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Thyroid UK
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Weight gain when hypo

This has been talked about a lot but I haven't found any explanation of where the excess weight "comes from", providing calories aren't increased? It goes against the basics of thermodynamics, doesn't it? I know that some weight is retained fluid but surely not all of it and not permanently! If you couldn't tell, I'm incredibly frustrated with my body for putting on weight, diagnosed 8 weeks ago and on 75mcg Levo currently. Last bloods showed ft4 and 3 in the lower range (which prompted an increase from 50mcg). I'm down to 2 work dresses to wear and don't want to leave the house because of how I look. I just want to cry.

6 Replies

Oh, forget thermodynamics! When you're hypo, all the supposed rules of science go flying out the window!

It most certainly can all be water. And permanently. The water is held by a substance called mucin, which doesn't let it go easily.

If you're talking about the laws of science, it's isn't physically possible for people to put on 14 kilos of fat in one month, either. But it is possibly to absorb 14 kilos of water very quickly, just like a sponge. Which is why people can gain weight so rapidly if they have a dose reduction, or something like that. My doctor's reaction when this was explained to him? There must be something wrong with the scales! lol


Thank you for the explanation - I had no idea water weight could be permanent. Do you know if there is a level of T3 at which weight loss isn't possible? And what can be done to minimise the water retention - is it just to drink more water?

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I don't think it can be regulated by how much water you drink. I wish I knew what one could do to minimise it. Because it's not the water the problem, it's the mucin. And I think you can only do anything about that by optimising your T3 level.

Any level of T3 that isn't optimal for you, will stop you losing weight on a sustainable basis.


Don't go mad on drinking water - too much can be as bad as too little.


The laws of biology are definitely not the same as thermodynamics. Biology seems to have far more non linear relationships.

However as well as the weight gain from water your basal metabolic rate (how many calories you burn if you did nothing) reduces. This is why we feel cold, because our bodies are not burning the calories to keep us warm. So, you can stay on the same calorie intake, do the same amount of exercise as before you were ill and put on weight.

I have lost weight, a little on levo, more on ndt. I stopped dieting and eat proper food, meat, veggies etc but all fresh and from local farms. I also drink full fat raw milk and eat butter etc. I mainly low carb.

Endo prescribed metformin in Feb and that's really helping.

Good luck


I hope they're keeping an eye on your B12 levels while you're on Metformin!


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