The combination of a lot of running and not consuming enough calories often causes dysfunction (irregularities) of the menstrual cycle, leading to injuries.
Menstrual cycle irregularities (changing cycle lengths and not always having a cycle every month) and even not having a cycle at all (called amenorrhea) can occur with extreme, especially aerobic endurance, exercise.
If you don’t consume enough calories to counterbalance the large caloric expenditure of running, menstrual cycle irregularities can occur, which causes your body fat percentage to decrease. While decreasing body fat percentage is a good thing in most cases, in extreme cases it can become too low to support reproduction. When a woman’s physiological environment is not ideal to reproduce, the menstrual cycle shuts down.
Consuming fewer calories than what you burn, which causes inadequate nutrient intake, rather than the amount of running, is the main culprit of menstrual irregularities. However, running a lot triggers this imbalance between caloric expenditure and caloric intake, because if you don’t run, it’s nearly impossible to eat less than what you expend.
It may seem obvious to eat enough to support your running, but us women are under a lot of pressure — from society and often from ourselves — to look a certain way. Well, get over yourself, girlfriend! If you want to run a lot, you need to eat a lot. Period. You won’t gain weight if you’re running 50 miles or more per week. You won’t even gain weight if you’re running 30 miles per week. So run and eat! Your health and your running performance will both benefit.
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