I like to get my workouts done in the morning. It helps to wake me up, I don’t have to worry about fitting it in later, and I feel like I’ve already got one thing checked off my list before the day has really even started. But I’m not always sure whether I should work-out on an empty stomach or eat a little something to fuel the activity.
Admittedly, the choice to eat or not eat before or after exercise and what types of food to choose is a matter of personal preference. If what you are doing feels right for your body, then there may be no reason to adjust your habits. But if you are looking to improve performance or are not happy with your current routine or are just getting started and would like a suggestion, here are a few things to consider.
Our bodies can use 2 fuel sources for energy during exercise: carbohydrate and fat. We burn a combination of the two throughout the day, but in general, fat is burned when we are just sitting around or doing low-intensity activity and carbs fuel more intense exercise. Fortunately, our bodies store both of these macronutrients, which is why we can move even if we haven’t eaten for a while.
We know all about the fat stores in our bodies, but did you know that we store carbs too? Glucose (the main carbohydrate building block) is stored in our muscles as glycogen, which is just a bunch of glucose molecules linked together. We also store some glycogen in our liver, which can be released back to our bloodstream as needed, such as when we are sleeping so our blood sugars don’t drop too low. The glycogen in our muscles can’t go back into the bloodstream, but the muscles can break it down to use for energy themselves.
The amount of glycogen stored in muscles is directly related to how long it takes for a muscle to get fatigued. If you’ve ever heard of carbohydrate loading, the premise is that a week or several days before an event, athletes train their muscles to store more glycogen, so that while they are actually performing, the muscles have enough energy to sustain the exercise for a longer period of time. However, normal glycogen stores can generally fuel exercise of 60 to 90 minutes with no problem. When our muscles run out of glycogen, they have to rely on glucose coming from the bloodstream, so if your workout is more than an hour, you may need to eat something so those muscles don’t run out of steam.
If I am just jogging for 45 minutes at moderate intensity at the beginning of the day, I don’t need to eat ahead of time because the muscles should have enough glycogen to keep my legs moving that long, right? Honestly, I do it all the time, and I’m fine, however if you haven’t eaten since the night before, your liver glycogen is depleted. With no food coming in, your blood sugar level could be low. Low blood sugar means not enough fuel for the brain, which can cause you to feel tired and lightheaded and can interfere with running for reasons other than muscle fatigue. Therefore, eating a little bit of carbohydrate food, like a banana, or fruit, or toast could be helpful.
I hear you’re supposed to do yoga on an empty stomach – is that true? As a yoga instructor, I admit to feeling uncomfortable during class if I have eaten a meal too recently. Yoga involves moving your body in lots of different ways. Laying on your belly, twisting, and back bending don’t feel good with a full stomach. However, if you are doing a vigorous practice and haven’t eaten in many hours, low blood sugar could put you at risk of losing your balance or passing out. It’s important in yoga as well as other forms of exercise to balance comfort with safety. You don’t have to eat a lot to perk up your blood sugar – just half a granola bar or a small orange is plenty. When it comes to running, the motion of it can shake things up inside, so eat something easy to digest, low in fiber and fat, both of which can slow digestion. If you’re going for a bike ride, you might be able to eat a heavier or larger meal since your belly will remain relatively stable during the ride. On the flip side, if you are doing a Tabata workout or sprint drills, very high intensity exercise can pull blood flow to muscles and away from the digestive system. Anything you eat may not be able to digest at all causing GI issues as it sits in your stomach.
When I am exercising, I’d kinda like to burn some of that stored fat for fuel. Do I have to have used up all of my glycogen first? Maybe it would be better to eat fewer carbs so that I don’t have a lot of glycogen to start with and my muscles have to use fat. Some studies have looked at this idea to see if a low-carb high-fat diet might cause the body to use more fat stores during exercise, and it kinda works, mainly because you give the body no choice. But turns out that performance fueled by fat rather than carbohydrate is not improved at all, and there are some other negative side effects to a high fat diet. In reality, the type of energy you burn has more to do with the type of exercise you are doing than the type of food in your diet. As I mentioned earlier, we tend to burn more fat with lower intensity exercise such as walking, though the lower intensity also means we burn fewer total calories. Ultimately, creating a calorie deficit each day will burn fat in the long run, whether you are actually burning it during your exercise session or not.
Okay, but what about a gym training session that involves mostly resistance exercise? Should I do anything different? Muscles are made of protein, so if you’re breaking them down in training, you want them to rebuild. Eating protein before a workout may provide a ready supply of amino acids to replete muscles as they break down. However, you still need carb to actually fuel the muscles, and eating too much protein only causes the body to use it as a fuel source, which is inefficient. So having a small meal or snack that is balanced in carb and protein and low in fat is the standard recommendation.
After a workout, think about trying to replace what you have broken down or used up in the exercise. If you’ve used up your muscle glycogen stores, you need carbohydrate to replete them. If you’ve broken down muscle (which can happen during any exercise in which you are bearing your body weight), some protein can help rebuild it. Chocolate milk is often suggested as the perfect post-workout snack because it offers proteins (casein and whey) as well as carbohydrates (lactose from the dairy and likely sucrose as a sweetener). Here are a few other easy post-exercise options:
Athletes training to improve performance may need to be much more deliberate about meal composition and timing. But even if you are a recreational exerciser, eating intentionally before and after a workout may help you to get the most out of it. If you’re going to put in the time, fueling properly could assist you in feeling energized during activity, leading to improved results. And refueling afterwards can support your recovery, helping you to feel great the rest of the day as well.
My name is Lorelei Sturm. Some of you may know me as a yoga instructor with Chicago’s Neighborhood Fitness Centers. I am also a Registered Dietitian with a Master’s degree in Nutrition. CNF is committed to helping its members lead healthier lives by encouraging wellness and a healthy lifestyle in addition to fitness. So, what burning nutrition questions do you have? Let me know in the comments below.