The answer depends on two things: how long you plan to train for a cardio workout and how far out you are eating. A 30 minute walk needs nothing. A 90 minute interval session on an empty stomach will fall apart somewhere around minute 40. Here are the actual numbers instead of the usual advice to just eat a banana.

Person consuming carbohydrates before cardio exercise for energy and performance
Proper pre-workout carb intake fuels your cardio performance and endurance. Photo by Pexels.

Match Carbs to Session Length

Your body stores roughly 300 to 500 grams of glycogen across muscle and liver, which covers about 90 minutes of moderate work. Anything shorter than that draws on reserves you already have.

Session Length Carbs Needed Example
Under 30 min 0 to 15 g Nothing, or half a banana
30 to 60 min 15 to 30 g Banana or slice of toast
60 to 90 min 30 to 60 g Oatmeal with fruit
Over 90 min 60 to 90 g Rice bowl or bagel plus fruit

Intensity shifts these numbers upward. Steady-state work at 60 percent of max heart rate burns a mix of fat and carbohydrate, but interval work runs almost entirely on glycogen. A 40 minute HIIT session on a stair climber built for HIIT training demands closer to the 60 minute row than the 30 minute one.

Timing Matters More Than Quantity

Three hours out, eat a normal meal with 60 to 90 grams of carbohydrate and whatever protein and fat you normally include. Digestion has time to finish.

One hour out, drop to 30 grams and keep fat and fiber low. Fat slows gastric emptying, and fiber is the reason people get cramps on the treadmill. Toast with honey works. A bowl of bran cereal does not.

Fifteen to 30 minutes out, you are limited to 15 to 20 grams of fast-digesting carbohydrate. A banana, a handful of dates, or a sports drink. Anything more sits in your stomach through the first ten minutes of work, which is unpleasant enough that you will only do it once.

Person holding banana before cardio workout for pre-exercise carbohydrate fueling
A quick banana provides the 15-20 grams of fast-digesting carbs needed right before exercise. Photo by Gabin_Vallet.

Fasted Cardio Is Fine, Within Limits

Here is the part that contradicts most pre-workout advice. For sessions under 45 minutes at moderate intensity, you do not need to eat anything. Training fasted first thing in the morning is perfectly reasonable and will not cost you muscle.

The claim that fasted cardio burns more fat overall does not hold up well. You oxidize a higher percentage of fat during the session, then compensate later in the day, and total 24 hour fat balance ends up similar. Fasted training is a convenience choice, not a metabolic advantage.

Where it breaks down is intensity and duration. Fasted HIIT past 30 minutes usually means degraded output, and a session on a NordicTrack bike built for HIIT where you cannot hit your target watts is not a session you got away with. It is a worse workout you rationalized.

What This Means If You Are Cutting

Pre-workout carbs come out of your daily total. They are not free calories, and 60 grams before every session adds 240 calories that need accounting for somewhere.

Work backward from your target intake rather than adding on top of it, which this guide on calculating your daily calorie needs for weight loss lays out step by step. In a deficit, most people train better on 20 to 30 grams before a session than on nothing, because output holds up and the whole point of training in a deficit is preserving performance.

Console readouts on machines like stair climbers with LCD screens help you see whether pre-workout fueling is actually improving your output or just adding calories. Compare the same session fed and unfed across two weeks and let the numbers decide.

Person holding banana before starting cardio exercise at home
A quick banana provides fast carbs to fuel your cardio session at home. Photo by Maxhomefitness.

Hydration Does Half the Job People Blame on Carbs

Feeling flat 20 minutes into a session is frequently a fluid problem, not a fuel one. A 2 percent drop in bodyweight from dehydration measurably reduces endurance performance, and most people wake up mildly dehydrated.

Drink 16 to 20 ounces two hours before training, then 8 ounces about 20 minutes out. A water intake calculator gives you a daily baseline worth hitting before you start adjusting carbohydrate timing. This matters more for shorter sessions on equipment like compact treadmills for small apartments under 400 dollars, where 30 minutes of work needs no fuel at all but still needs fluid.

Start with 30 grams an hour before your usual session and adjust from there. If you need something in the gap between meals, these high protein snacks for between meals cover options that will not sit heavy, and the rest of the fitness nutrition guides handle the daily framework this fits inside. Two weeks of consistency tells you more than any calculator.