Does a Low Carb Diet Cause Hypothyroidism?

I have been diagnosed with hypothyroidism (TSH 11.55) and am currently taking 50mcg of Synthroid  Would this interfere with reaching ketosis? Could my low carb diet have brought on hypothyroidism?

A: The only way that a low thyroid would affect ketosis would be terribly indirectly. The development of ketosis is dependent on two things:

1. That liver glycogen is depleted. I can’t see how low thyroid would affect this.
2. That there is adequate free fatty acids available. A low thyroid level might affect this but since you’re on replacement synthroid (which should bring your T4 and T3 back to normal levels), I don’t think it will matter too much.

Low carb diets to lower levels of T3 (active thyroid) but TSH (thyroid stimulating hormone) levels to not typically drop. The drop in T3 with normal TSH and T4 (and increased reverse T3 or rT3) is called Euthyroid Stress syndrome (ESS) which is distinctly different than true hypothyroidism (indicated by low T3 and low TSH).

About the author

Lyle McDonald

Lyle McDonald+ is the author of the Ketogenic Diet as well as the Rapid Fat Loss Handbook and the Guide to Flexible Dieting. He has been interested in all aspects of human performance physiology since becoming involved in competitive sports as a teenager. Pursuing a degree in Physiological Sciences from UCLA, he has devoted nearly 20 years of his life to studying human physiology and the science, art and practice of human performance, muscle gain, fat loss and body recomposition.