Weight Loss NHS

Undereating effects

Hi all

I've been struggling for a number of years with a variety of symptoms, mainly tiredness related. This hit rock bottom about 18 months ago when I crashed - felt awful, no energy, yet with no diagnosable cause. Blood tests were ok apart from a slight B12 and vit D deficiency which have now been rectified. Drs were keen to diagnose me with depression and chronic fatigue, and gave me a 6 month course of fluoxetine which worked for the depression but extreme fatigue remained. I was convinced that something was actually wrong and pushed and pushed for more tests. I was sure it was thyroid related as the symptoms were scarily accurate to hypothyroid but tests said it was fine. I have since been trying all sorts of supplements (mainly sports and vitamins) and extra protein and can function quite well, even managing to train at the gym quite hard multiple times per week. But I'm far from well and am constantly exhausted. Weight hasn't budged despite exercise and I sleep a lot, going to bed mega early and having no energy past about 8pm.

At Christmas I was given an Apple Watch which records my daily activity and sleep, and I was surprised to learn I burn around 700 calories per day through normal activity and exercise. Combined with my supposed BMR of 1800, I should eat around 2500 calories to just maintain my weight. Curious I did a full food diary for a week and found I was consistently under eating by at least 500 calories, sometimes more. With exercise this results in around 1300 calories per day, less than my BMR. No wonder I'm tired! Sleep was actually very good, getting over 8 hours with only a small percentage classed as 'restless'.

So my questions are:

1. What could the effects of eating this little over a period of time do to me? I hear of metabolic damage but is that an actual thing?

2. How do I recover? I'm now eating more, trying to hit 2500 calories daily, but I'm not used to eating large amounts so am slowly working my way up to it.

Many thanks


3 Replies

Hi Steve,

As none of us here are medically trained and as you've obviously been seeing doctors about this tiredness you've been experiencing, I would suggest that you go back to them, with your findings.

It may be that with this extra knowledge, they'd be able to run different tests to rule out any long term damage and offer advice on the best way forward for you.

I hope that you get everything sorted to your satisfaction :)


Our bodies are very adaptable. If you've been under eating for a while, your body won't want to expend energy. The term 'metabolic damage' isn't a very helpful term, have a look at 'adaptive thermogenesis' instead.

As you are increasing your food, make sure it's nutritionally dense with lots of good quality protein. Don't overdo the exercising. If there isn't an improvement in your health, then you obviously need to go back to your doctor. Perhaps check out chronic fatigue syndrome symptoms too.


Hi, I use a weight loss website, but "background calories" are deducted from any exercise. "Background" calories are the calories that you burn through breathing - the calories your body burns if you just sat still and didn't move.

I don't have experience of an Apple Watch (I clearly wasn't good enough for Santa to bring me one... :( ) BUT I do have experience of using a heart rate monitor to be able to identify the calories burned through exercise.

Just check that you don't need to remove these, before you add the calories to your intake.

Hope this makes sense!


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