Carbohydrates and Exercise: What, Why, and When?

You may have heard conflicting information about carbohydrates and exercise. Should I eat them all day? Only after a workout? How about on rest days? There’s endless information (and misinformation) about carbohydrates and their role in health, fitness performance, and weight management. Let’s explore the science, nuance, and application of carbs— so you can be on your way to fueling your best.

What are carbohydrates?

Carbohydrates are one of the three major macronutrients (alongside protein and fat), and serve as the body’s primary source of energy. They are found in foods like grains, fruits, vegetables, legumes, and dairy products. Most digestible carbohydrates are ultimately broken down into glucose— or sugar— which fuels metabolism at a cellular level. Under normal conditions, many of our cells, including red blood cells and brain neurons rely solely on glucose for energy.

It’s important to think of the word “carbohydrates” as an umbrella term. There are many classifications, and knowing the differences can be the missing link to improving your performance. The first classification is simple carbohydrates. Consider them simple due to their easy digestibility. Simple carbohydrates are composed of monosaccharides — meaning one sugar molecule— and disaccharides— meaning two sugar molecules. The second classification is complex carbohydrates. There are two major types of complex carbs; starch and fiber.

The same properties that define carbohydrates determine how they perform as fuel. Digestibility, simple or complex, and even glycemic response govern how quickly a carb is broken down into sugar, absorbed, and delivered to working muscles.

Why carbohydrates?

Carbs are a versatile fuel source. They support exercise across a wide range of intensities due to it’s ability to provide energy in both anaerobic and aerobic pathways. It can also produce energy, or ATP, at a higher rate than other fuel sources like fat.

Although they’re the body’s main source of energy, carbohydrate stores are limited. You can find carbohydrate reserves— or glycogen— in the muscles and the liver. However, one single, high intensity exercise session can deplete glycogen stores, which is why it’s important to fuel correctly for your high-intensity efforts. Beyond the muscle, carbohydrates fuels the brain and nervous system. Depletion can impair motor skill, concentration, and ultimately be detrimental to performance.

When should I eat carbohydrates?

Carbohydrates should be part of a daily, balanced diet. However, it’s application to exercise is extremely important. Before exercising, it’s best practice to consume simple carbs. Keeping this pre-workout fuel lower in fat and fiber will ease digestion and reduce GI issues. Research supports that eating before exercise (vs. fasted) improves performance. Moreover, early-morning events especially benefit from restoring liver glycogen after an overnight fast (aka sleep). If you’re training for about 1 hour, eating roughly 3-7g/kg/day is appropriate. Depending on your training intensity, err on the higher end. Here’s an example of pre-workout fueling:

3-4 hours before training: a larger meal— oatmeal with banana and honey, or rice/pasta with a lean protein.

1-2 hours before training: a lighter snack—toast with jam, a banana, rice cakes with honey.

<60 min before: typically no extra carbs needed beyond normal intake.

You also need carbohydrates post-workout. After an intense training session, carbohydrates are needed to replenish glycogen stores. However, the timing is not as important. If your goal is body recomposition, prioritize 20-40g of protein in your postworkout meal, and include moderate carbs to fit daily total. There’s no need for rapid high-dose refueling.

The bottom line is that carbohydrates are the fuel for your exercise sessions. For body recomposition, hit your daily protein and calorie targets first, size carbohydrate to your training volume, and use pre/post timing mainly to train well and recover comfortably.

If you’re ready to finally start fueling like the athlete you are, let’s connect!