A question came up recently about weight gain during marathon training. Many new runners training for a marathon are confused about why they would gain weight while running all those extra miles. I have a few theories about why this is happening.
1) Most people overestimate the calories they burn on a run. The amount of calories you burn depends on your weight, gender, lean muscle mass, and intensity and duration of your run. The Garmin 405 cx watch will calculate how many calories you burn based on your hear rate during a workout. This is slightly more accurate than just using your gender and weight. It is known that the faster you run the more calories you burn. So someone running for an hour at a 6 min mile pace will burn more calories than someone running for 2 hours at a 10 min mile pace.
2) Newer runners will experience increasing muscle fiber recruitment, strengthening of tendons, and increasing bone density all of which contribute to extra weight. Newer runners or runners increasing their mileage also experience increases in muscle glycogen storage. For every gram of glycogen that is stored, 2-3 g of water is stored along with it.
3) There is an increase in plasma volume. This translates to extra weight as well.
4) Many runners have very detailed training regimens, but have absolutely no nutrition plan. This can lead to over consumption of calories and/or not combining macronutrients (carbohydrates, protein and fats) appropriately.
5). Many new marathoners believe that they can eat whatever they want because of all the mileage. Not only can this lead to weight gain, but it also can lead to poor recovery in between workouts and minimized training effects.
6) The other phenomenon I have seen is that a runner, in an effort to lose weight, will under consume calories. This runner's metabolism slows down and the runner gains weight or struggles to lose weight.
7) There are lots of myths associated with eating for marathoning. One that comes to mind is the big pasta bowl eaten the night before a marathon. Although pasta can be part of a healthy diet, it is usually covered in high fat sauces. There are many other healthier carbohydrate options that you can consume on a daily basis leading up to a marathon - not just for one pre-race meal.