There’s a lot of conflicting and confusing advice out there regarding pre-exercise meals.
“Always eat before you exercise!” some people claim.
“Never eat before you exercise!” others assert.
A more nuanced view of the relationship between eating and exercise suggests, “it depends on what your goals are.”
Understanding Metabolic Fuel Selection
Your body uses sugars as fuel before it burns fat.
This oversimplifies the complex biochemistry at work, but understanding this general principle may clarify.
Carbohydrates, compared to fats, are easily broken down and cannot be stored as much.
When you eat carbohydrates (bread, grains, pasta, beans, starchy vegetables, cookies, crackers, pastries, etc.), your body breaks them down into glucose and uses them immediately as fuel. This increase in blood sugar (glucose) and insulin inhibits lipolysis (fat breakdown) and lipid oxidation (fat burning), which means any fats you ate with your bread or pasta will be stored – that energy isn’t needed right now, so it saves it for later.
When glycogen (stored glucose) levels get low, your body can use fat to source energy. It can take 2-4 hours after eating before this transition happens, depending on when and how much you eat. If you exercise and use lots of energy, this will happen sooner.
If You Are Exercising to Lose Weight…
Eating a high-carbohydrate meal (oatmeal, cereal, bread, etc.) before your workout means you’ll be running on sugars and not burning up any fat.
Exercise will help you use up those carbs and get to the fat-burning stage sooner, but this may cause you to run out of steam before lunch. Or it could lead you to snack or eat lunch sooner, resetting metabolism back to glucose fueling instead of burning fat.
But if you work out after sleeping all night (and therefore not eating for at least eight hours), your exercise will be fueled by your body’s energy reserves (fat) instead of recently eaten carbs.
If You Are Exercising for High Performance…
When your body transitions from carbs to using fat as fuel, this period can feel sluggish and exhausting if it happens mid-performance.
This process is why athletes load up on carbs before their hour-long run or bike ride or before a big game. Boosting your glycogen stores will ensure that you have the endurance you need to keep going for longer.
For shorter workouts and anaerobic exercise (weight-lifting, sprinting, etc.), eating or not eating doesn’t seem to make much difference in performance.
Some people don’t like the feeling of exercising with a full stomach.
Some people don’t like the feeling of exercising with an empty stomach.
If you eat before, you might not burn much fat, but there are still plenty of other benefits you’ll receive.
And if you don’t eat before a long-distance run, it might affect your performance, or maybe it’ll feel empowering.
No matter the reasons for your morning workout, it’s probably best for your long-term satisfaction and habit-building that you do whatever makes you most comfortable.