Eating more calories than you need. I would say this is the most common reason why you gain weight while training. Many runners "reward" their hard, long efforts with a huge meal because they think they've burned a butt load of calories (that's a scientific term, I might add). Generally speaking, you burn about 100 calories per mile you run. Some people burn more, some less, so this is a general estimate. If you run 10 miles, you burn roughly 1000 calories. That's great, right?? Well, you also probably drank 16oz of sports drink, maybe more. Depending on the sports drink, that could be 200 calories. So now we're down to 800 calories burned. Over the 10 miles, you may have had a gel or some chews. One gel is usually around 100 calories. So we're looking at about 700 calories burned. That's not bad, but when you and your running buddies hit up the breakfast joint after your run, chances are high you're taking in more than that with your eggs, bacon, toast and coffee with cream. Heck, sometimes just a smoothie alone can be well over 500 calories. I'm not saying you shouldn't eat after your runs. I would never say that. What I'm saying is you probably don't need to (and shouldn't) eat as much as you think you need after your runs. It's better to have something small that's mostly easily digestable carbs (like fruit) and a small amount of protein (something like a serving of nut butter, which is 2 tbs) right after your run. Then an hour or two later, you can have a larger meal, but again, you don't need a monstrous amount of food. The best thing to do is opt for nutritionally dense foods - things that are high on nutrition and low on the bad stuff. I know this isn't all that fun. If you really want to have that pizza or other not-so-good choice, that's ok as long as the majority of what you eat is good food. The best thing you can do is determine what your calorie needs are, along with the specific amounts of carbs, protein and fat you need to fuel your workouts, recover from those workouts and maintain, or even lose weight, along the way.
You store more glycogen. Part of long distance training involves training your body to use various sources of fuels more efficiently. As you move along in your training, your body gets better at storing glycogen. Before you started running longer distances, you didn't really do many activities that depleted your glycogen stores. With runs that are over 90 minutes, you're using up much of your glycogen. And over time, your body has gotten better at replacing that glycogen store. But keep in mind, when you store glycogen, your body stores water along with it. This can add numbers to the scale, which is most often seen during the taper period before your race. Less training and more carbs can lead to a little weight gain. But that's a good thing and will most likely be gone once the race is over.
Mistaking thirst for hunger. Many of us have a hard time keeping up with our hydration needs. Add hundreds of miles, some of them intense, and you may be constantly in the dehydrated zone. Unfortunately, our mind can play tricks on us and tell us we're hungry when we're actually thirsty. Staying on top of your hydration, all day, everyday, can help prevent this from happening. The Institute of Medicine recommends the average male take in 3.7 liters of fluid a day and women take in 2.7 liters of fluid a day. This is for the average male or female, mind you. Long distance runners will need to up these amounts based on their specific needs. You can use your urine color as a guide: your urine should be light yellow by lunch time and stay that way for the rest of the day.
Building muscle. I'm sure you've heard the saying that muscle weighs more than fat. As you get into your training, you are building muscle with every run. You probably have noticed more tone to your legs and even your abdominals. If you've added strength training, hill runs or other cross training activities, there's no doubt you're building muscle. This is a case where the number rising on the scale isn't a bad thing and you should pay more attention to how your clothes feel.
What's helped me the most in preventing weight gain, and even losing weight, while long distance training is keeping a food log. It can get tedious and be a pain in the butt at times, but it's the best way to know how many calories you're eating vs. how many you're burning. You can also keep track of your macronutrient intake (carbs, fat, protein) as well as key micronutrients such as vitamins and minerals. There are hundreds of food logs out there. I like MyFitnessPal as a food log because its database is awesome and a lot of what you eat is probably already entered, saving you time. You can also scan your foods and have the data entered that way. MyFitnessPal is also great because it can link to many tracking tools such as FitBit and others. Keeping track of what I was eating on NON running days really helped keep things in check.
Before you go fiddling with your calorie intake, first you'll need to know your basal metabolic rate, which tells you how many calories you need to take in just to be alive. Sometimes not even eating this amount can cause weight gain because your body thinks it's starving and won't burn as many calories throughout the day so it can conserve energy. So you need to eat at least as many calories indicated by your BMR. But for distance runners (any athlete, really), it goes beyond the BMR. You need to determine what your calorie needs are to maintain your weight at your current activity level. From there, you can try to create a deficit to lose weight, if that's your goal. It gets confusing and a lot of online calculators can vary in their accuracy. I'm always available to help you determine what your calorie needs are and how you can create a calorie deficit without missing out on the nutrients you need to fuel your workouts. So, to wrap things up, here are the things you can do to help keep the pounds off as the miles go up:
- Track your food intake. This is the best way to see what you're eating, track your calorie intake and create a deficit if necessary.
- Don't reward yourself with food. Buy new gear, get a massage, whatever. Don't reward yourself with crappy food all the time.
- Stay hydrated as much as possible.
- Don't go too long in between meals so that you don't overeat when you do eat and you can keep your metabolism firing for longer periods of time.
- Don't be a slave to the scale. Go by how you feel and how your clothes feel.