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The Triathlete’s Guide to Thyroid Nutrition

May 02, 2025

Nailing your training but can't shift those stubborn kilos? Maybe you’re battling gut issues despite a dialled-in nutrition plan or even dragging yourself through sessions after a solid 8 hours sleep.

If this sounds all too familiar, it might be that your thyroid has been flying under the radar.

As a sports dietitian, I'm seeing more triathletes pushing through these warning signs – constant fatigue, resistant weight, bloating, and mysterious gut problems – not realising there's a tiny butterfly-shaped gland in their neck calling the shots.

Thyroid health isn’t my area of specialty so today I’m joined by Registered Dietitian and Functional Practitioner, Alisha Knicely, to talk about about how this powerful gland affects everything from your race-day performance to your Monday morning motivation.

Diagnosed with an autoimmune thyroid disease in 2017 , Alisha’s drive to understand what was happening in her body was a turning point in her career. She now specialises in Hashimoto’s and Hypothyroidism and helps her clients to reverse the symptoms of thyroid dysfunction.

The Performance Powerhouse You're Overlooking

Your thyroid is your body's metabolic control centre. It regulates your heart rate, energy levels, and even how quickly you bounce back from those brutal brick sessions. For triathletes pushing their bodies to the limit, optimal thyroid function isn't just helpful – it's essential.

The Nutrient Trifecta

Want your thyroid firing on all cylinders? You need three key players: iodine, selenium, and zinc. But here's the catch – more isn't always better. Like race-day nutrition, it's about getting the balance right. Strategic food choices like seafood, organ meats, and nuts can deliver these nutrients without the risks of over-supplementation.

Red Flags You Can't Ignore

If you're experiencing:

- Unexplained fatigue despite proper rest

- Stubborn weight changes

- Slower recovery between sessions

- Mood swings affecting your training drive

It's time for a proper thyroid assessment. Don't guess – get tested. A comprehensive blood panel including TSH, T3, T4, and thyroid antibodies will tell you exactly where you stand.

The Overtraining Connection

Think you can push through anything? Think again. Excessive training without proper recovery can throw your thyroid into chaos. Those sleepless nights and persistent fatigue aren't badges of honour – they're warnings that your body needs a different approach.

Your Action Plan for Optimal Thyroid Function

Fuel Smart: Focus on nutrient-dense whole foods that support thyroid function
Guard Your Gut: Your thyroid depends on proper nutrient absorption
Manage Stress: Yes, that includes training stress – more isn't always better

Beyond the Basics

Living with a thyroid condition doesn't mean hanging up your tri suit. Whether you're managing Hashimoto's or just optimising your performance, it's about working with your body, not against it. Regular monitoring and professional guidance can keep you racing strong.