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  • Monique Vuong, MS, RD


Updated: May 19, 2021

Want to run faster? Lift heavier? Last longer during your workouts? What you eat before and after a workout makes a huge difference in your performance. Timing and composition are key.

Too often, individuals don’t give pre-workout nutrition a second thought. But what if I told you that fueling yourself properly can improve your performance and help you reach your fitness goals more efficiently? As briefly discussed in one of my earlier posts -- when you engage in any physical activity, your body’s preferred source of energy comes from carbohydrates (explanation of why below), which get broken down to glucose and stored as glycogen until needed for use. These glycogen stores are found in two areas of the body – liver and muscle. Liver glycogen stores are used as a source of energy for your central nervous system and to maintain blood sugar. Muscle glycogen is used exclusively to power muscle activity. Throughout the day, we utilize a combination of carbohydrates and fat for energy.

The ratio of what we burn depends on intensity of activity. At low to moderate intensities, our bodies rely more heavily on fat as an energy source. At higher intensities of >70% of an individual’s max capacity, carbs become the predominant fuel of choice and are key to maximizing performance (and delaying the “hitting a wall” effect).

Here’s why. Glucose from glycogen stores can be broken down for energy at a much faster rate than fat due to differences in 1) chemical composition and 2) oxygen requirements. For those who are interested in the science behind it, read below. Otherwise, you can take my word for it and skip the green section (next two paragraphs).

Chemical Composition

Carbohydrates are hydrophilic (water-loving) in nature, so they can easily be transported through the bloodstream and broken down to glucose for energy. Fat, on the other hand, is hydrophobic (water-fearing), and needs a transporter to help move it through blood, followed by additional shuttling systems in the liver and muscle before it can be used for energy. This process takes time. In situations where readily available bursts of energy are needed (such as with weight-lifting or high-intensity exercise), fat doesn’t cut it; carbohydrates provide the fuel needed.

Oxygen Consumption

As mentioned in a previous post, the breakdown of fat requires ~4x the amount of oxygen as the breakdown of carbohydrates. During low-to-moderate intensity endurance activities, the capacity to take in oxygen is not compromised. However, once intensity increases, aerobic capacity decreases and anaerobic (non-oxygen requiring) energy stores become crucial. Not only do carbohydrates require less oxygen, but they provide energy under anaerobic and aerobic conditions.

The type of carbohydrates recommended for consumption depends on timing. Amounts recommended can become very specific depending on person’s individual body type. Below are some general guidelines.


One to two hours before your workout, eat low glycemic index (GI) carbohydrates. Low glycemic index carbohydrates take longer to break down, keep blood glucose levels relatively stable, and allow for a steady release of energy.

(High glycemic index carbohydrates, on the other hand, get broken down quickly and can cause blood glucose levels to spike if energy isn't used right away. Spikes in blood glucose trigger a surge of insulin, which leads to a significant drop in blood glucose level. Levels that are too low before the start of intense exercise lead to early fatigue.)

Pair low GI carbs with some protein for better muscle recovery after working out.

Low GI Carbs: whole grains, steel cut oats, whole wheat toast, brown rice, yogurt, most fruits


banana with peanut butter

greek yogurt with berries

oatmeal with fruit

whole wheat toast with eggs


If moderate to high-intensity exercise lasts > 90 min (e.g. marathon), chances are your glycogen stores are depleted and need to be replenished to prevent muscle breakdown. To refuel during a workout, high glycemic index (GI) carbohydrates are recommended. They allow for rapid absorption. Because of immediate utilization, there is no blood glucose spike described above.

High GI Carb Suggestions:

fruit juice, apple sauce, energy gels, chocolate milk


Refuel with a 2:1 to 3:1 ratio of carbs to protein within two hours of completion of exercise, ideally. This ensures that you replenish your glycogen stores, which serve as an energy source to rebuild muscle using the amino acid building blocks from protein you’ve consumed. Without post-workout nutrition, not only will your body fail to build muscle, but it will break down existing muscle for energy.

Studies have shown that for optimal recovery and muscle-building, one should consume between 15-25 g of protein (~1 to 1.5 scoop of protein powder). There is no evidence to suggest any benefit to exceed 40 g of protein AT ONE TIME.

To reiterate this fact, I want to share a quick story. For a short period of time this past summer, I assisted the football dietitian at USC with pre- and post-workout nutrition for the football players. Most received between 20-30 g of protein post-workout. Even the largest players who have protein needs on the higher end did not consume more than 40 g of protein AT ONE TIME (even though they have higher overall protein needs). If the average football player doesn’t consume more than ~30 g protein immediately post-workout, neither should you!

Space out protein evenly throughout the day to achieve total daily protein intake goals. Pair this with an appropriate amount of carbohydrates (~30-75 g) to achieve the suggested ratio. The window is large, but each person has varying amounts of glycogen stores depending on genetics, sex, fitness level, and muscle composition.


sweet potato with chicken

smoothie with ripe fruit (e.g. banana) and protein powder

pita with hummus

tuna salad on whole wheat toast


Eating for your workout needs will maximize your performance and ensure that you are reaping the benefits of your workout without breaking down existing muscle. A combination of carbs + protein before and after you exercise is key!

Last but not least, don’t forget about proper hydration! Proper hydration is important for mobility and range of motion. Generally, it is recommended that you drink half of your weight in ounces. (For example, someone who is 140 lbs would need 70 ounces, or ~8-9 cups of fluid a day. Remember that fruits and vegetables can count towards your fluid intake since ~80-90% of it consists of water.) Dehydration can lead to electrolyte imbalances that lead to cramping, decreased blood volume which results in greater strain on your heart, and more rapid exhaustion of energy reserves.

Don’t let that hard work go to waste. Learning how to fuel properly and putting thought into your nutrition can help take you to the next level in your fitness!

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