Dangers of running Underweight + Injury

Hi everyone,

I'm 19 and have been running seriously for a year. I ran my first half-marathon two weeks ago in 1:42:03 and was thrilled as I had trained really hard, been strict in terms of eating healthily, only drinking a couple of beers a week, and training hard: running five-six times a week, often 43 miles. This regime saw me at the start line weighing 9-9.5 stone. I'm pretty much 6 ft, and according to BMI (17.95) I'm underweight. My parents are concerned as I've just finished my first term at university and I was just wondering if there's anyone out there who knows if there are any dangers of running while underweight? It definitely doesn't seem to have stopped any of the other runners I train with on the track- they look anorexic practically!

I have struggled with an unhealthy obsession with food and exercise (faddy celebrity diets etc), along with quite low self-esteem despite being naturally skinny and an ectomorph. Since my half-marathon, I've not been able to run consistently and have found it difficult to appreciate Christmas and being with my family and celebrating! I know I need to gain weight and learn to enjoy myself but I'm scared of losing fitness, getting fat etc. I'm facing a weeks layoff with ITBS, and am concerned about losing fitness- during training I ran 15 miles numerous times so I guess I'm in a pretty good place.

Sorry to keep going on, but if there's anyone who has experienced something like this I'd greatly appreciate a helping hand! Thanks, Ben


  • You are underweight and have an unhealthy relationship with food.

    Those two things suggest to me that you need to seek advice from a doctor first and foremost. 

  • I'm not sure I can help much but can sympathise to some extent. I've been on loads of diets in the past few years including slimming world, fasting, low-carb despite never having a bmi above 21. I've also gone through times when I've forced myself out for runs due to being worried about losing fitness or gaining weight even when I was exhausted or injured.

    Personally I found that my doctor was not that bothered when my BMI was in the 17-18 range, just saying that they had seen much worse and told me to try to eat a bit more. Hopefully your GP would be more sympathetic if you spoke to them.

    When I find myself slipping into that mindset, I try to remind myself of why I run and control what I eat, its to be healthy, not to be the thinnest I possibly can. Some people are naturally very thin, I'm not and for me it's not healthy so I try to be rational and remember that it's not worth sacrificing my long term health for a number on the scales or a big number of miles in my training log! I don't want osteoporosis or heart problems or any other problems as a result of my self-enforced regime!

    Secondly, I find I actually run better with a BMI of 19-20 rather than 17-18 as I have more energy to train and feel much stronger. I also feel much better emotionally - less stressed, less tired and more motivated to go out and run.

    I don't mean to make it sound easy, I know it's really difficult and even after 4 years I find myself still slipping back into that mentality fairly frequently. A slight Christmas weight gain is causing me disproportionate worries at the moment!

    Good luck!

  • The BMI is not outrageous for a male distance runner, and a young one at that, particularly after a long training block, coming up to a race. Provided you are healthy, have a balanced diet, and are taking in enough food so your weight is not dropping, then the sad fact is that low weight will contribute to faster race times. A few more kgs won't affect things too much, and you can maintain fitness carrying a bit extra. At this time of year I am carrying about 4kg more than when I will race next. I'm not worrying about it as I feel in control.

    If you are getting a bit obsessional over diet then one approach is to direct this in a positive way. There seems to be a real disconnect between your running and diet (e.g. Following celebrity diets). Try tying them together, making sure the diet is fit for purpose.

    If diet really is a mental health issue then you need to address it. As you would only get a few minutes of a Doctors time be prepared to be frank about the issue and what support you need. 

    Be aware that non runners often comment that slim endurance athletes are looking unwell / need a good feed,  often when there is nothing wrong with them

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