-4 hours significantly underestimates the actual duration of action. In reality, bolus insulin has a tail that extends up to 6 hours, particularly for larger doses. If you’re eating multiple meals throughout the day with overlapping boluses, you’re never truly in a low insulin state — which is why exercising 4 hours after lunch, while technically “between meals,” still carries substantial insulin on board and hypoglycemia risk. This also explains why afternoon or evening exercise requires more aggressive insulin reductions and carbohydrate supplementation compared to morning fasted exercise, where you’ve genuinely had 8+ hours without bolus insulin.
8) Fasted exercise simplifies planning and reduces hypoglycemia fear
One of the biggest barriers to exercise in type 1 diabetes is fear of hypoglycemia, and a close second is the planning burden — needing to reduce basal rates or adjust targets 90 minutes before afternoon exercise. Fasted morning exercise eliminates both problems. Dr. Yardley’s research shows that many participants can “roll out of bed and go” without any insulin adjustments and remain euglycemic throughout the session. No pre-planning required. No mid-exercise carbohydrate supplementation. No post-exercise hypos from overcompensating with insulin reductions. This makes exercise more accessible, more consistent, and less mentally taxing — which increases adherence over time.
9) Fasted exercise depletes glycogen and improves all-day insulin sensitivity
Beyond the immediate benefits during exercise, fasted morning activity depletes muscle and liver glycogen stores, creating a metabolic “sink” that improves insulin sensitivity for the rest of the day. When glycogen stores are partially depleted, the body becomes more efficient at taking up glucose from meals to replenish those stores, meaning you may need less insulin for lunch and dinner. This effect is particularly valuable for people with high total daily doses (>1 unit/kg) — fasted exercise becomes a tool to reduce overall insulin requirements, which in turn lowers peripheral insulin levels and makes fat mobilization easier over time.
10) Resistance training in your 20s-30s determines health in your 60s-80s
Peak muscle mass and peak bone density occur in the 20s and 30s. Once you reach that peak, the goal shifts to maintaining it for as long as possible through continued resistance and weight-bearing exercise. If you don’t build a high peak in early adulthood, you have less reserve to draw from as age-related muscle and bone loss accelerates — particularly in females after menopause. The rate of decline in muscle strength, bone density, and functional mobility is much faster in females with type 1 diabetes compared to males with type 1 diabetes or the general population. This translates to higher risk of falls, fractures, loss of independence, and inability to perform activities of daily living (e.g., putting a jar on a high shelf, getting out of a chair unassisted). The intervention window is now — not when you retire.
11) Menopause brings insulin need changes and accelerated health risks
Perimenopause creates chaotic glucose management as estrogen and progesterone levels fluctuate unpredictably rather than following regular cycles. Post-menopause, insulin needs generally decrease — likely due to loss of lean muscle mass, increase in fat mass, and slowing metabolic rate. European database evidence suggests basal insulin needs drop while bolus insulin remains relatively stable, though this is cross-sectional data and causation isn’t proven. More concerning: cardiovascular risk increases sharply in females with type 1 diabetes after menopause (more so than in males with type 1 diabetes), and loss of muscle mass, muscle strength, and bone density accelerates. These risks underscore the importance of building and maintaining physical fitness throughout the lifespan, not waiting until retirement to “start exercising.”
12) Pregnancy exercise data are sparse but principles are clear
Pregnancy with type 1 diabetes carries higher risks: pre-eclampsia, macrosomia (large babies), premature delivery, and even stillbirth. In the general population, physical activity during pregnancy reduces all of these complications — but we lack robust data on safe, effective exercise protocols for type 1 diabetes pregnancy. One controlled study showed that 160 minutes of walking in a 24-hour period significantly improved time in pregnancy range, but this isn’t realistic for most people. The evidence-free but physiologically sound recommendation: reduce sedentary time, walk regularly (especially post-meal to blunt glucose spikes and reduce insulin needs), and maintain as much activity as safely possible. Physical activity helps preserve insulin sensitivity during the second and third trimesters when insulin resistance climbs dramatically, and it may improve lactation outcomes postpartum. Without specific insulin adjustment data, the focus should be on movement rather than structured exercise — walk, don’t sit, and use activity to stay in range (3.5-7.8 mmol/L) rather than relying solely on insulin corrections.
Practical checklist: exercise strategies for females with T1D
General principles across the menstrual cycle:
- Track your menstrual cycle and note patterns in glucose management, insulin needs, and exercise responses
- Expect individual variability — not all females experience luteal phase insulin resistance, and those who do vary in severity (10-50% increase in insulin needs)
- Test the same exercise in different cycle phases (follicular vs luteal) to identify your personal patterns
- Be your own scientist — there is no other body like yours, and research data are too sparse to provide individualized prescriptions
Exercising during the luteal phase (days 16-28):
- Expect higher insulin on board from elevated basal rates compensating for progesterone-driven insulin resistance
- Consider larger insulin reductions for postprandial exercise (e.g., 60-70% basal reduction instead of 50%, or larger meal bolus cuts)
- If using AID systems that struggled to keep up with luteal phase highs, manually increase insulin delivery (e.g., lower glucose targets, shorten active insulin time on compatible systems, use temp basals on others)
- Pre-bolus meals 15-20 minutes before eating to combat insulin resistance
- Walk 10-15 minutes after meals to enhance insulin action without requiring extra carbohydrate
Fasted morning exercise (for fat loss, insulin sensitivity, and hypoglycemia avoidance):
- Wake up, have black coffee (no cream, no sugar — still counts as fasting), and exercise before breakfast
- Start with no insulin adjustments — many people can exercise fasted without changing basal rates or targets
- If glucose rises during fasted exercise (especially high-intensity or resistance exercise), give a small correction bolus after finishing rather than during
- Expect minimal hypoglycemia risk — cortisol and growth hormone promote glucose release from liver and discourage glucose uptake by muscles
- Use fasted exercise as a tool to reduce total daily insulin dose over time, which improves insulin sensitivity and makes fat loss easier
- Suitable for moderate-intensity aerobic exercise (walking, jogging, cycling) and resistance training
Carbohydrate intake during exercise:
- Standard recommendations (0.5-1.0g/kg/hour) likely overestimate female needs due to lower muscle mass and higher fat oxidation
- Start with less than recommended and adjust based on actual glucose response
- If using AID systems, rely on algorithm adjustments first before supplementing with carbohydrate
- For fasted morning exercise, you may need little to no carbohydrate supplementation
Building muscle and bone health (ages 12-30 critical window):
- Incorporate resistance training 2-3× per week minimum (weightlifting, bodyweight exercises, resistance bands)
- Include weight-bearing activities: walking, jogging, dancing, jumping, skipping
- Goal: reach the highest possible peak muscle mass and bone density by age 30
- After age 30, shift focus to maintaining that peak for as long as possible
- Don’t wait until retirement to “start exercising” — by then, much of the protective capacity is already lost
Perimenopause and menopause considerations:
- Expect chaotic glucose patterns during perimenopause as hormones fluctuate unpredictably
- Post-menopause, monitor for decreasing insulin needs (particularly basal insulin)
- Prioritize resistance training to slow age-related muscle and bone loss
- Maintain activity levels to reduce sharply increased cardiovascular risk
Pregnancy exercise (evidence-sparse, apply general principles):
- Reduce sedentary time — movement of any kind improves blood flow and glucose management
- Walk after meals (15-20 minutes) to keep glucose <7.8 mmol/L (140 mg/dL) without extra insulin
- Focus on physical activity (general movement) rather than structured exercise unless you have specific insulin adjustment protocols
- Activity helps preserve insulin sensitivity during second/third trimester insulin resistance
- Consult your diabetes and obstetric teams before starting or changing exercise routines
Guest
Associate Professor Jane Yardley is a leading exercise physiologist specializing in type 1 diabetes at the University of Montreal’s School of Kinesiology and Physical Activity Sciences and the Montreal Clinical Research Institute (IRCM). Her research spans resistance exercise, high-intensity interval training, fasted versus fed exercise, menstrual cycle impacts on glucose control, and pregnancy. Dr. Yardley’s work challenges standard exercise guidelines by revealing that factors like insulin on board, time of day, and sex-based physiology often matter more than exercise type alone. She is a key contributor to international type 1 diabetes exercise guidelines (ISPAD, ADA) and co-authored a landmark review on women’s health in type 1 diabetes. Dr. Yardley’s approach combines rigorous exercise physiology with a pragmatic focus on reducing barriers to physical activity — particularly fear of hypoglycemia and the planning burden that prevents people from moving consistently.
Connect with Dr. Yardley:
- Type 1 Better Registry: type1better.com (Canadian participants can join, all can access expert resources)
Disclaimer
The content available in The Glucose Never Lies® guides is for informational purposes only. Reading or listening to the content does not constitute medical advice and is not a substitute for individualized care, and does not create a clinician–patient or therapeutic relationship with The Glucose Never Lies® or any guest. Always discuss any changes to your diabetes management with your healthcare team. Exercise responses vary significantly based on menstrual cycle phase, insulin on board, fitness level, and individual physiology — work with your diabetes team to develop safe, personalized strategies.
Episodes on women’s health and diabetes
- 31 — Pregnancy with Type 1 Diabetes (Prof. Eleanor Scott)
- 32 — Menstrual Cycles & Type 1 Diabetes (Dr. Cecilia Nobili)
