46. Low Carb Is Wrecking Your Thyroid (And Most People Don't Know It)

Many people struggling with fatigue, weight gain, brain fog, or low libido may actually be dealing with thyroid dysfunction — and not even know it.

In this episode of Healthy AF, Zane explains how common lifestyle habits like low-carb dieting, intermittent fasting, overtraining, chronic stress, and sleep deprivation can quietly disrupt thyroid function and slow your metabolism.

You'll learn why markers like T3, reverse T3, and TSH matter more than most standard lab panels suggest, how the body adapts to low energy availability, and why many people with thyroid symptoms are often told their labs look "normal."

Zane also breaks down the role of insulin, leptin, liver glycogen, and carbohydrate intake in thyroid hormone conversion — and why reintroducing the right foods can often restore metabolic function.

If you've ever struggled with low energy, stubborn weight gain, cold intolerance, or declining performance despite dieting and training harder, this episode will help you understand what may really be happening inside your metabolism.

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Supportive research

Low carb diet increases incidence of REDs and low T3⁠
https://pubmed.ncbi.nlm.nih.gov/40639795/%E2%81%A0
⁠
Low carb diet reduces T3 in athletes⁠
https://blogs.bmj.com/bjsm/2023/08/14/a-bad-situation-made-worse-low-carbohydrate-intake-amplifies-low-energy-availability-hormonal-disturbances/⁠
⁠
Low carb diet induces low thyroid function⁠
https://pmc.ncbi.nlm.nih.gov/articles/PMC11558958/⁠
⁠
Keto diet reduces thyroid function⁠
https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0269440⁠

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00:00 – Introduction: Thyroid Health and Metabolism
00:40 – Remembering Charlie
02:00 – Common Symptoms of Low Thyroid
03:30 – How Thyroid Affects Metabolism and Energy
04:30 – Hormonal and Cardiovascular Effects of Thyroid Dysfunction
05:30 – Why Thyroid Issues Often Go Undiagnosed
06:30 – Stress, Overtraining, and Aggressive Dieting
08:00 – How Thyroid Hormones Work (T4, T3, Reverse T3)
09:40 – What Low-Carb Diets Do to Thyroid Function
11:00 – Low Energy Availability in Athletes
12:30 – Why Your Body Interprets Low Carb as Scarcity
14:00 – The Impact of Fasting on Thyroid Hormones
15:30 – Liver Glycogen and Overnight Stress Hormones
17:00 – Why High Performers Are Vulnerable
18:30 – Insulin, Leptin, and Thyroid Signaling
20:00 – Optimal Thyroid Lab Ranges Explained
22:30 – Why Symptoms Matter More Than "Normal" Lab Ranges
24:30 – How Thyroid Issues Affect Testosterone in Men
26:00 – Insulin Signaling and Thyroid Conversion
28:00 – Low Carb vs Insulin Resistance: Different Labs, Same Symptoms
31:00 – Why Leptin Is the Missing Link
33:00 – Reintroducing Carbs to Restore Thyroid Function
35:00 – LDL Changes After Increasing Carbohydrates
36:30 – Body Temperature and Metabolic Rate
37:30 – Training, Recovery, and Sleep
38:30 – Best Carbohydrate Sources for Thyroid Health
41:00 – How Much Carbohydrate You Actually Need
43:00 – Macro Ratios for Fat Loss vs Performance
45:00 – What Indigenous Diets Teach Us About Metabolic Health
47:00 – How Ultra-Processed Foods Disrupt Energy Production
49:00 – The Real Cause of Fat Gain and Metabolic Dysfunction
51:00 – Why "Calories In Calories Out" Misses the Real Problem
53:00 – Fixing Metabolism Through Food Quality and Energy Availability