She had been doing everything right.
Eating well, training consistently, managing her sleep, working on her stress. And yet she was exhausted in a way that sleep didn’t fix. Her weight had been slowly and steadily increasing despite genuine consistency with her food and her training. Her hair was coming out in the shower in quantities that alarmed her. Her hands were perpetually cold. Her brain felt like it was operating through fog until at least 10am.
When we spoke, one of the first things I asked was whether she had explored her thyroid health with a functional medicine practitioner or integrative GP. She hadn’t, and hadn’t thought to. Like many women, she associated the thyroid with dramatic symptoms and assumed her situation wasn’t severe enough to warrant investigation.
What I have noticed consistently in women over 40 is that thyroid function is one of the most commonly overlooked pieces of the body composition and energy puzzle. Not because it isn’t relevant, but because the connection between lifestyle factors, hormonal change, and thyroid health is rarely explained in a way that makes it actionable.
The thyroid is one of the most important and most underappreciated glands in the female body. And after 40, it deserves a great deal more attention than it typically receives.
What the Thyroid Actually Does
The thyroid is a small butterfly-shaped gland sitting at the base of the throat. It produces two primary hormones, thyroxine (T4) and triiodothyronine (T3), that govern the metabolic rate of virtually every cell in the body.
Think of the thyroid as the body’s metabolic thermostat. It determines how quickly cells convert nutrients into energy, how efficiently the body burns fuel at rest, how fast the heart beats, how well the gut moves, how the brain processes information, and how effectively the body maintains its temperature. Its reach is extraordinary, influencing mood, cognition, digestion, body weight, fertility, skin, hair, heart rate, cholesterol levels, and muscle function.
T4 is the storage form of thyroid hormone, produced in large quantities but relatively inactive. For the body to use it, T4 must be converted to T3, the active form, primarily in the liver, kidneys, and gut. This conversion step is where things most often go wrong in women over 40, and where lifestyle factors have the most significant influence.
Why Women Over 40 Are Disproportionately Affected
Thyroid disorders are significantly more common in women than in men, women are five to eight times more likely to develop thyroid conditions across their lifetime. And the perimenopause transition creates a specific set of conditions that make thyroid function particularly vulnerable.
The oestrogen connection
Oestrogen influences thyroid hormone binding proteins, the proteins that carry thyroid hormones through the bloodstream. As oestrogen fluctuates in perimenopause, these binding proteins change, affecting how much thyroid hormone is available to cells. The thyroid may be producing adequate hormone, but the hormone may not be reaching its destination effectively.
Oestrogen and thyroid hormones also share conversion pathways. When oestrogen is fluctuating, as it does so erratically in perimenopause, these pathways can become congested, reducing the efficiency of T4 to T3 conversion.
The cortisol connection
Chronically elevated cortisol, which we explored in Week 21, directly suppresses thyroid function. It reduces TSH production, impairs the conversion of T4 to active T3, and instead promotes the conversion of T4 to reverse T3 (rT3), an inactive form that blocks thyroid receptors without activating them. A woman under chronic stress may have adequate thyroid hormone production but significantly reduced thyroid function at the cellular level.
This is one of the most important connections in the whole hormonal picture: stress doesn’t just affect cortisol. It suppresses the thyroid. And a suppressed thyroid slows the metabolism, worsens fatigue, impairs body composition, and deepens the very exhaustion that stress creates.
The diet connection
Several dietary patterns common among health-conscious women over 40 can inadvertently suppress thyroid function.
Chronic caloric restriction reduces T3 levels, the body responds to energy scarcity by slowing the metabolic rate, and the thyroid is the primary instrument through which it does so. Extended fasting has the same effect. Research published in the journal Thyroid found that caloric restriction significantly reduces active T3, with effects that persist well beyond the restriction period itself.
Very low carbohydrate diets impair the conversion of T4 to T3. The thyroid requires adequate glucose availability for this conversion, and persistent carbohydrate restriction creates a low-glucose environment that slows it. This is why some women on long-term ketogenic or very low-carb diets report worsening fatigue, cold intolerance, and weight stagnation over time, despite initial results.
Nutritional deficiencies also play a significant role. The thyroid requires iodine as a raw material for hormone production. It requires selenium for the conversion of T4 to T3. Zinc, iron, and vitamin D all support thyroid function. Many women over 40, particularly those eating restricted diets, are low in one or more of these nutrients without knowing it.
Signs Your Thyroid May Need Support
The symptoms of suboptimal thyroid function overlap significantly with those of perimenopause, chronic stress, and iron deficiency, which is one reason they are so frequently missed or misattributed. If several of the following are familiar, thyroid function is worth exploring with a thorough panel:
- Persistent fatigue that is not relieved by sleep
- Weight gain or inability to lose weight despite genuine consistency with food and exercise
- Hair thinning or increased shedding
- Cold hands and feet, or general cold intolerance
- Brain fog, slow thinking, or poor memory
- Constipation or slow digestion
- Dry skin, brittle nails
- Low mood or depression that doesn’t have a clear external cause
- Elevated cholesterol (the thyroid governs cholesterol metabolism)
- Puffiness, particularly around the face and eyes
- Slow heart rate or a general sense of physical sluggishness
It is worth noting that hyperthyroidism, an overactive thyroid, produces the opposite picture: unexplained weight loss, racing heart, anxiety, heat intolerance, and insomnia. Both directions of thyroid dysfunction are worth awareness, though hypothyroidism (underactive) is significantly more common in women over 40.
If This Resonates – Where to Go Next
The symptoms of suboptimal thyroid function overlap significantly with those of perimenopause, chronic stress, and iron deficiency, which is one reason they are so frequently missed or misattributed. If several of the signs above feel familiar, it is worth raising thyroid health specifically with a functional medicine practitioner or integrative GP who can explore the full picture alongside you.
What I can tell you with confidence, as a holistic health coach, is that the lifestyle factors within your control – your nutrition, your cortisol load, your sleep, your stress management, and the nutritional sufficiency of your diet, have a direct and meaningful influence on thyroid health. That is the territory we work in together inside the Strong Calm Lean Method. And for many women, addressing these foundations creates a meaningful shift in how they feel.
What Supports Thyroid Function – Within Your Control
- Eat adequate carbohydrates: complex, whole-food carbohydrates support the T4 to T3 conversion that very low-carb diets impair. This does not mean eating refined carbs, it means including sweet potato, oats, legumes, fruit, and wholegrains consistently.
- Do not chronically under-eat: prolonged caloric restriction suppresses T3. Eating particularly enough protein and enough total calories to support your training and your metabolic needs, is one of the most direct ways to support thyroid output.
- Manage cortisol: everything we covered in Weeks 21 and 26 about nervous system regulation, sleep, and stress management applies here directly. Cortisol suppression of the thyroid is one of the most significant and most addressable lifestyle factors in thyroid health.
- Support nutritional sufficiency: iodine (found in seaweed, fish, eggs, and dairy), selenium (Brazil nuts are an exceptionally rich source, just two per day provides a full daily intake), zinc (red meat, pumpkin seeds, legumes), iron (red meat, lentils, leafy greens with vitamin C for absorption), and vitamin D (sun exposure and supplementation where levels are low) all play roles in thyroid function.
- Reduce inflammatory load: chronic inflammation suppresses thyroid conversion. The gut health strategies from Week 22, the anti-inflammatory dietary principles, and the nervous system regulation work all support a less inflammatory internal environment in which the thyroid can function better.
- Be cautious with raw cruciferous vegetables in large quantities: raw broccoli, cauliflower, kale, and cabbage contain compounds called goitrogens that can interfere with thyroid hormone production when consumed in very large amounts in raw form. Cooking deactivates most of these compounds, and moderate consumption of cruciferous vegetables is not a concern for most people, but this is worth knowing if you are already managing thyroid issues and consuming very large quantities of raw greens daily.
The Strong Calm Lean Connection
Every pillar of the Strong Calm Lean Method supports thyroid health.
Strength training supports metabolic rate and improves the hormonal environment in which the thyroid operates. Adequate protein and whole-food carbohydrates provide the nutritional foundations for thyroid hormone production and conversion. Nervous system regulation reduces the cortisol burden that suppresses thyroid function. And addressing the subconscious stress patterns that keep the body in a chronic state of perceived threat, one of the most persistent drivers of cortisol elevation, creates the physiological safety the thyroid needs to do its job well.
The thyroid is not an isolated gland. It is a deeply connected part of an integrated hormonal system. And when the whole system is supported, as the Strong Calm Lean Method is designed to do, the thyroid tends to come along for the ride.
If the symptoms in today’s article sound familiar – the fatigue, the weight that won’t shift, the brain fog, the hair loss – I’d love to hear what’s going on for you.
Book a complimentary Roadmap Call and let’s look at your full picture together. I’ll listen to what’s happening in your unique physiology, and if I feel I can help, I’ll share the options to work with me inside the Strong Calm Lean Method. It’s a no-pressure conversation, and you’ll walk away with clarity and value either way.