If you do take up competitive endurance sports, you probably will find yourself losing weight pretty quickly. A hard run or spin class may even make you feel sick to your stomach. Just stand near the food tent after any large endurance event and you will see more than a few athletes upchucking their post-event snacks. When your body is in a great deal of pain, you may end up vomitting. Oprah Winfrey has famously given her audience members advice not to eat after 5PM, but don't do this is if you are a working mother, who also works out. You need to be strong enough to also take care of your children! Especially don't severely limit your calorie intake if you are training for something as lengthy as a half-marathon.  If your body mass index falls into the lowest range of a healthy weight for your height, you are probably actually underweight because muscle weighs so much more than fat. A 5'5" 100lb model who doesn't work out much might be physically o.k., but a 100lb triathlete of the same height and weight is bound to eventually get sick and injured. If possible take your time eating after your workout and enlist a friend, neighbor or your partner to help with the childcare so that you can relax and eat a proper healthful meal like a salad with lost of protein sources in it and a slice of veggie pizza.