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A Trainer Weighs In on Why You Should Never Run on an Empty Stomach

Popsugar logo Popsugar 11/02/2018 Gina Florio

a person walking down a sidewalk next to a building © POPSUGAR Photography / Diggy Lloyd

If I eat within four hours before a run, it's almost guaranteed that I will puke on the sidewalk. I never eat in the morning if I'm heading out for a run, and every Tuesday, when I have my Precision Running class at Equinox at 4:30, I must stop eating at 12:30 or else I will feel dangerously nauseous on the treadmill. It's gotten to the point where I do fasted cardio more often than not, whether it's running, cycling, or hip-hop dance.

But I've been wondering lately whether this is healthy or if it's harmful to the body. So I spoke with Michael Olzinski, MSc, Purplepatch endurance coach and Equinox run coach, who gave his expert opinion on the matter.

"You should not go into a run under-fuelled and leave it under-fuelled," Mike said matter-of-factly. "There are some very advanced and, quite honestly, treacherous ideas on running while fasted, but in my opinion, someone needs a full-time coach to really engage in that type of activity."

A girl running along the beach © Getty Images/Jacob Ammentorp Lund A girl running along the beach

Well, there you have it (I can always count on him for his honesty). He said going for a run without enough fuel in your system "not only limits your performance in that run, but also the way you recover from it." So you might be doing yourself more harm than good if you do all your cardio sessions on a completely empty stomach

"The best recommendation is that you should have some calories and hydration generally around 45 to 90 minutes prior to running," Mike continued. "The harder the run, the cleaner you would need your stomach to be." This applies to any cardio workout, not just running — cycling, HIIT circuits, jump rope workouts, etc.

When I told him about my pressing urge to vomit when I eat any time close to running, he replied, "There is definitely a personal side to this. Some athletes can have a pretty heavy snack close to a run and feel just fine. Others are more sensitive and need to be really conscious on what they eat, and possibly need it a bit further out."

At least I know I'm not alone. If this sounds familiar to you, rather than nibbling on something 45 minutes before your run, eat a bit earlier, maybe 90 minutes before you start your sweat session. 

When it comes to what you're meant to eat before running, the goal is to get some good carbs in your body, which will "give your bloodstream a little added glucose to supply the system when you start your workout."

Mike recommends a light smoothie with five to 15 grams of protein, "a small piece of bread with almond butter and honey, or even just some dates." Even if you're going for an early morning run, "it is worthwhile having a little sip of a clean smoothie or some light juice with water, just to replenish some of the glucose and glycogen in your system from a night of sleep and physical recovery."

Additionally, and just as importantly, you need to be hydrating before your run. "I always recommend a glass of some hydrating fluid," Mike said. "Not just plain water, but water with a little vitamin, mineral, or electrolyte concentration." This might mean you mix lemon juice with fresh water or have some of your favourite sports drink.

Mike has a list of foods you should say no to before going for a cardio workout. "Generally high-fibre content, complex carbs, and meat would all be things I think you should avoid," he said. "Most meats take over eight hours to really break down, and then fibrous, complex carbs can actually clean out your system too much, removing some of the energy source you could actually use."

It may sound strange, but Mike also strongly advises against most raw fruits, like an apple or sliced mango. "There is some research showing limited performance yield and even discomfort from the fructose version of sugar," he explained.

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