Managing Underactive Thyroid and Hashimoto’s: A Nutritionist’s Perspective

Understanding Hashimoto’s Thyroiditis and Hypothyroidism

Hashimoto’s thyroiditis and hypothyroidism exert much of their impact through the underproduction of thyroid hormones [3],[5]. Still, it is the way they disturb core physiological functions that often leads individuals to seek medical help.

The thyroid gland, located at the base of the neck, plays a pivotal role in maintaining metabolic harmony [6]. It releases hormones such as thyroxine (T4) and triiodothyronine (T3), which regulate cellular metabolism, growth, temperature, and energy levels throughout the body [6].

As production of thyroid hormones declines, a cascade of symptoms and health risks starts to unfold. For some, the changes are subtle at first. For others, symptoms develop gradually over months or even years, making them easy to overlook until they significantly affect day-to-day life.

Recognising the Symptoms of Hashimoto’s Thyroiditis and Hypothyroidism

Early-stage symptoms are frequently subtle or even absent, with many individuals unaware of the underlying dysfunction. Over time, however, the body’s systems begin to respond to the low levels of circulating thyroid hormones.

Fatigue becomes an ever-present companion, unresponsive to rest or lifestyle modification [7]. Individuals also may notice unexplained weight gain, a persistent chill even in warm environments, and pronounced dry skin [8]. Hair loss, brittle nails, and noticeable puffiness – particularly around the face and eyes – may develop as the hormonal imbalance progresses [8][9].

Gastrointestinal disturbances, such as constipation and indigestion, are common, as the slowing of metabolism affects every organ system [10]. Muscles and joints may ache or become weak [8], and the heartbeat slows – sometimes to an extent that disrupts normal cardiac function [3]. Cognitive changes – sometimes termed ‘brain fog’ – are also frequent, ranging from forgetfulness and poor concentration to outright depression or anxiety [11].

Chronic inflammation caused by Hashimoto’s thyroiditis, in particular, has a wide-ranging effect – not only reducing thyroid hormone output but also increasing overall susceptibility to other autoimmune diseases. These may include vitiligo, rheumatoid arthritis, type 1 diabetes, Addison’s disease, pernicious anaemia, and multiple sclerosis, highlighting the interconnectedness of immune dysfunction [12]-[17].

For women specifically, menstrual cycles may become irregular or abnormally heavy, while fertility can be impaired [8][18]. And in children and adolescents, slowed growth and delayed puberty may signal an underlying thyroid condition [19].

Complications related to untreated hypothyroidism are serious and include high cholesterol, elevated cardiovascular risk, heart failure, myxedema (a rare, life-threatening state), [3][20] and, particularly in pregnancy, risks to both mother and child. Symptoms must be taken seriously and addressed proactively [21].

Making Nutrition Part of Management

Today, a nutrition-focused approach is widely recognised as a critical adjunct to medical therapy in hypothyroidism and Hashimoto’s thyroiditis, providing meaningful benefits that go beyond symptom control.

Although medication remains the mainstay of treatment, growing clinical consensus highlights that well-considered dietary choices and nutritional repletion significantly impact both short- and long-term outcomes.

A body of research demonstrates that key micronutrients – including iodine, selenium, vitamin D, vitamin A, iron, and zinc – function as cofactors in thyroid hormone production and tissue repair [22]. Even marginal deficiencies in these nutrients can impede metabolic function, intensify symptoms, or slow recovery, especially when left unaddressed over months or years.

Dietary planning begins with understanding individual dietary habits and identifying possible nutritional pitfalls. For example, in areas where iodine deficiency is still found, inadequate intake can exacerbate hypothyroid symptoms or reduce the effectiveness of medication [1]. Conversely, excess iodine might worsen autoimmune thyroiditis for those with Hashimoto’s, particularly for highly susceptible individuals [1].

A focus on whole, minimally-processed foods – including colourful vegetables, nuts, seeds, fish, and lean meats – enriches the diet with antioxidants and essential fatty acids, further reducing chronic inflammation linked to autoimmune flares. High-fibre choices, such as oats, lentils, chia seeds, and fresh produce, are particularly useful (when tolerated) in mitigating constipation, a common issue in hypothyroidism [23].

These dietary strategies also aid in sustaining balanced blood sugar and energy throughout the day, which is crucial as many affected individuals struggle with persistent fatigue and unintentional weight gain.

Applying Nutritionist-Led Dietary Strategies and Lifestyle Adjustments

Yet effective management of Hashimoto’s and underactive thyroid rarely follows a one-size-fits-all blueprint. Instead, a personalised, nutritionist-led strategy is needed to support optimal health and day-to-day functioning.

At the outset, this approach involves a detailed dietary and lifestyle assessment alongside a comprehensive review of blood tests and appropriate functional medicine tests, if appropriate, including gut microbiome or nutrient panels. Identifying and correcting micronutrient gaps – most commonly, low selenium, vitamin D, iron, or B12 – addresses reversible contributors to ongoing symptoms and sets the stage for metabolic improvement.

Nutritionists also help patients navigate confusing food advice by explaining why certain exclusions may help some, but not all, patients. The aim is to build a diverse and enjoyable dietary pattern that supports gut health, immune function, and emotional well-being.

Studies show that interventions such as elimination diets (gluten or lactose-free), energy restriction, and supplementation with nigella sativa (a black seed) were associated with improved thyroid antibodies and hormone levels in people with Hashimoto’s thyroiditis, with the greatest benefits seen in programmes tailored to individual deficiencies and needs [24].

Meal planning, mindful eating techniques, and tips for food preparation are key components of ongoing support. Simple swaps – like increasing oily fish for omega-3s, reducing processed foods, or preparing cruciferous vegetables by steaming – help patients balance benefit and risk without unnecessary restriction [23].

Meanwhile, other studies have found that adherence to a Mediterranean diet, when followed for 12 weeks by women with Hashimoto’s thyroiditis, improved thyroid disease activity markers and contributed to weight loss – even when participants remained on their usual medication doses [25].

Lifestyle modification, closely linked with dietary adjustment, completes the holistic picture. Low-impact exercise not only counters fatigue but also preserves muscle mass, reduces cardiovascular risk, and has been shown to improve psychological resilience in thyroid disorders [26]. Good sleep hygiene helps address the sleep disruptions that many with thyroid dysfunction experience. And stress-management practices, like meditation, guided breathing, or yoga, are strongly encouraged throughout daily life [27].