Do You Really Need to Eat During Your Workout? A Sports Nutritionist Explains

Walk into any gym and you'll see people sipping sports drinks or downing supplements between sets. But do you actually need to fuel up mid-workout? The short answer might surprise you: for most people, no. Here's a closer look at the science behind intra-workout nutrition—and the rare cases where it genuinely helps.

Most People Don't Need Intra-Workout Supplements

Sports drinks and sugary workout supplements are everywhere, but the truth is that most gym-goers don't need them. A lot of people assume they can't train fasted because they'll "run out of energy," but that's largely a mental barrier, not a physiological one. Evolutionarily speaking, humans spent thousands of years running, hunting, and surviving on an empty stomach. Our bodies were literally built to perform under fasted conditions.

That said, modern exercisers aren't just trying to survive—they're optimizing for recovery, muscle growth, and overall performance. That's exactly why intra-workout nutrition became a field of research in the first place. But here's the important caveat: sports nutrition research was built on elite athletes—marathon runners, cyclists, soccer players. Applying those findings to the average gym-goer as if they're universal requirements is misleading. Even among elite athletes, high-sugar supplementation during exercise isn't the standard it's often marketed to be.

When Intra-Workout Nutrition Actually Helps

There are specific scenarios where consuming something during your workout can make a real difference:

You're training fasted in the morning with a significant anaerobic component
Your session runs longer than an hour
You're doing sustained endurance work—like running a marathon or cycling for hours
You're training after work without having eaten since lunch—meaning you could be 5–6 hours into a fast by the time you hit the gym

In these situations, a small amount of essential amino acids or water-soluble vitamins can support your performance and recovery. Sugar, however, is rarely necessary—even in these cases.

What Happens to Your Blood Sugar During Exercise?

Most people assume their blood sugar crashes during a workout. And while muscles do consume blood glucose during exercise, true hypoglycemia (low blood sugar) is actually uncommon in healthy individuals. In fact, blood sugar often holds steady—or even rises slightly—during exercise.

Here's why: when you start exercising, your body kicks into high gear like a massive energy production facility. Hormones like epinephrine and norepinephrine act as rapid-response managers, releasing stored glucose into the bloodstream. Cortisol breaks down protein and fat for additional fuel. Glucagon opens up the liver's glycogen reserves to keep glucose available. These systems work together to prevent your blood sugar from dropping—so for most healthy people, hypoglycemia during a normal workout just doesn't happen.

(Note: If you have diabetes, the picture is different and deserves its own conversation.)

Understanding Muscle Glycogen

Your muscles don't run on blood sugar alone. They also store their own private energy supply called muscle glycogen—and this glycogen can only be used by the muscles themselves. No other organ can tap into it.

During low-intensity activity, muscles actually prioritize blood glucose and conserve their glycogen reserves. During high-intensity work, both are used in tandem. And your body is constantly working in the background—breaking down protein to synthesize new glucose, mobilizing fat for long-term energy—all in a tightly coordinated system.

So the idea that you'll "deplete your glycogen and can't train" is, for most people in a gym setting, simply not accurate.

Why Does Fatigue Hit During Intense Exercise?

As workout intensity increases, the body ramps up hormone output to meet demand. At very high intensities or extended durations, glucose consumption can outpace production. The result? Fatigue sets in—and that's intentional. It's your body's way of pumping the brakes before blood sugar actually drops to dangerous levels. When this happens, dialing back the intensity or switching to aerobic activity is the smart move.

The Role of B Vitamins and Vitamin C During Exercise

This is where intra-workout nutrition gets genuinely interesting. Energy metabolism relies on water-soluble vitamins—specifically B vitamins and vitamin C—to function properly.

Think of the TCA cycle (also called the Krebs cycle) as a conveyor belt that converts carbohydrates, protein, and fat into ATP, the actual energy currency your cells use. B vitamins are the workers on that assembly line—without them, the belt slows down. And since the brain is heavily dependent on aerobic metabolism, a shortage of B vitamins can leave you feeling foggy and sluggish during training.

Vitamin C plays its own supporting role: it's involved in antioxidant defense, dopamine synthesis, immune function, and L-carnitine biosynthesis.

The key thing to understand is that B vitamins and vitamin C are water-soluble, meaning your body doesn't stockpile them the way it does fat-soluble vitamins. Exercise accelerates their depletion. If you've been fasting for several hours, skipped vegetables and fruit at your last meal, or are training on an empty stomach, your levels can dip fast.

However, if you've had a well-balanced meal containing meat, vegetables, and fruit before your workout, you're covered—no supplementation needed.

Electrolytes: Why They Matter More Than You Think

Muscle contractions don't happen without electrical signals from the brain. And electrical signals don't travel through pure water—they need electrolytes. Minerals like sodium, potassium, calcium, and magnesium dissolve in bodily fluids, giving them the electrical charge needed to carry nerve impulses from your brain to your fingertips in milliseconds.

If you're working out in the morning after sleeping, consider this: you likely lost around a liter of water through sweat overnight. Add a bathroom trip and you've lost more minerals through urine. Then you start training—and sweat out even more. Without adequate hydration and electrolytes going in, your body will call it quits early as a protective measure. That's why fasted morning workouts at high intensity are so difficult to sustain.

What About Glutamine?

Glutamine is often marketed for muscle growth, but that's not really where its value lies during exercise. Its more relevant role is supporting gut health under stress. When you exercise, blood is redirected away from the digestive tract and toward working muscles. Research suggests this can increase gut sensitivity—and for some people, that means digestive discomfort, cramping, or loose stools during training.

Glutamine helps stabilize the gut lining and supports fluid and electrolyte absorption in these situations. It's preferred over arginine for intra-workout use for a few reasons: arginine on an empty stomach can cause stomach irritation, and glutamine has a stronger evidence base for gut health and intestinal immune support.

(Arginine is often taken for vasodilation, but exercise itself is already a potent vasodilator—your body handles that naturally.)

Who Benefits Most from Intra-Workout Nutrition?

To pull it all together, intra-workout nutrition is most useful for:

People doing fasted morning workouts with significant anaerobic training
Those training more than an hour, especially with sustained muscle contractions (distance running, cycling, triathlon, golf)
Anyone who hasn't eaten adequately before training—or ate too long ago
People cutting calories who combine weight training with extended cardio

For the vast majority of everyday exercisers who eat balanced meals and train for 45–60 minutes, a commercial sports drink is overkill. The better investment is in your overall diet quality and meal timing.

A Note on Sugar in Sports Drinks

In South Korea—and in many modern diets globally—carbohydrate intake is generally high and food access is abundant. The average person is not energy-deficient going into a typical gym session. Reaching for a Pocari Sweat or Gatorade during a 45-minute lifting session isn't doing you any favors. Those products were developed for sustained endurance athletes losing significant glycogen over hours of output—not for the average person doing a few rounds of squats.

For longer, more demanding sessions, a lower-sugar electrolyte formula with around 5–6 grams of carbohydrates per serving can be appropriate. That's enough to maintain performance without spiking blood sugar unnecessarily.

Bottom Line

The ideal time to work out is after a balanced meal with enough time to digest. But life doesn't always cooperate—and honestly, getting your workout in at all, whether fasted or not, is worth a lot. If you're exercising on an empty stomach, training intensely for over an hour, or heading straight to the gym after a long workday, a well-formulated intra-workout supplement with electrolytes, B vitamins, vitamin C, and glutamine can genuinely support your performance and recovery. For everyone else? Focus on eating well and staying hydrated.