This article is written by Amy from The Running Dietitian.
Why "Carbs" Isn't Just One Thing
Most runners spend a lot of energy thinking about how many carbs to eat. Carb loading before a race, counting how many grams in a gel, and working out whether two graham crackers or three is enough before your hour run. But there’s a bigger question that isn’t always asked: what kind of carbs should you be reaching for?
Carbs are not created equal. Some carbs are built for quick energy and other carbs are built to sustain energy. This isn’t a “good vs bad carb” situation. Knowing the difference, and using it is one of the simplest ways to upgrade your nutrition and better support your running and overall health.
The Science In Simple Terms
Carbs are chains of sugar molecules and the length of that chain is what separates simple carbs from complex carbs.
Simple carbs are short chains, found in things like table sugar, honey, fruit, sports drinks, and sports nutrition products like gels or chews. They break down and digest quickly, so the sugar hits your bloodstream fast, causing a rapid rise in blood sugar that can be used as an immediate source of energy.
Complex carbs on the other hand, are long, branching chains of sugar units bundled together, typically with fiber attached. Common sources of complex carbs include: oats, brown rice, whole grain bread, beans, and sweet potatoes. Your digestive system has to work through all those bonds before the sugar reaches your bloodstream, so the energy and rise in blood sugar are more gradual and stable.
Don’t be too quick to write off simple carbs because they have their time and place especially in a runner’s diet. A fast release from simple carbs is exactly what you want for fuel in the middle of a long run while a stable release is more beneficial for the meal you eat after your run.
When Simple Carbs Are The Right Call
Simple carbs are best right before, during, immediately after a run, and while carb loading.
Before a run: If you’re running for 60 minutes, aim for 25+ grams of simple carbs beforehand. A banana, graham crackers, or 8oz of orange juice will provide your body with fast fuel without weighing you down.
During a run: Gels, chews, endurance drinks, or even flat Coca Cola are designed to digest quickly and be used right away, helping you maintain steady energy and avoid hitting the wall.
After a run: This is when your muscles are primed to take up glucose and start replenishing glycogen. Good options include chocolate milk, English muffin with jelly, or a piece of fruit.
Carb Loading: The scientific process of increasing carb intake to delay fatigue and increase energy on race day. The best sources while carb loading include: bagel, white rice, pasta, and sports drinks.
When Complex Carbs Are The Right Call
Think of complex carbs as your everyday building blocks of meals.
Daily Meals: Oats, whole grains, lentils, beans, and vegetables should make up the bulk of your plate to support running and everyday life. These foods digest slowly, keep you fuller longer, help meet fiber needs, and are packed with vitamins and minerals that simple carbs often lack.
Hours Before Running: If you are eating a meal 2-3 hours before your run, complex carbs are a good choice. You will have time to fully digest it before your run starts, giving you stable energy for the run. Sources to include at this meal could be oats, whole grain waffles, or PB&J on whole wheat bread.
Recovery over the rest of the day: Once the first post workout recovery window has passed, your body keeps replenishing glycogen for hours, sometimes into the next day. Complex carbs at regular meals and snacks support that restock and heart and gut health.
Foods At A Glance
Food | Type of Carb | Best Used For |
Beans, lentils | Complex | Daily meals |
Enriched grains (bread, rice) | Simple | Pre-run fuel |
Fruit, fruit juice | Simple/Complex | Pre-run fuel, carb loading, daily meals and snacks |
Gels, chews, endurance drinks (sports nutrition products) | Simple | Pre-run fuel, during the run fuel |
Honey | Simple | Pre-run fuel, carb loading, daily meals |
Whole grains (brown rice, whole wheat bread) | Complex | Daily meals |
Oats | Complex | Daily meals, pre-run meal |
Potatoes | Complex | Daily meals, carb loading |
Note that some foods, such as whole fruit with the skin on, contain both simple and complex carbs. For example, an apple contains simple sugar that digest quickly but the fiber in the skin can slow digestion down. This is different from apple juice, which digests quickly since the fiber has been removed.
Common Mistakes
Treating all carbs as interchangeable. Beans and lentils are great sources of carbs and can help meet fiber needs, but eating them right before a run can lead to stomach discomfort and gastrointestinal distress.
Avoiding simple carbs. Simple carbs can be demonized and seen as the “bad” type of carbs, when in reality they have a time and place, especially around your runs. Skipping simple carbs like white bread or gels because they feel like junk can leave you under fueled. Using the best type of carb for you, matters just as much as avoiding the ones that aren’t.
Not connecting carb type to timing. This is a mistake many runners make with pre-run and post-run fueling. If you’re eating a meal 2-3 hours before a race or run, complex carbs can be beneficial to include. If running in less than 45 minutes, focus on simple carbs. Post-run simple carbs will help rebuild glycogen stores at a faster pace.
Takeaways
Simple and complex carbs shouldn’t be labeled as “good or bad” because they are suited for different jobs. Reach for simple carbs right before, during, and after runs, when you need fast energy. Save complex carbs for everyday meals or 2-3 hours prior to a run, to support steady energy and overall health.