Thyroid UK
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Hypo and losing muscle whilst low carbing and exercising

Hello Everyone, wondered if anyone could shed any light on this.

I'm currently taking 75mg levo and have been hypo since around 2011. I still have symptoms of fatigue, freezing cold feet and hair loss although since doing more research I'm taking supplements which I think are helping.

My question is more related to diet and exercise though. Since Oct 2014 I've been working out twice a week, cardio and weights and follow a gluten free and low carbohydrate diet. I had a body composition scan done when I first started the gym and a repeat one recently.

The results were quite surprising, in 6 months of weight bearing exercise and fairly strict diet I had stayed exactly the same weight (understandable with hypo) but had actually lost muscle mass - about 3kg. I suppose the reason why I was so surprised was because I felt and looked a lot more toned.

I did a fair bit of reading after my second scan and realised the low carbing really wasn't helping me so have upped my carbs a fair bit whilst still following a wheat free diet.

Does anyone else have any experience of this? Is hypothyroidism renowned for decreasing muscle mass? I'm generally quite confused about what to eat anymore. Low carb certainty helped my IBS but the crushing tiredness wasn't a welcome side effect.

4 Replies

Are you making sure you are getting enough protein, particularly after exercise? That is really important. If you are doing weights they will need to be reasonably heavy to build muscle mass and you will definitely need a decent amount of protein to enable that to happen. It is also quite difficult to build muscle mass if you are eating at a calorie deficit.

Were both scans done at the same time of day on the same scanner? Our hydration levels can change during the day and this can affect the measurements. Also some types of machines are more accurate than others. What sort of scan was it?

The chances are that if you are looking and feeling more toned then you probably are. I still personally feel the best way to get an accurate idea of your body composition is actual measurements of various parts of your body and use callipers correctly to work out fat percentage. Just comparing measurements of your chest, waist, hips, thighs and upper arms can tell you something about how your body composition has changed.

As for low carb diets, they don't suit everyone. Certainly reducing refined carbohydrate and sugar intake is a good idea and will probably help your IBS but cutting back too far on carbs while you are exercising can have a detrimental effect. I used to be able to follow low carb diet and just feel a bit off for a few days at the beginning. Now if I try I can't function. Rather than worrying about how much carbohydrate you are eating, perhaps just look at the quality of the carbs. Avoid processed carbs and sugars and go for natural ones. Also perhaps try increasing the amount of protein you are eating rather than decreasing the carbs. You will probably find your carbohydrate intake will drop slightly when you do this anyway. Just be careful not to go overboard with the protein intake. It might be worth doing some research into this area to find a protein goal suitable for you and your exercise regime.

Being hypo can make all this harder. Just remember to make small changes that aren't going to compromise your health and you should be fine. It sounds like you have done a great job of increasing your health and fitness through exercising though :)

Carolyn x



It is because you are undermedicated.

Your muscles are one of several major targets for thyroid hormones to do their job, especially those which are used for prolonged effort (your slow-twitch muscles). T3 is especially important so when only medicated on T4 you may not be getting enough T3 actively transported into your muscles.

To reverse inherent muscle wasting you need to increase your med dose or add T3.

For many weight loss happens naturally when TSH is suppressed.



If you are exercising hard, your muscles will take up glycogen (they need it) so you can usually afford to increase carbs without adverse effects. If you read Dr Malcolm Kendrick's bog he has a nice article about How Sumo wrestlers put on weight without getting diabetes - I know you don't want to put on fat, but it explains how carbs and fat are processed. You have to burn something and often protein (muscle) is easier to burn than fat.

Cardio can be catabolic, T3 definitely tends to reduce muscle mass unless you are eating a lot and training really heavy. I was a bodybuilder in my younger day, BTW.


Thanks for the comments. Lots of things to think about. I have changed my work out recently to reduce cardio and increase free weights. Hopefully that should help.

I will also up my protein post work out.

The scanner used should be fairly accurate and I did test first thing and fasted but the second time I had just completed a two week low carb 'boot camp' clearly that is not the plan for me.

I may well be under medicated but my GP won't re-test for a few months.

The fatigue is also exacerbated by a very lively toddler. Roll on September and the start of pre-school!


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