It is not uncommon for long distance or endurance Triathletes to struggle with an increase in body weight during the peak of training season. It can be very frustrating to put in endless hours of swimming, cycling and running only to see the number on the scale go up instead of down.
In fact, there are athletes who embark on the endurance journey simply to lose weight and are rudely awakened when that doesn't happen. I even see marathoners and half marathoners gain weight during training. Unfortunately, these athletes are not looking at the big picture. In some cases, they may have been given misleading information about nutrition and hydration. If this has happened to you, or if you are thinking about signing up for an endurance event. Consider a few things before you also get caught in this trap.
First of all consider, the effects of carbohydrate intake and hydration. An endurance athlete typically requires slightly more carbohydrate calories than a non athlete. During digestion, carbohydrates are reduced to glucose particles. Glucose is utilized for energy to workout. What is not used is stored as glycogen for the subsequent training session. Glycogen retains a substantial amount of water, which is of great benefit to an athlete in terms of maintaining optimal hydration. It can also account for up to 5 pounds of total body weight. Since athletes are constantly in a state of glycogen usage and glycogen storage, this water weight can and should be maintained for the entire training season. The water weight enhances overall performance and the health of the athlete. Water weight can fluctuate daily, as well. So be mindful of it and know that there could be up to a 5 pound difference between a pre-run weight and a post-run weight. Both optimal levels of glycogen and water are key nutritional strategies to all endurance athletes.
Now, consider calories consumed. I work with Ironman athletes who workout up to 20 hours per week during peak season and marathoners who run 50-60 miles per week. There are some athletes who use training as an excuse to eat whatever they want – and tend to have a more difficult time obtaining their “racing weight.” This type of weight gain is called “fat gain.” They consume more calories on a daily rate than they are burning. For example, they may be burning 2000 calories during a 15 mile run and come home and eat a half gallon of ice cream with peanut butter, whipped cream and chocolate sauce, which totals 3500 calories (true story). Any excess calories consumed will ultimately be stored as fat. Athletes should be mindful to eat according to their activity level. And they must always balance healthy, nutrient dense foods with that training so that the nutrients can be utilized and not stored. Another example that I see often is the runner or cyclist who consumes a sports bar or a gel every 15-20 mins during exercise. I have even seen this in athletes who are going for a 60 min treadmill run. Most athletes do not require extra caloric intake during activity under 90 minutes. And if they training their metabolisms correctly to be efficient, consumption can be dropped way down and performance can be enhanced overall.
Next, look at the bigger picture. Are you running 40 miles per week and sitting for 100 hours per week? Consider the activity that you are involved in during the remainder of the day – not just training hours. A well-trained athlete can certainly use extra calories more efficiently than an untrained non-athlete, but weight gain is still possible (and common) in highly trained athletes and fitness enthusiasts who simply eat too many calories.
The final aspect to consider is the addition of muscle mass. Endurance training is going to involve building muscle mass. Luckily, it's a beneficial effect. Since endurance sports are aerobic, we are not talking about a large amount of muscle hypertrophy, like what we see in body builders, but simply a shift in body composition. This is more likely to occur in beginner athletes and those who are new to the world of endurance sports. And this typically only accounts for 2-3 pounds of overall body weight.
My advice is to seek out an experienced sports nutritionist or exercise physiologist and discuss the proper way to fuel for endurance training. Keeping regular track of your body’s response to endurance training via composition measurements throughout the season is an excellent way to provide you with the feedback you will need to make adjustments in your training, nutrition and hydration.