Yesterday, reading in my newspaper I discovered an interview with a professional boxer (at the end of his career). He said preparing for an upcoming fight has been really hard... getting body weight down and all that.

What caused my surprise was another remark from the boxer. When he is well-trained, low weight, he has a really low body fat values of, say, 5%, but he does not really like this. He said that during this time, he is easily irritated, exhibits uncontrolled anger and tends to be a more unloveable person.

So is this an individual trait or can this be generalized? So getting low body fat could have undesirable effects on the temper or mental state of the athlete? Is there a medical explanation for this? How would a sports-psychologist comment on that?

  • reading this after 6 months, I think the 5% value I mentioned in the text was just guesswork. I think I meant to say 10%...whatever value is targeted minimum for professional athlethes. (I don't want to edit the post).
    – knb
    Jun 29, 2012 at 12:06

2 Answers 2


Yes. Undereating, especially not eating after vigorous exercise will drive up your cortisol levels and put you in a bad mood. Without enough carbs your body will have trouble producing serotonin (the well-being neurotransmitter) and you will not feel energetic.

5% is about the minimum you should have, it is unhealthy to go that low. Do you think you would feel good if you forced your body fat percentage to it's minimum?

  • 5% is about the minimum, but it isn't really unhealthy. You just have to pay very close attention to diet. It's below the 5% range where it's unhealthy to maintain for more than a day or so. Most elite athletes will fall in the range of 5-10%.
    – JohnP
    Jun 29, 2012 at 14:55

There's no reason to assume from this that it's the low body fat. Cutting weight sucks. It's miserable. You're eating stuff that tastes nasty because you only want very specific foods. You're avoiding stuff you normally love eating that everyone else around you is eating. On top of that you're nervous because of the upcoming fight.

Anyone would be irritable under conditions like that, even if they're starting at 15% bodyfat and cutting down to 10% to make the weight class.

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