Do you need carbs before a workout to have energy?

Short answer

No, it doesn't have to be carbs before lifting. Eating breakfast raised reps, but a fake breakfast with almost no calories did the same. Carbs clearly helped in long workouts.

Do you need carbs before a workout to have energy?
'Carbs → more muscle fuel → more strength' — does this formula hold?
A common belief is that you need a banana or some rice before training to have energy, because carbs fuel your muscles. We checked whether this formula holds, looking separately at long workouts and at lifting.
For long workouts, yes
People who ate first lasted longer
An analysis that pooled 46 studies found eating before exercise improved performance in long aerobic workouts. Short aerobic workouts showed no difference. In a trial where people ate 312 g of carbs 4 hours before 95 minutes of cycling, their final performance test was 15% better than when they ate nothing.
Skipping breakfast even hit an evening workout
Even after lunch, evening output was 4.5% lower
10 regular breakfast eaters either ate or skipped a 733 kcal breakfast. They ate lunch and dinner freely, then did an all-out 30-minute cycling test 9 hours later. On the day they skipped breakfast, they did 4.5% less work.
In lifting, skipping breakfast also cut reps
Squats dropped from 68 reps to 58
16 regular breakfast eaters fasted overnight, then had breakfast or just water. 2 hours later they did 4 sets each of squats and bench press to failure. On the water-only day they did 58 squats in total, versus 68 after breakfast. Bench press also fell from 40 reps to 38.
But a fake breakfast gave the same boost
Carbs 44 reps, fake 43, water 38
22 people got a carb breakfast, a fake breakfast with almost no calories, or just water, and were told both breakfasts 'contained energy'. Squats were the same with carbs (44) and the fake (43), versus 38 with water only. In a 2025 trial of 16 people, high-carb, low-carb and fake breakfasts also led to the same number of reps.
So when do carbs actually help?
Lifting sessions over 45 minutes, and after fasting 8+ hours
An analysis that pooled 21 studies with 226 people found carbs before or during lifting increased total training volume. The effect was clear in sessions longer than 45 minutes and after fasting 8 hours or more. The heaviest weight lifted once and explosive power did not go up.
Bottom line: before lifting, just avoid an empty stomach
The formula holds only under certain conditions
Breakfast before lifting raised reps, but a fake breakfast did the same, so it wasn't the carbs themselves. For long workouts or after an overnight fast, eating first works better. The studies used about 1.5 g of carbs per 1 kg of body weight 2 hours before: about 105 g for a 70 kg (154 lb) person.