How Do I Know if I am Eating Enough to Support My Workout?

One minute, your favorite podcaster is telling you to train fasted for faster fat loss. Next, a coach on social media is insisting you should eat before your workout to see real results. 

But… who’s right?

If you feel confused, you’re not alone. With fitness advice coming at you from every direction, it’s no wonder fueling your workouts feels more complicated than it should be. But here’s the thing: your body isn’t a podcast experiment or an algorithm, it’s giving you signals every day.

As a registered dietitian and personal trainer, I see it all the time: people unknowingly underfueling their workouts in the name of weight loss or “optimization,” then wondering why they feel exhausted, stalled, or stuck (1). And yes, those are real signs your body may not be getting enough fuel.

Let’s break down why eating enough matters for exercise, how underfueling can show up, and what to listen for when your body is asking for more.

Why Eating Enough Matters When You Exercise

Your body doesn’t just want calories, it needs them to support every function you rely on every day, from breathing and thinking to moving and training. When you exercise, your energy demands go up: your muscles use fuel to contract, your nervous system coordinates movement, and your body works to repair and adapt afterward (2). That’s why eating enough calories with the right mix of nutrients matters for both performance and recovery.

Research in sports nutrition describes something called energy availability, or the amount of dietary energy left over for your body’s everyday processes after accounting for the energy you expend during exercise.(3) If energy intake doesn’t keep up with exercise energy expenditure, your body can’t fully support things like muscle repair, hormone function, and even immune health, which directly affects how well you perform and adapt to training.(1,4)

In short, eating enough isn’t just about eating calories to achieve a desired number on a scale, it’s about giving your body the fuel it needs to perform, recover, and get stronger as you exercise. 

Signs You’re Not Eating Enough to Fuel Your Workouts

Unsure if you’re eating enough calories to support your workouts? Check in with yourself and the following signs and symptoms that typically pop up when you’re underfueling. 

Low Energy and Persistent Fatigue

Feeling run down all the time can be a sign you’re not eating enough to support your activity level. Research shows that when calorie intake doesn’t meet the increased energy demands of exercise, normal functioning can become compromised (1,3,4). Over time, this energy shortfall can leave you feeling drained both in and out of the gym.

In real life, this might look like struggling to stay awake during the workday, skipping workouts you normally enjoy, or passing on social plans simply because you don’t have the energy to spare.

Slow Recovery, Ongoing Soreness, and/or Declining Performance

Protein powers muscle recovery (2). When you strength train or do any intense workout, tiny muscle fibers get stressed and need repair. Protein provides the building blocks for this repair and growth (2). Not getting enough protein can lead to slower recovery and lingering soreness that makes your next workout feel tougher than it should (1,3,4).

Calories, especially from carbs, fuel your performance (2). Carbohydrates refill your muscle glycogen, which is the main energy your muscles rely on during most workouts (2). If glycogen stores are low, your strength, endurance, and overall workout intensity can take a hit (1,3,4). Eating enough carbs helps you train harder, recover faster, and get the most out of every session.

Physical Symptoms You Might Not Expect

When your calorie intake isn’t enough to meet the energy demands of daily life plus exercise, your body shifts into “survival mode” and starts down‑regulating systems like metabolism and hormone production to conserve energy (1,3,4). This response can increase the risk of illness or injury as your immune system takes a hit with the low energy intakes (1). 

Prolonged low energy availability, the gap between what you eat and what your body expends, has been linked to a syndrome known as Relative Energy Deficiency in Sport (RED‑S) (1,5). This condition affects metabolic and hormonal balance as well as training outcomes (1,5). RED‑S can also show up as changes in bone health, with higher risk of stress fractures, as well as implications for reproductive health, especially in women who lose their periods (1). 

Using MyFitnessPal to Support Your Nutrition and Fitness Goals

MyFitnessPal is here to help you stay on track with both your nutrition and fitness goals, and of course proper fueling is a big part of that. For example, did you know you can adjust your activity levels in your profile so the app better estimates your daily calorie needs? And you can adjust your nutrient goals – making it easier to support your energy requirements whether you’re training hard or taking a rest day. By entering your personal goals, whether it’s eating enough protein, hitting your calorie target, or staying hydrated, you can track your progress week by week and turn healthy habits into a regular part of your routine. 

See how to update your nutrient needs in MyFitnessPal 

And don’t forget your personalized nutrition overview. The more consistently you log your food, the more insightful this breakdown becomes. It makes it easy to spot trends over time, see where adjustments may be needed, and support you in fueling your workouts and recovery in a way that aligns with your goals. 

Explore My Weekly Report in the app 

Bottom Line

At the end of the day, there’s no one-size-fits-all answer to pre- or post-workout nutrition. Many may have opinions, but your body is the best guide. Paying attention to how you feel, recovering well, and performing consistently are the clearest signs that you’re fueling properly.

Eating enough calories and the right balance of nutrients isn’t just about weight or appearance, it’s about giving your body the energy it needs to perform, recover, and adapt to your training. Signs like persistent fatigue, slow recovery, lingering soreness, or unexpected physical symptoms may indicate it’s time to reassess your nutrition strategy (1,3,4). MyFitnessPal dietitian Brookell White shares, “Fueling your body properly is important to achieve your goals. Think of it as a form of self-care that helps you train smarter, recover faster, and feel your best.”

The good news? Tools like MyFitnessPal make it easier than ever to track your nutrition. By adjusting your activity levels, tracking habits, and monitoring your macronutrients, you can support your body in getting the nutrients it needs, both for your workouts and in your daily life.

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