Effect of low calorie diets on thyroid function

[Cooper27]

I've been listening to some interesting podcasts recently, which have touched on the effects of intermittent fasting on women. There are marked differences between men and women when it comes to fasting. Levels of Ghrelin (the hunger hormone) tend to be much higher in women than in men, and the higher Ghrelin is, the lower thyroid hormones tend to be.

Supposedly the issue is there regardless of whether you observe full fasting, intermittent fasting (although probably less so), or just a very low calorie diet.

I dug out this article:

ncbi.nlm.nih.gov/pubmed/234...

If I've read it right, it showed that women who follow a 1200 calorie a day diet will typically see their T3 levels drop by 40%, while those who were on a 400 calorie/day diet saw T3 levels drop by 66%!

When we first go to the doctor complaining of unexpected weight gain, the advice to "eat less" will make the thyroid worse. Additionally, if you restrict calories to limit thyroid related weight gain, then you may also compound your problems. It seems like a lose/lose situation

[greygoose]

That's exactly what it is. You need calories to convert.

[Cooper27 in reply to greygoose]

I've heard the vague mentions about starvation mode and slower metabolism before, but I've never heard anyone say that's why! It makes sense now Thanks!

[greygoose in reply to Cooper27]

You're welcome.

[AmandaK]

This makes perfect sense. The only thing that puzzles me is that those with diabetes and who are heavily overweight are being encouraged to go on an eating plan limited to 800 cals a day for three months. This seems to recalibrate the body and insulin levels and reverses the diabetes.

Surely this would play havoc with their T3 levels though? And with the slowing down of the metabolism, you would think that when they resumed a higher calorie diet that the weight would return.

The only example I can think of is MP Tom Watson who has lost a phenomenal amount of weight using this method of weight loss. However, the weight has not returned, which perhaps confirms the theory about ghrelin levels and gender (but why does it not seemingly affect his T3 levels?).

In my own case, the most successful diet was 5:2 intermittent fasting when I lost around 10IB and reached 68kg. Since 2015 (following mild concussion) I've not been well enough to resume this regime and my weight has rocketed to 77kg - I'm now the heaviest I've ever been.

BUT.... the literature about 5:2 states that intermittent fasting doesn't negatively affect the metabolism (can't source details presently) as it's the intermittent nature of it that prevents the damage.

I have wondered though if my low in-range FT3 levels have something to do with the 5:2 diet, even though I've not been on the diet when the levels have been tested. NB technically, I don't have hypothyroidism.

So yes, it's a double bind and it seems that women especially are at a disadvantage when it comes to trying to lose weight.

[Cooper27 in reply to AmandaK]

The podcast that brought this up did mention the diabetes diet, but I don't think anyone has monitored someone's T3 levels while they followed it. The thoughts were that the benefits for the diabetes tends to outweigh the risk to the thyroid though.

I'm unsure how 5:2 would differ from standard fasting. We all have occasional days where we eat less calories anyway, and I doubt the odd days make much difference to your thyroid health. I guess it's one to look at.

I think the next step is to see if T3 levels can improve again off their own back, or if the effects are permanent!

[AmandaK in reply to Cooper27]

Well the FT3 levels are consistently low over time - a bit of a mystery. So it might have nothing to do with the fasting. In fact, the first time FT3 was tested was in 2014 and this was well before I began the 5:2 diet: 3.14 (2.63-5.7). It was even lower in 2017 two years after I finished the diet: 3.86 pmol/L (3.74-6.11) but higher in March 2019: 4.08 pmol/L (3.74-6.11) though still not great.

[Cooper27]

According to this FAQ, trying to explain why lower T3 as a result of keto isn't an issue, supposedly lower T3 makes us Euthyroid, and may increase our lifespan *rolls eyes*

perfectketo.com/does-a-keto...

Proof that if you say something in a convincing enough tone...