What Are Complex Carbohydrates and How Do They Fuel Your Workouts?

Carbohydrates do a lot for our bodies. They’re a plentiful source of energy, not only helping you go about everyday tasks, but also powering you through tough workouts. However, not all carbs are the same, which is where the distinction between simple and complex carbohydrates comes into play.

Experts typically recommend prioritizing complex carbs to energize your body, enhance performance, and promote overall health and well-being… but there are some exceptions to this general rule. Ahead, two registered dietitians unpack the difference between simple vs. complex carbs, plus exactly how this macronutrient levels up your workouts and well-being.

What Are Carbohydrates?

Consisting of carbon, hydrogen, and oxygen, carbohydrates are a macronutrient (alongside protein and fat) that humans need as part of a healthy, balanced diet. 

“Carbohydrates play a vital role in fueling our daily activity as well as exercise,” says Maddie Pasquariello, RDN, a registered dietitian based in Brooklyn, New York. “They provide energy for multiple organ systems, including the cardiovascular and nervous systems, and help regulate metabolism, including blood glucose and digestion.”

What Is the Difference Between Simple and Complex Carbohydrates?

The quality and health potential of carbohydrates varies, in large part depending on whether you opt for simple vs. complex carbs. 

There are three main types of carbs: fibers, starches, and sugars. “Complex carbohydrates” refers to the first two types, Pasquariello says: 

Meanwhile, “simple carbohydrates” account for the third type of carbs: sugars. “These can be naturally occurring, like in fruit, or added in the form of sugar, honey, maple syrup, etc.,” Pasquariello says. More broadly, simple carbohydrates include the likes of snacks and sweets such as candy, pastries, chips, and beyond.

So how do our bodies respond to simple vs. complex carbs? “Simple carbohydrates are broken down quickly and cause sharp spikes in blood sugar, which are often followed by low blood-sugar dips, which is not ideal,” explains Bianca Tamburello, RDN, a registered dietitian with FRESH Communications. Conversely, the body breaks down complex carbohydrates at a slower pace, which promotes a slower, steadier rise in blood sugar. “This is a good thing to support balanced blood sugar levels,” she notes.

And by the way: When you see the phrase “total carbohydrates” on a nutrition facts label, it indicates the combination of all three categories—hence why “total sugars” and “total added sugars” are indented below the total carb count.

Are Complex Carbs Healthier Than Simple Carbs?

While it’s important not to demonize any specific food or food group, by and large, complex carbohydrates are healthier than simple carbohydrates. “Complex carbohydrates are higher in fiber, help to achieve more balanced blood sugar levels, and in most cases, offer more vitamins and minerals than simple carbs,” Tamburello explains. But the benefits don’t end there, she explains: “The fiber in complex carbs feeds healthy gut bacteria to balance the microbiome, promote healthy cholesterol levels, and are more filling, which can aid in weight maintenance,” if that’s a goal for you.

On the flip side, simple carbohydrates aren’t a good source of fiber and trigger blood sugar spikes, which can spell trouble for your well-being straight away and over time. Excessive consumption of simple carbs can lead to a heightened risk of heart disease and diabetes and weight gain.

Though most people don’t need to avoid simple carbohydrates entirely (depending on personal health factors and medical conditions), experts generally advise limiting intake and prioritizing unrefined complex carbohydrates instead.

How Complex Carbohydrates Fuel Exercise (and Your Everyday Life)

To get and stay energized, especially for workouts, complex carbs might be the best gym buddies you can have… at least as far as your diet goes. (Of course, that’s in addition to protein and fat, of course, as each macro is a crucial part of fueling our bodies.)

Again, carbohydrates are a crucial source of energy for the body—no matter if you’re lounging around the house or sweating it out during your favorite HIIT class on the Peloton App. “How much of your energy comes from carbohydrates while working out depends on the type of exercise,” Pasquariello notes. “You burn some carbs just by being at rest, but carbohydrate metabolism really comes into play at high intensities.” She says it’s because this macro is easier for your body to break down compared to fat and protein.

“For anaerobic movements like a sprint, jump, or set of burpees, carbs are the preferred source of fuel,” Pasquariello continues. However, you also burn carbs during aerobic activities. These involve sustained movements (like walking, hiking, running, and swimming) that require oxygen to generate energy.

Though low- and no-carb diets trend every so often, the importance of giving your body what it needs—including the nutrients and fuel provided by healthy complex carbohydrates—can’t be underestimated. “Restricting carbs in your diet can be a slippery slope when it comes to weight management, weight loss, and overall health,” Pasquariello warns.

Are Complex Carbohydrates Good During a Workout?

As great as complex carbohydrates are for your diet and fitness regimen at large, you’re probably better off eating them before or after a workout and opting for simple carbs mid-sweat-sesh instead. “For most people engaging in typical bouts of daily exercise like cardio, strength training, and walking, there isn't any need to consume complex carbs during a workout,” Pasquariello explains. “In fact, it might make you feel a bit sluggish or nauseous to do so.”

Instead, she recommends consuming complex carbs (within your normal dietary and meal patterns) an hour or two before exercising. This window provides adequate time for the carbs to break down and fuel your workout of choice.

That said, exceptions exist, which you probably already know if you’re a long-distance runner or seasoned athlete. These fitness enthusiasts might down energy gels—which Pasquariello says actually consist of simple, not complex, carbs—intermittently while engaging in intense sports, which is totally fair game. “During these kinds of exercises, the quicker and more available the energy source, the better,” she says. After all, marathon runners and other endurance athletes burn tons of energy in a single go, hence the need to replenish it ASAP.

Best Dietary Sources of Complex Carbohydrates

We know that complex carbohydrates include fibers and starches, but when it comes to actually eating them, what foods fall under that umbrella—and which are the most beneficial for our bodies? The best sources of complex carbohydrates include plant-based foods in a variety of categories, such as:

Enjoying any foods that fall within these categories, day in and day out, will contribute to a well-rounded diet. With that in mind, Pasquariello advises prioritizing these broader types of complex carbs rather than abiding by a set or strict list of foods within each niche. “For most people, the small distinctions between individual foods aren’t as important as eating that category of foods in the first place,” she explains. There’s no need to stress or split hairs, which “can make people think that they have to be overly scientific when adding these foods to their diets.”

Instead, aim to eat more plant-based complex carbs to start. From there, you might want to switch things up by rotating between different foods within each category. Doing so won’t only delight your palate, but it’ll also provide a broader range of micronutrients with unique benefits—including balancing and diversifying your gut. (According to 2018 research published in mSystems, eating 30 different plants per week is ideal for optimizing the health of your gut microbiome.)

But just in case you need some inspiration, Pasquariello offers some of her recommended complex carbohydrate examples as follows:

Veggies

“They're pretty versatile, palatable, and provide great bang for your buck in terms of fiber and micronutrients,” she says.

Fruits

FYI: Try to avoid peeling those first three fruits (yes, perhaps shockingly, even the kiwis) since a lot of the fruit’s fiber content is contained within the skin. But don’t worry: No need to go overboard and risk scraping your mouth with the thorny exterior of a pineapple or braving the bitter taste and rough texture of lemon, lime, or orange peels.

Legumes

Pasquariello says most canned beans offer similar fiber content, so go ahead and choose your own adventure on this one.

Nuts and Seeds

These small but mighty sources of complex carbohydrates offer an impressive amount of fiber (and plant-based protein to boot).

Whole Grains

“The more processed these grains are, the less fiber they contain,” Pasquariello says. However, this will vary based on the food at hand. “Sometimes, the difference is more negligible (like white rice vs. brown rice) and sometimes it's more significant (like whole-grain flour vs. all-purpose flour).” She advises against putting your faith in “100 percent whole grain” callouts alone, as marketing tactics can be misleading. Instead, check the nutrition facts label to get precise details on fiber and broader nutrient content.

How Many Complex Carbohydrates Should You Eat Daily?

“The Dietary Guidelines for Americans recommend that most men and women aim for 45–65 percent of their calories to come from carbohydrates,” Tamburello says. “This turns out to be about 225–325 grams of carbs daily.” Again, experts recommend the majority of these come from complex carbohydrates belonging to the nutritious plant-based categories above.

However, those guidelines are fairly flexible, as every individual is different and has unique dietary needs. “Keep in mind that personalized daily carbohydrate recommendations vary based on factors such as your personalized goals, age, and activity level,” Tamburello says. If you’re unsure of your own dietary needs, consult a registered dietitian.

Know, too, that counting carbohydrates isn’t feasible or even suggested for everyone, particularly for those with a history of disordered eating. In addition to honoring your own hunger cues, aiming for a ballpark amount of complex carbs can very well suffice. “MyPlate recommends that you stick to a quarter of your plate with complex carbohydrates at most meals,” Tamburello says.

The Takeaway

Complex carbohydrates are instrumental in providing you with the energy you need to live a healthy, abundant life and set you up for success during a workout. Ensuring you get an adequate amount of them in your diet is crucial to help your body feel and function its best. Doing so “can be helpful for those who are just starting to pay more attention to their diet, especially in conjunction with an increase in exercise/activity,” Pasquariello says. “If you're working out more, you’re likely going to need to eat more to feel satiated and have the energy to perform, so it can take some adjusting.”

However, you definitely don’t need to stress over strict fiber- or carb-counting. Simply prioritize a range of whole foods that you enjoy and can take the time to prepare. “By keeping dietary diversity in mind and roughly understanding how to meet your macronutrient goals, a balanced approach to healthy eating will generally follow,” Pasquariello says. “Carbs are just one part of the equation, but an important part.”