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How to Fuel for Sports and Workouts

Here’s the final word on what, and how much, you should eat when you exercise.


My first real endurance challenge was half a lifetime ago, when a couple of friends from my high school track team and I hatched a plan to ride our bikes from our rural western New York town to Pennsylvania and back. The ride wasn’t massive — roughly 85 miles with 5,600 feet of climbing — but for scrawny, unproven kids on knobby tires, it sure felt like it was. Our nutrition plan (we didn’t call it that, obviously) was naively straightforward: eat when we were hungry, and sip water every 15 to 20 minutes. It sounds simple, but it worked. Nobody “bonked” or “hit the wall”, and we all made it home in one piece, tired but otherwise not much worse for the wear.

Nowadays when I set out for a century ride or an 18-mile training run, I’m far more likely to stuff my pockets with a fistful of convenient, easy-to-carry “sports nutrition” like energy bars, caffeinated gels and a bottle full of electrolyte-rich drink. It’s what we’re supposed to do for optimal fueling — the very same thing the pros do — right?

If I’d asked Dr. Allen Lim, sports physiologist and the founder of Skratch Labs, I might’ve been better off when I was a kid. “Amateur athletes rely too heavily on neon-colored, prepackaged, rad, weird, pseudoscientific marketed products”, he says. And those products are often loaded with excess ingredients — emulsifiers, food colorings and artificial flavorings — that can give you a bellyache and, recent research shows, will destroy the good bacteria in your gut. It doesn’t sound like a big deal, but Lim argues otherwise. That bacteria is key to maintaining immune function, and killing it stimulates an “inflammatory response inside of the gut that’s associated with severe metabolic disorders, like excess belly fat, insulin insensitivity and blood glucose dis-regulation.” Put another way, we’re throwing our bodies incrementally out of whack, which makes us feel like crap when exercising and, on a societal level, increases incidence of diabetes, food allergies and other serious health problems.


For most casual athletes and weekend warriors, sports nutrition products are just one small source of such excess ingredients, and not likely to be the main factor that ultimately breaks us. So what’s the big deal?

The Hurried Man’s Approach

Because there are so many variables affecting how much fuel you need for a given effort, Allen Lim has come up with this rough-and-dirty, fail-proof plan for getting home.

“As a practitioner — a coach and physiologist — I’ve always just erred on the side of being prepared,” Lim says, having more bottles, having more food. “We may not go through all of what we made, depending on how the athletes feel or what we know they’re burning using power meters or other tools, but the nature of it is that having too little can be a disaster, whereas having too much has less dire consequences.” In that spirit, he’s come up with this straightforward approach to being prepared to fuel for any activity.

Rule 1: If it’s under two hours, and you’ve had a decent meal recently, don’t worry about food. Focus on hydration. A slightly sweet sports drink is enough to maintain your blood sugar.
Rule 2: For every hour of exercise, pack the following amount of carbohydrates along: Olympic-level athletes, 100 grams; accomplished amateurs, 75 grams; average/recreational athletes, 50 grams.
Rule 3: Eat whenever you’re hungry, and don’t when you’re not.

“If you have that supply in your back pocket or in your bottles for every hour,” says Lim, “you may not use it all, but neither will you sink the ship or hit an iceberg.”

In the late 2000s Lim was working with legendary cycling coach Jonathan Vaughters, as sport-science director for Slipstream, on a new kind of anti-doping pro team. At the time, he was just gaining a reputation as elite cycling’s “mad scientist”, a guy whose highly unconventional, science-based training and racing tactics were behind some of the sport’s most impressive recent performances. He’d told Floyd Landis to pour bottles of water over his head en route to winning the 2006 Tour de France, and now, with his applied science — adjusting the team training regimen to allow for more recovery, stuffing riders’ jerseys with ice-filled pantyhose during searing-hot races and forcing them to recover afterward with ridiculous-looking inflatable muscle-compression “space legs”. One thing he noted during that time was how these pro cyclists couldn’t stomach a steady diet of prepackaged sports nutrition bars, blocks and gels. “Instead, they’d pack real-food snacks on long days of training — little sandwiches, pastries and even leftover pizza,” Lim says. “There was no science behind their decision; it’s just what they’d learned made them feel better.”

Lim threw himself at the problem of sports nutrition, and adapted a family recipe for rice dumplings, making dozens of sweet cinnamon apple and savory bacon-and-egg “rice cakes” each morning for the riders. “I ended up giving racers rice-based foods,” he says, “because one, it has a very high moisture content; two, it’s very easy to process, digest and absorb; three, it’s portable, and easy to shape and mold; and four, you can make it taste like anything.” The riders’ response was immediately positive; they felt better, and, in turn, performed better when they ate freshly prepared “real foods”.

It wasn’t a coincidence. In fact, today Lim makes some pretty serious claims about the benefits of real foods (he says it’s “just another way of saying ‘not out of a package’, or which you have to actually cook”) over prepackaged sports nutrition. “I guarantee you a homemade cupcake with frosting on top is going to fuel you better than most energy bars,” he says, and then explains: “Energy bars have a water content of three to 10 percent, at best. They take a lot to eat, they take a lot to chew; they need a lot more water to actually digest and then absorb” — water which is drawn from your working muscles, in effect dehydrating you. The cupcake, on the other hand, is in the 40 to 50 percent water content range. So even though it’s not something we think of as an ideal performance food, a cupcake will do the trick quite well.


In 2009, the year Slipstream (by then called Garmin-Slipstream) debuted at the Tour de France, Lim and Stanford researcher Stacy Sims created an all-natural hydration formula, which they called “Secret Drink Mix”, to replace the sports drinks — primarily Gatorade and Powerade — that were making his riders sick. It worked wonders. The cyclists were drinking twice as much without any noticeable stomach problems. Word spread throughout the pro peloton, and soon bags of Secret Drink Mix were making their way to other teams. Around Boulder, where Lim is based, demand among elite athletes grew to the point that by the end of that year, he was borrowing a local hardware store’s paint mixer to make big batches. There was a one-year detour in 2010, where Lim served as director of sport science for Lance Armstrong’s Team RadioShack, before he returned to Secret Drink Mix. In 2011, it went on sale to the public, and less than a year later, the company changed its name to Skratch Labs.

Today, Skratch Labs is wildly successful, with a couple dozen employees and thousands of retail locations nationwide — and it’s the soapbox from which Lim preaches his gospel of real-food sports nutrition, selling more subtle-tasting all-natural sports drinks flavored with lemons, limes, oranges, pineapples and raspberries. Earlier this year Skratch released a cookie mix. “There’s nothing special about this cookie,” Lim says. “It’s not, like, a sports cookie. It’s just your basic cookie.” The tongue-in-cheek gesture was intended as a shot across the bow of the sports nutrition industry, and drew direct comparison between the nutritional content of a cookie and a prepackaged energy bar (about the same). “If given the choice,” Lim says, “I think that most people would rather eat a cookie.”

The Rules

We’ve established that real food, including a cookie or cupcake or homemade sandwich, is probably better for you than most products marketed as “sports nutrition”. But what’s the upshot, and how can you apply it to a real-life plan for fueling smarter? The answer to that is, in a word, complicated. Luckily, Lim is an affable genius, and one of his gifts is breaking down difficult concepts (read: science) into relatable terms. Here, we’ll break it down for you.

1Choose real food over sports nutrition. Prepackaged sports nutrition does have one huge advantage over real food: it’s prepackaged. It’s fast, convenient and quantifiable energy. Making rice cakes or dainty finger sandwiches or even cookies takes time and preparation. In 2013, Lim published a cookbook, Feed Zone Portables, with chef Biju Thomas that’s full of recipes for on-the-go, run- and ride-ready snacks that are made from real food that have proven effective at fueling professional cyclists whose energy needs probably far outstrip yours. It’s worth a look, to be sure.

2Know what makes good fuel. When experimenting with your own foods, keep in mind what matters most in a good fuel source. 1. Moisture. Make sure it’s decently moist; otherwise, your gut will have to draw moisture away from working muscles in order to digest it. 2. Simple, easy-to-process sugars. A high glycemic value is a good thing in this context (perhaps only this context, actually). Rice and potatoes open some doors. 3. Few additives. Keep it simple. Try to use whole foods, and don’t include any ingredients (soy lecithin, for example) you don’t recognize. 4. Portability. This isn’t the time to bring a banana split on your ride. 5. Flavor. Make something you want to eat. Even if there are no tangible performance benefits, it’ll at least make you happy.

3Don’t overthink it. In practical terms, you can also just do what Lim’s Tour de France riders were doing, and wrap up a slice of pizza in tinfoil and stick it in your jersey before a training ride, or maybe try a peanut butter-and-jelly sandwich. Be creative, and don’t worry too much about nutritional content if you’re putting in a big effort. Also, those sports nutrition products won’t kill you, especially since you’re likely consuming way less than a pro cyclist whose full-time job is in the saddle. Sometimes convenience is king, especially when you’re hard pressed for time. But, Lim warns: “The single biggest mistake amateur athletes make in their training is not spending enough time in the kitchen.” In summary, experiment with real foods in your training from time to time, and you may notice a difference.

Dr. Allen Lim is a sports physiologist and the founder of Skratch Labs

4Understand the carb-calorie deficit. How much to fuel? This is a super complicated question, and the bottom line is that it’s almost impossible to know, from one day to the next, precisely how much fuel you need for any given effort. You can read below for an explanation why, or you can just use the abbreviated version (see: sidebar) which has practical advice that’s based on real, actual science.

There are three unknowns to this relatively simple equation for calculating your carb-calorie deficit (i.e. how much you need to eat):

[Calories You Burn x Intensity] – Stored Glycogen Calories = Carb Calorie Deficit

Calories You Burn: This is based on your size, speed and efficiency at a given activity.

Intensity: Intensity (a percentage of your max effort) roughly correlates to the percentage of calories you’re burning from carbs (glycogen) rather than stored fats.

Stored Glycogen Calories: This is primarily a factor of how carb rich your diet is, and how much muscle mass you have. The more carbohydrates you eat, the more glycogen your muscles store. Glycogen is important because it’s what allows our bodies to tap into our considerable fat stores (the average American has enough to walk 500 to 600 miles). “Fat burns on a carbohydrate flame,” Lim says, and then compares each of us to a candle, where the wax is the fat in our bodies, and the wick is carbohydrate (read “blood sugar”). “Without that wick, you can’t burn the candle.” Figuring how much glycogen you have available to burn involves a rough estimate of how many of your total calories come from carbs, and is further complicated by the fact that most is stored in individual muscles, and only those muscles are able to access it (when cycling, for example, your leg muscles can’t access glycogen stores in your arms).

In the real world, though, boatloads of variables affect what is already becoming a handy bit of guesswork. “Even if you were relying on a formula,” Lim says, “you never really know what might be impacting your formula from one effort to the next — your own glycogen stores can change from day to day, the intensity might change because a drop in barometric pressure affects the air resistance around you, you might be in a different pair of shoes that alters your biomechanics and makes you slightly more efficient.”

So instead of going through the painful, likely pointless exercise of calculating and relying on that formula, start with Lim’s very rough estimates, below, and then experiment in your own training.

4Eat the right amount. These are Lim’s starting estimates for calculating fuel needs. On foot, for every mile you walk or run, you’ll burn about 100 calories. On bike, if you don’t have a power meter (1W = 1 calorie), estimate based on the range of human physiology. The world’s best cyclists struggle to burn more than 1,000 calories per hour. The average person, going hard, burns roughly 500 calories per hour. Are you in better-than-average shape, or no? For activities lasting two to six hours, eat at least half the calories you burn in an hour, and you’ll likely do just fine.

Don’t let these seemingly tossed-off numbers lull you into thinking that Lim’s not a man of science. It’s just that he’s watched so many people exercise, and worked the various formulas so many times, that his “intuitive algorithm” has become second nature, and he can fairly accurately estimate anybody’s energy burn just by watching them exercise. Pitted against lab-based measures of oxygen consumption, he thinks he’d be at least 90 percent accurate every time.

5Experiment. The good news, too, is that he thinks anybody can develop that frame of reference for their own body and their own exercise. The easiest way is to count your calories, watch your weight and rely on your own practical trial and error. “There’s not going to be any formula that’s going to figure it out for you,” he says. “Take notes when you train, and become a student of yourself, and it can pay off in a big way.” Lim also recommends that you purposefully err in your training experiments. Take on too much fluid and carbohydrate, and see what happens; take on barely anything, and see what happens. Your answer of what works for you in terms of calorie, water and sodium needs will be somewhere in the middle. Experiment enough, and you’ll find it.

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