The Endurance Athlete Weight-Gain Paradox

“My scale must be broken!” my sister screamed at me over the phone. She was frantic. “The scale must be broken, right?” She had just finished her third month of training for her first sprint triathlon, and she was not losing weight. In fact, she was gaining weight. To calm her down, I explained my own experience with this phenomenon. In 2006 I was riding upwards of 400 miles a week on my bike — just shy of the mileage of a professional cyclist. But I was gaining weight. How is this even possible?

American obesity has hit epidemic status, and this generation will likely live shorter lives than their parents as a result. Conventional wisdom says that diet plus exercise will keep you lean. This advice has driven at least one-third of Americans to participate in endurance sports. The problem is that these two variables don’t share equal responsibility. Somewhere in the range of 80-90 percent  of your body composition comes down to what you put in your mouth, with the final 10-20 percent being exercise and genetics.

There are many possible explanations for the paradox of gaining weight while endurance training long hours. I’ll cover the three main causes, in descending order of importance.

Over Carbing

Carbohydrates drive insulin, and insulin drives fat storage.

The reason you can run for 60 to 90 minutes without eating — even though you could be burning upwards of 1,000 calories — is because your body has stored on-board energy in your muscles and liver, called glycogen. When you train, you deplete your glycogen stores. The best way to refill these stores (so you can run tomorrow) is to give your body some simple carbohydrates that it can easily break down and restore. Taken immediately after training, foods high on the glycemic index are best for this purpose. Research shows that glycogen uptake is heightened for around 30 minutes immediately post workout.

The problem comes when athletes simply take that advice too far, gorging on carbohydrates all day because they are “training hard.” Eating in excess of your glycogen storage capacity causes the body to store the excess for later. According to Mark Sisson, former elite marathoner and author of The Primal Blueprint, “Endurance athletes get fat because they come to rely too heavily on carbohydrates to fuel their training. Over time, they tend to consume more carbs than they can store as glycogen and/or burn, so the excess gets stored as fat.”

To combat this, focus the rest of your day on the other two macronutrients: protein and fat. Seattle Registered Dietitian Jess Mullen (of has seen the benefit of shifting athletes’ diets away from carb-dominant days of old: “Many clients have come in with a diet log of about 70-80 percent starches and sugars (carbohydrates). When they change that proportion and have more protein and fat with less starch and sugar, they lose weight (fat) easily.” The only appropriate time to consume sugary, starchy carbohydrates is before, during and immediately after training. Avoiding sugary, starchy carbs the rest of the day will have the added benefit of evening out your energy throughout the day.

Not Enough Sleep

Endurance athletes often have a “sleep when you’re dead” attitude. And it comes into play when considering why athletes can gain weight when their training volume increases. Research shows that athletes who forgo sleep to get up early are paying the metabolic consequences of reduced insulin sensitivity of fat cells, which leads to weight gain. Have you ever craved sweets the day after an all-nighter? This is because lack of sleep inhibits leptin levels. Leptin, often called the appetite hormone, helps us feel satiated. It’s an antagonist to the hormone ghrelin, which makes us feel hungry¹. Lack of sleep also decreases the body’s ability to produce human growth hormone, which helps your body burn fat. Simply put, less sleep means more fat.

The fix is simple, but hard to implement because it requires some assessment, followed by lifestyle changes. Sleep in a blacked out room for at least eight hours each night —more if possible/needed. Try to get to bed early enough that you wake up naturally, without an alarm. If you are exhausted, get more sleep. Don’t get more Redbull. To this end, remove the taboo of napping and go down when you need it.

Too Much Stress: You’re Swimming in Stress Hormone!

Since there are no longer any natural predators in our environment, we’ve figured out other ways to kill ourselves. One of the biggest is STRESS. We can usually get a fair dose of it from work, family or our run training. The worst case scenario is when we get it from all three simultaneously, and therein lies the problem.

If you aren’t getting enough sleep, chances are you are riding a stimulant roller coaster to fuel your day. This is extremely stressful, and the constant artificial overstimulation of you adrenal glands will eventually bottom you out. Lack of sleep and too much stress cause the body to secrete the stress hormone Cortisol. Cortisol is the hormone released in the morning when light hits our skin. It helps us get up and be productive. Cortisol levels should drop at night, as melatonin levels rise, allowing us to fall asleep. However, overtrained and under-rested individuals eventually end up with not enough cortisol in the morning and too much at night. These people usually can’t function without caffeine first thing in the morning. At night, their cortisol rises, keeping them awake — thus causing the above stated suppression of leptin. This eventually causes you to be tired in the morning and wired at night, unable to sleep. Cortisol is an antagonist to testosterone, so if you are swimming in cortisol, you are also not producing enough testosterone. This perfect storm of hormone disfunction results in a multi-faceted weight gain (leptin suppression, insensitive fat cells, etc.).

Why Timing Is Everything

Athletes who train daily need to make sure they get their glycogen replenished within the 30-minute recovery window. Consuming a recovery drink or high glycemic fruits with some protein is the best way to do this. They are recovery foods. Try to get a 4:1 ratio of carbohydrates to protein. The rest of the day, try to avoid these simple sugars and starches. The subsequent insulin spike isn’t doing you any favors throughout the day; it’s only serving to make you feel tired after the sugar rush. Focus on timing your carbohydrates around training. The rest of the day, eat whole non-processed foods that are of good quality — these include organic vegetables; grass fed, organic meats; and moderate to low amounts of fruits and nuts


About the Author

Matt owns and operates Coaching Endurance LLC, through which he’s helped hundreds of athletes reach a wide range of fitness and endurance goals. He resides in Utah and practices what he preaches as a professional ultrarunner for Montrail. For more information on Matt, you can visit his website at or follow him on Twitter @TheMattHart.




¹Impaired insulin signaling in human adipocytes after experimental sleep restriction: a randomized, crossover study.

Broussard JL, Ehrmann DA, Van Cauter E, Tasali E, Brady MJ.

2012 Oct 16;157(8):549-57. doi: 10.7326/0003-4819-157-8-201210160-00005.


²Sisson, Mark. The Primal Blueprint,  Primal Nutrition, Inc. 2009