Whatever damn size they want. End of answer— kidding, kind of. This is a challenging question that comes up a lot in life, not just athletics. Everywhere you look there is a new idea about how to lose weight, be fit or look a certain way. It is easy to get caught up into thinking that certain body types may serve runners better. Often runners are under the misimpression that being smaller or leaner will help them get faster. In reality, the size that you should is predetermined in your genes. Your body size and shape will be the one that your body naturally rests at when you are eating the right amount of the right types of food for your body. You get to this point through trial and error as well as honoring what your body is asking for.
When you are fueling correctly and your blood work is good, this means (most of the time) you are in the exact right spot. This will look 100% different for everyone, no one body is the same. If you are losing or gaining weight during training and are not trying to, it might be a good idea to consult with a sports nutritionist and confirm that you are getting the nutrients you need to meet your maximum potential.
It is easy to look at other runners’ bodies and get caught in a comparison game. Thinking that a is going to beat you because s(he) is thinner, more muscular or just looks more like a runner is totally normal. However, these thoughts do not serve you and aren’t true. The healthier you are (feeding your self nutritional food and listening to your body), the better the runner you will be. No matter what your brain may tell you about how you look in moments of doubt or weakness, your body as it carries you through your miles is the right body for you – as long as you are treating it well. Most of the time, the body isn’t the problem, self-esteem is.
The good thing is that you can improve your relationship with your body and learn how to accept it and (gasp) eventually love it! It may not be a perfect relationship and you will still have moments of not liking your size, but learning to be thankful for your body’s acceptance of your goals and all the miles you put on it is the first step in honoring yourself as a runner. The more you can use positive self-take, the more you can appreciate all the hard work your body puts out for you.