Nutrition

Should You Eat Before a Workout?

The most oversold hour in fitness. Researchers used MRI to watch fuel inside muscle after a large carbohydrate breakfast. It did not move.

Hillary Lin, MDReviewed August 9, 2026
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Overhead still life in warm window light: a bowl of steel-cut oatmeal, a peeled banana on a linen napkin, and a glass of orange juice.

For anything under about 90 minutes, no. Imaging shows a large carbohydrate breakfast does not raise muscle glycogen at all, so you are running on fuel you banked yesterday. Eat first if you like how it feels — it steadies blood sugar and settles your stomach. It is not loading your legs.

What the imaging actually showed

Your muscles store fuel as glycogen. The standard advice is to top off that tank before training.

A team in Maastricht looked directly, using MRI rather than inference. They fed trained cyclists a large carbohydrate breakfast and measured for three hours. Muscle glycogen did not change. Liver did not move either.

Then the harder version: empty the stores with two hours of brutal cycling, then feed an enormous carbohydrate load across twelve hours. The liver refilled fast and overshot within six. Muscle was still about a third empty at hour twelve.

No change

in muscle glycogen across the three hours after a large carbohydrate breakfast, measured directly by MRI.

Muscle and liver refill on different clocks

Cross-section showing sparse, scattered glycogen granules among skeletal muscle fibers on the left, transitioning to liver tissue on the right where hepatocytes are densely packed with large glycogen rosettes.
01 · Muscle glycogen Skeletal muscle stores fuel as glycogen granules between the fibers. After hard work they are sparse, and they refill over roughly a day.Twelve hours and an enormous carbohydrate load after depletion, muscle was still about a third empty.

Simplified teaching model. Storage capacity, depletion, and refilling rates vary with training status, diet, and the intensity of the session.

Measured by MRI

Muscle fuel refills on a much slower clock than the liver

Stores were emptied with two hours of hard cycling, then refilled with an enormous carbohydrate load across twelve hours.

Before that: a large carbohydrate breakfast, measured for three hours. Muscle glycogen did not change. Liver glycogen did not move either.

  • Liver

    Back past baseline by hour 6

    Refilled fast, then kept going past where it started.

  • Muscle

    Still about a third empty at hour 12

    Twelve hours and an enormous carbohydrate load later.

Your pre-workout mealsits in the first hour of this chart.
The dashed line marks the starting level. Bars show how full each store was by hour twelve.

So what is the pre-workout meal doing?

Real things, just not the advertised one. It puts sugar in your blood, settles your stomach, and keeps you from thinking about lunch mid-set. Plenty of people train better when they are not hungry.

What it is not doing is powering the session. The meal that mattered for this morning's workout was yesterday's dinner.

A man eats a bowl of oatmeal at a kitchen counter in early morning, a shaft of window light across his face and the steam, a gym bag on the stool beside him.
Eating first is a comfort and blood-sugar decision. It is a good one. It is just not the thing fuelling the session.

When fueling genuinely matters

There is a real exception, and it is narrower than the advice implies.

Session length and what it actually needs

SessionWhat is fueling itEat beforehand?
Under 90 minutesFuel banked across yesterdayOptional. For comfort, not fuel.
Heavy liftingStored glycogen, plus a growth signalReasonable, if you are building.
Past 90 minutes of hard enduranceFuel genuinely running outYes. Simple, fast, liquid.
Any session where you feel shakyBlood sugar, not muscle storesYes. Treat it, do not train through it.
Muscle fuel is settled the day before. Blood sugar and comfort are settled in the hour before.

What to do instead

Eat first if you like it. Skip it if you do not. For a normal session you are not leaving anything on the table either way.

What actually changes your body is yesterday and today in total: enough protein, split so each meal clears roughly 30 grams, and enough food to support the training.

A shaft of morning light cuts across a dim gym, catching chalk dust and rim-lighting an older man mid-set at a loaded barbell.
The meal that mattered for this session was yesterday's dinner. What you eat across today is what changes the next one.

How I’d decide

Who it's for
Anyone who trains for an hour and has been told to eat a banana first.
Who should skip it
Do not default to fasted training if you take insulin or a sulfonylurea, are pregnant, have a history of disordered eating, or get symptomatic lows. Long endurance work is a different question.
What to measure
How the session goes: energy through the last set, lightheadedness, whether performance holds week to week. If skipping breakfast means you eat everything by 2pm, that is the finding that matters.
What I do
I train fasted most mornings, because it gets me out the door faster. That is the whole reason.
What would change my mind
The imaging is hard to argue with for short sessions. What would move me is evidence that training hard fasted costs lean mass over months.

In short

  • Muscle refills over a day, not an hour. Still about a third empty twelve hours after being emptied.

  • A big carb breakfast did nothing. Trained cyclists, measured by MRI for three hours. No change in muscle or liver.

  • The real benefits are different. Blood sugar, stomach comfort, not thinking about lunch mid-set.

  • Past 90 minutes, the logic flips. Long endurance work is where fast carbohydrate earns its reputation.

Common questions

Should I eat before a workout?
For sessions under about 90 minutes, it is optional. Imaging shows a large carbohydrate breakfast does not raise muscle glycogen at all in the hours afterward — you are running on what you ate the previous day. Eat first if it makes you feel better or keeps you from getting hungry mid-session. Just do not treat it as loading your muscles.
How long does it take to refill muscle glycogen?
Roughly a day, and longer after a hard depleting session. When researchers emptied stores with two hours of intense cycling and then fed an enormous carbohydrate load over twelve hours, the liver refilled and overshot within six hours — but muscle was still about a third empty at hour twelve.
Is it bad to work out on an empty stomach?
Not for most people doing a normal-length session. The considerations are practical: lightheadedness, whether performance holds, and whether skipping breakfast leads to overeating later. It is a different question if you take insulin or a sulfonylurea, are pregnant, or have a history of disordered eating.
Does eating a banana before the gym help?
It helps your blood sugar and your stomach, not your muscle fuel stores. If you enjoy it, have it. If you have been forcing one down because you believe you need it, you do not.
What about protein before a workout?
Total daily protein is what matters, split across meals so each clears roughly 30 grams. Whether one of those lands immediately before training matters far less than the daily total. Breakfast is the more interesting slot — moving some protein earlier is a cheap bet with one encouraging trial behind it.

Keep reading

Sources

  1. 1Maastricht carbohydrate breakfast and glycogen imaging study. Am J Physiol Endocrinol Metab, 2025.
  2. 2Fuchs et al. Carbohydrate intake of 10 g/kg body mass rapidly replenishes liver, but not muscle glycogen. J Physiol, 2025.
  3. 3Mamerow et al. Dietary protein distribution positively influences 24-h muscle protein synthesis. J Nutr, 2014.
  4. 4Longland et al. Higher compared with lower dietary protein during an energy deficit combined with intense exercise. Am J Clin Nutr, 2016.

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