Episode 33 — Exercise, Hormones, and Type 1 Diabetes in Females

In this episode

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 do not address. Hormonal fluctuations across the menstrual cycle alter insulin requirements and fuel utilisation. Lower lean muscle mass changes carbohydrate needs during activity. High peripheral insulin levels create unique barriers to fat loss.

Professor Jane Yardley bridges the research gap between male and female exercise physiology. This conversation explores how menstrual cycle phases affect glucose management, why fasted exercise offers particular advantages for females with type 1 diabetes, how muscle and bone health in your twenties and thirties shapes functional mobility decades later, and why carbohydrate recommendations may systematically overestimate female athletes’ needs.

The female exercise physiology framework

• Menstrual cycle phases: Follicular phase (days 1–14, relatively stable glucose), periovulatory phase (days 13–15, individual variability), luteal phase (days 16–28, progesterone rises, insulin resistance tends to increase).
• Luteal phase insulin resistance: Affects approximately 60–70% of females with type 1 diabetes, typically lasting three to four days, with insulin needs increasing by 10–50% on average — but this varies significantly between individuals.
• Fuel utilisation differences: Females tend to use proportionally more fat as fuel during exercise compared to males, regardless of exercise type — oestrogen appears to promote 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.
• Peripheral hyperinsulinaemia barrier: Type 1 diabetes creates four to eight times higher peripheral insulin levels than normal physiology — this activates fat storage enzymes and suppresses fat release, making fat loss very difficult through calorie restriction alone.
• Fasted exercise advantage: Exercising before breakfast minimises insulin on board, promotes fat oxidation, reduces hypoglycaemia risk, and often requires no insulin adjustments.
• Muscle and bone health window: Peak muscle mass and bone density occur in the twenties and thirties — resistance training and weight-bearing activity during this period are associated with higher functional capacity and lower fracture risk later.

Key themes

1. The luteal phase tends to create 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), driven by rising progesterone. This typically lasts three to four days and can increase total daily insulin requirements by 10–50%, with significant individual variability. AID systems were not designed to account for menstrual cycles and often struggle to keep pace with this shift.

2. Exercising in the luteal phase may require different insulin strategies

Physical activity increases insulin sensitivity, but during the luteal phase, basal rates are often already elevated to compensate for progesterone-driven insulin resistance. The same exercise at the same time of day may require different insulin management strategies depending on menstrual cycle phase — this is worth exploring with your care team and your own CGM data.

3. Females tend to use more fat as fuel during exercise

Research in people without diabetes consistently shows that females oxidise proportionally more fat during exercise compared to males, regardless of exercise intensity or type. This appears to be mediated by oestrogen. If females are relying more on fat oxidation and less on glucose oxidation, standard carbohydrate recommendations — largely derived from male-dominant studies — may overestimate needs.

4. Per-kilogram carbohydrate recommendations likely overestimate female needs

Standard exercise carbohydrate guidance does not account for sex-based differences in body composition. On average, females have higher body fat percentage and lower lean muscle mass. Since muscles are the primary consumers of glucose during exercise, a 70 kg female has less metabolically active tissue than a 70 kg male — meaning the same per-kilogram prescription may overestimate her carbohydrate needs.

5. Peripheral hyperinsulinaemia creates a fat loss barrier in type 1 diabetes

Insulin delivered subcutaneously bypasses the liver and enters peripheral circulation, resulting in four to eight times higher insulin levels in muscle and fat tissue compared to physiological delivery. High peripheral insulin activates fat storage while suppressing fat release — this makes calorie restriction alone an unsustainable strategy for fat loss in type 1 diabetes.

6. Fasted morning exercise creates conditions for fat oxidation

Exercising before breakfast — with no bolus insulin on board for eight or more hours — creates the metabolic conditions for fat oxidation. Morning fasted exercise is associated with no insulin on board from meal boluses, elevated cortisol and growth hormone that promote fat as a fuel source, minimal hypoglycaemia risk, and no need for insulin adjustments in many cases.

7. Bolus insulin lasts longer than standard teaching suggests

The standard teaching that rapid-acting insulin peaks at two hours and is done by three to four hours significantly underestimates the actual duration of action. In practice, bolus insulin has a tail that extends up to six hours, particularly for larger doses — which has implications for exercise timing and hypoglycaemia risk throughout the day.

8. Fasted exercise depletes glycogen and tends to improve all-day insulin sensitivity

Beyond the immediate effects during exercise, fasted morning activity depletes muscle and liver glycogen stores, creating a metabolic state that may improve insulin sensitivity for the rest of the day. This effect tends to be particularly relevant for people with high total daily doses.

9. Building muscle and bone in your twenties and thirties shapes health decades later

Peak muscle mass and peak bone density occur in the twenties and thirties. The rate of decline in muscle strength, bone density, and functional mobility tends to be faster in females with type 1 diabetes compared to males with type 1 diabetes or the general population. The intervention window is early adulthood — not retirement.

10. Menopause brings insulin need changes and accelerated health risks

Perimenopause creates unpredictable glucose patterns as oestrogen and progesterone fluctuate. Post-menopause, insulin needs generally decrease. Cardiovascular risk increases sharply in females with type 1 diabetes after menopause, and loss of muscle mass and bone density accelerates — underlining the importance of maintaining physical fitness throughout the lifespan.

11. Pregnancy exercise data are limited but general principles are clear

Pregnancy with type 1 diabetes carries higher risks. In the general population, physical activity during pregnancy reduces complications — but robust data on safe, effective exercise protocols for type 1 diabetes pregnancy are limited. Reducing sedentary time, walking regularly (especially after meals), and maintaining as much activity as safely possible are the physiologically sound starting points. Always discuss exercise plans during pregnancy with your diabetes and obstetric teams.

Practical exploration checklist

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
• Test the same exercise in different cycle phases to identify your personal patterns
• Your CGM data is the most useful tool for exploring where you sit on the distribution

Fasted morning exercise — possible advantages to explore

• Exercise before breakfast, before the first bolus of the day
• Start with no insulin adjustments — many people find they can exercise fasted without changing basal rates or targets
• Suitable for moderate-intensity aerobic exercise and resistance training
• Discuss with your care team before making changes to your management routine

Carbohydrate intake during exercise — a starting point for exploration

• Standard recommendations may overestimate female needs due to lower lean muscle mass and higher fat oxidation
• Start with less than recommended and adjust based on actual glucose response
• For fasted morning exercise, you may need little or no carbohydrate supplementation

Building muscle and bone health

• Incorporate resistance training two to three times per week (weightlifting, bodyweight exercises, resistance bands)
• Include weight-bearing activities: walking, jogging, dancing, jumping
• After age thirty, shift focus to maintaining the peak you have built

About the guest

Associate Professor Jane Yardley is a leading exercise physiologist specialising 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, and pregnancy. Dr Yardley 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.

Connect with Dr Yardley:

• LinkedIn profile
• Type 1 Better Registry (type1better.com)

Related episodes

• Episode 31 — Pregnancy with Type 1 Diabetes (Prof. Eleanor Scott)
• Episode 32 — Menstrual Cycles and Type 1 Diabetes (Dr Cecilia Nobili)
• Episode 7 — Fundamentals of The GNL
• Episode 8 — Activity snacking and time in range
• Episode 18 — Exercise without fear (Othmar Moser)
• Episode 29 — Five Principles of T1D Behaviour Change