When people think about fertility, insulin is rarely the first hormone that comes to mind. Yet insulin plays a quiet but powerful role in shaping the metabolic conditions in which reproductive hormones operate.
As a key metabolic signal, insulin communicates whether the body perceives safety, energy availability, and stability. When insulin signalling is steady, hormones such as oestrogen, progesterone, testosterone and thyroid hormone are more likely to rise and fall in a coordinated, predictable way. When insulin is dysregulated, that coordination can begin to falter long before anything appears abnormal on a standard blood test.
This is why supporting healthy blood sugar regulation is one of the most important — and often overlooked — foundations of fertility. It doesn’t create fertility on its own, but it removes metabolic noise that can quietly interfere with ovulation, implantation, egg and sperm development, and early pregnancy.
What exactly is insulin?
Insulin is a hormone produced in the pancreas. Its primary role is to regulate how the body metabolises carbohydrates, fats and protein by promoting the uptake of glucose into liver and fat cells.
Insulin’s release is controlled by a sensitive feedback loop involving the beta cells of the pancreas.
Beyond its metabolic role, insulin also sits upstream of major reproductive hormones. It influences the production of:
• DHEA → which converts to testosterone and oestrogen
• Pregnenolone → which converts to progesterone
When insulin becomes dysregulated, these downstream hormones can shift out of balance.
What causes dysglycaemia?
Here we are not talking about diabetes, but the far more common everyday imbalance called dysglycaemia — when blood sugars fluctuate outside the ideal range because of diet, sleep, stress or lifestyle patterns.
Blood glucose naturally moves within an upper and lower limit. When levels move outside that range, the body must compensate. Over time, this constant correction can impact fertility.
Common drivers of dysglycaemia include:
Carb / fat / protein balance in meals
Fibre intake
Skipping meals
Eating late at night
Shift work
Pregnancy
Chronic stress
Poor sleep
Caffeine
Artificial sweeteners
Chewing gum
Dehydration
Intensity and timing of exercise
Even small misalignments across the day can create hormonal ripple effects.
5 ways insulin affects fertility
The hormone hierarchy shows how insulin sits above the steroid hormones involved in conception. When insulin is out of balance, these effects can be subclinical — not always visible on blood tests — yet still powerful enough to disrupt baby-making physiology.
Here are five of the most meaningful downstream effects.
Increased adiposity (especially visceral fat)
Excess glucose is first stored in the liver for quick energy use. Once that storage is full, insulin converts additional glucose to fat — particularly visceral fat around the abdomen and internal organs.
This is one reason belly fat can be so resistant to calorie restriction; lowering calories can further dysregulate insulin and make the situation worse.
You do not need to meet the criteria for obesity to have visceral fat. Because body fat can increase oestrogen production, excess visceral fat may contribute to higher oestrogen levels.
Oestrogen dominance
In men, oestrogen should be in balance with testosterone. Too much oestrogen relative to testosterone can reduce sex drive and impair sperm production.
In women, oestrogen dominance can lead to:
• Irregular menstrual cycles
• Failure to ovulate
• Short luteal phases
• Increased risk of early miscarriage
When insulin is dysregulated, it can easily shift this oestrogen–progesterone balance.
Insulin resistance
When blood sugars remain elevated and the liver can no longer store excess glucose, the body may develop insulin resistance. Cells stop responding to insulin’s signal, leaving glucose trapped in the bloodstream.
This leads to:
• Increased insulin production
• Energy crashes
• Intense sugar or carb cravings
• Chronic low-grade inflammation
Inflammation and high circulating insulin can disrupt hormone balance, egg development, ovulation, and sperm integrity — including DNA fragmentation.
Egg and sperm quality
DHEA — a hormone heavily influenced by insulin — plays a vital role in egg growth and quality during the months before ovulation. Lower DHEA levels are often seen in women with diminished ovarian reserve.
Dysglycaemia can also interfere with:
• Testosterone production in men (necessary for sperm generation)
• Progesterone levels in women (low levels can cause anovulation or luteal phase defects)
• Sperm motility and morphology
Even mild insulin dysregulation can quietly weaken egg and sperm potential.
Thyroid function and early pregnancy
Thyroid hormone affects every cell in the body. It regulates energy, temperature, metabolism, menstrual cycles, digestion, mood and fertility.
During early pregnancy, the embryo relies on maternal thyroid hormone for rapid cell division.
Dysglycaemia can disrupt thyroid function, leading to:
• Irregular or heavy cycles
• Anovulatory cycles
• Miscarriage risk
• Fatigue and low mood
Because thyroid function is foundational to conception and early pregnancy, insulin balance becomes essential.
Optimising your fertility by supporting insulin balance
It is rare for me to see a new fertility client without some degree of dysglycaemia — and that gives us a powerful place to begin.
Even when there is a known fertility condition such as low AMH, the fundamentals of blood sugar balance remain relevant. When insulin is steady, the entire reproductive system stabilises.
Inside a Fertility Consultation, we look at your unique patterns — your daily rhythms, stress load, sleep, meal timing, cravings, energy dips, and how these influence your hormonal environment. This is where we begin to piece together what your body is trying to tell you and what needs to shift to support egg and sperm development.
Because nothing in the body works in isolation, we also look gently at the wider landscape: stress physiology, thyroid health, shift-work patterns, and the practical steps that help you feel in control of your fertility again.
When your intention is to optimise your fertility — naturally or ahead of IVF — one of the most impactful places to start is with your plate. And if you’d like personalised guidance, a Fertility Consultation is the clearest next step.
