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Marathon Training Can Make You Fat

Running and weight loss don't always go hand-in-hand.
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If you watched Shalane Flanagan, Meb Keflezighi, and other elites finish the TCS New York City Marathon earlier this month, you probably didn’t see much in the way of excess body fat.

Those lean physiques come from years of 100-mile-plus weeks of training and diet plans carefully mapped out by sports dietitians (not to mention superior genetics). Newer marathoners probably recognize they’re not going to look or perform like that after a single 20-week training program. But many are shocked to find themselves actually gaining weight as their training ramps up.


“It's emblematic—if I [told] you the last time it came up between me and an athlete, that would be yesterday,” says running coach and nutritionist Matt Fitzgerald, author of Racing Weight. North Carolina sports dietitian Susan Kitchen had literally hung up with a client dealing with the same problem moments before our interview. And New York-based dietitian Alissa Rumsey experienced this consequence herself when she trained for half marathons and one full marathon several years ago.

Surprisingly, they all say, marathon training isn’t actually a very good way to shed pounds. Preparing your body for the rigor of running 26.2 miles is one goal and slimming down is another; the two don’t go hand in hand as well as you might think. Taking on what Fitzgerald calls a “big exercise project” like a marathon while simultaneously holding a weight-loss target—or even just carrying around vestiges of a dieting-focused, restrictive mindset about eating—can backfire, leading you to pick up fat. How can this be, you might wonder, when you’ve always been told by the treadmill display that every mile run is about 100 calories burned?

For one thing, the math isn’t quite that simple, Kitchen points out. Not only are those numbers ballpark estimates that don’t fully take into account factors like sex and body composition, but they also change a lot based on the intensity at which you exercised.

Especially if you’re new to long distances, marathon training involves lots of mileage at a relatively easy pace, one at which you can carry on a conversation with your running buddies. (Fitzgerald emphasizes that even elite runners typically do only about 20 percent of their training at high intensities.)


In this aerobic zone, you’re teaching your body to burn its existing stores of fat for fuel, which you’ll need to run a successful marathon. However, that also means you’re not torching through that stack of pre- or post-run pancakes quite as quickly as you might think. And since you should be taking in fuel during your longest runs, you’re even less in the hole, calorically speaking, than it first seems, Kitchen says.

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Add to that our innate tendencies to reward ourselves for our hard work with indulgent but not very nutrient-dense foods and drinks like burgers, beer, and ice cream, and also to underestimate the number of calories we’ve consumed. (Not that we can be completely blamed on that second point—even food labels can be off by as much as 20 percent.)

And consciously or not, we also tend to move less the rest of the day when we’ve exercised a lot, Rumsey says. One University of Alabama study found women who worked out six days a week actually burned fewer calories overall than did women exercising two or four days a week, or even than they did during their sedentary days before the four-month research period. And another, in the journal Current Biology, looked at hundreds of people all over the world and found a plateau in total energy expenditure once people passed a moderate level of physical activity.

What’s more, exercise tends to rev up our appetite. This makes sense, since our calorie needs do change based on the amount of moving around we do, Fitzgerald says. But there’s a wide variation in this so-called compensation effect from person to person. It’s not always completely fine-tuned, especially if your diet’s not the most balanced or nutritious, making it easier to overeat. “You have people who—especially if their activity level passes a certain threshold from moderate to heavy exercise—their appetite just sort of runs away,” he says. “Unfairly, it seems to be more common in women.”


Many athletes exacerbate this effect by not eating enough before or after their workouts, a phenomenon Kitchen calls “athletic starvation.” Again, it runs a bit contrary to our intuitive understanding of calories in, calories out—but shorting yourself during these critical windows wreaks havoc on your metabolism in multiple ways.

First of all, if you head into a run—especially a demanding one like a long run or fast repeats on the track—on an empty stomach, you can’t push your body as hard. That means you aren’t burning as much energy in the first place, or triggering the kinds of changes you hoped you’d see in your endurance and strength. Immediately after exercise, your food is metabolized differently than the meals you shovel in while seated at your desk. Your body’s primed to use carbs and protein to repair muscle damage and replenish energy stores rather than to sock them away as fat.

You might not feel hungry, because hard efforts can temporarily tamp down your hunger hormones, Kitchen says. But if you don’t take advantage of this prime opportunity for recovery, you’ll pay the price later on. Your blood sugar will drop and your body will cry out for energy. Soon enough, you’ll find yourself rifling through the kitchen for the sugary, starchy items that’ll spike your blood sugar instantly.

While scarfing a bag of cheese puffs might work to keep you from passing out, it’s far from the best strategy for long-term success, she points out. You’ll feel hungry again soon after and likely overeat, especially if you’re still reaching for junk. Then, you might feel guilty and skip breakfast again the next day, kicking you off on the wrong foot all over again. This whole vicious circle stresses your body out, sending levels of the hormone cortisol (can prime your body to pack on abdominal fat) soaring.


Even if you have superhuman willpower than enables you to avoid bingeing later, you still can’t win. Though it’s “mind-blowing,” Fitzgerald says, eating too little overall can cause you to gain weight while marathon training. Here’s how that works, as best as scientists understand it: Running still does require more energy than slouching on the couch. If you’ve never been a big eater—or you significantly cut back on calories at the same time as increasing your mileage—your body recognizes you’re low on fuel and freaks out, slowing your metabolism to a crawl.

It’s similar to what happened to all those contestants from The Biggest Loser; follow-up research showed that, six years after their appearance on the program, they were burning an average of 500 fewer calories daily than would be expected for someone of their size. “One of the telltale signs that you’re making this mistake is that you’ll start to feel lousy in your runs,” Fitzgerald says. “It’s your body’s way of saying, ‘I’m not going to let you waste any energy, because you’re not giving me enough.’"

If general underfueling is your problem, you’ll have to take the leap of faith that eating more won’t make you fat, and try it. It might be hard to wrap your mind around at first, but as Fitzgerald points out, if you’re already gaining weight anyway you don’t have much to lose. But it’s far more likely you’re eating too much, he says. Fortunately, there are more nuanced strategies to address the issue than “just eat less.”


Start out by focusing on the overall quality of your diet; Fitzgerald offers athletes a list of higher-quality foods (vegetables, fruits, nuts, seeds, healthy oils, whole grains, dairy foods, and unprocessed meat and seafood) to eat more of and lower-quality foods to cut back on (refined grains, sweets, processed meats, and fried foods). More nutritious choices fill you up with fewer calories, so even if your appetite’s bigger, you’ll likely find it easier to keep your eating under control.

Making sure each meal includes all three macronutrients—protein, carbs, and fat—also steadies your blood sugar and controls your hunger throughout the day, Kitchen says. Start at breakfast, where many people overdo it on carbs and skimp on protein. For instance, eat a serving of Greek yogurt or a couple of scrambled eggs alongside your oatmeal with brown sugar and fruit.

In addition, pay special attention to fueling properly before and after a run. If you run first thing or it’s been hours since you ate, toss back something easily digestible—a banana, some toast, an energy bar—before you head out on a long or hard run. (And if that run lasts longer than two hours, you’ll also want to ingest some fuel along the way, either in the form of gels or other sports nutrition products or easily digestible foods like raisins or bananas—to the tune of 30 to 60 grams of carbs per hour.)

Within a half-hour afterward, reach for a recovery snack that has about 15 grams of protein and 30 to 45 grams of carbohydrates. Most people focus too much on the protein, “but the carbohydrate is what fuels the body to be able to use the protein for muscle repair,” Kitchen says. If you tend not to be hungry, try a smoothie with a fruit and yogurt or a scoop of protein powder, or time your runs so they finish around when you’d normally eat a meal, Rumsey suggests.

A few other healthy lifestyle habits can also help keep what athletes sometimes call runger in check. Drinking plenty of water—including before, during, and after your run—helps, since you can sometimes mistake thirst for hunger, Rumsey points out. Sleeping enough also keeps your hunger hormones in balance, as well as allowing your body to recover so you can train harder the next time, Kitchen says.

And above all, keep in mind your primary target: Crossing that finish line. If, instead, you’re more driven to look a certain way or see a particular number on the scale, you might want to delay your marathon ambitions while you focus on that.

Running Wild is a partnership with Reebok that celebrates marathon season, the culture of running, and what motivates beginners and seasoned athletes alike to keep moving. Follow along here.

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