One minute your favorite podcaster is telling you to exercise fasted for faster fat loss. Next, a coach insists on social media that you need to eat before your workout to see real results.
But…who is right?
If you’re feeling confused, you’re not alone. With fitness advice coming at you from every direction, it’s no wonder burning through 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 who unconsciously undercut their workouts in the name of weight loss or “optimization” and then wonder why they feel exhausted, stuck, or stuck (1). And yes, these are real signs that your body may not be getting enough fuel.
Let’s break down why it’s important to eat enough for exercise, how underfueling can manifest, and what to listen for when your body is asking for more.
Why it’s important to eat enough when you exercise
Your body doesn’t just want calories, it needs them to support every function you depend on every day, from breathing and thinking to moving and exercising. When you exercise, your energy needs increase: 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 for your body’s everyday processes after accounting for the energy you expend during exercise.(3) If energy intake doesn’t keep pace 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 exercise.(1,4)
Simply put, 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 while you exercise.
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Signs that you are not eating enough to fuel your workout
Do you have doubts about whether you are eating enough calories to support your training? Check with yourself and the following signs and symptoms that typically appear when you fill up too little.
Low energy and persistent fatigue
Feeling run down all the time can be a sign that you are not eating enough to support your activity level. Research shows that when caloric intake does not meet the increased energy needs of exercise, normal function can be compromised (1,3,4). Over time, this lack of energy can leave you feeling drained both in and out of the gym.
In real life, it can look like you’re struggling to stay awake during the work day, skipping workouts you normally enjoy, or passing on social plans simply because you don’t have the energy to spare.
Slow recovery, persistent soreness and/or decreased performance
Protein enhances muscle recovery (2). When you strength train or exercise intensely, tiny muscle fibers become 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 persistent soreness that makes your next workout feel harder than it should (1,3,4).
Calories, especially from carbohydrates, fuel your performance (2). Carbohydrates replenish your muscle glycogen, which is the main energy your muscles rely on during most exercise sessions (2). If glycogen stores are low, your strength, endurance and overall exercise intensity can take a hit (1,3,4). Eating enough carbohydrates will help you train harder, recover faster and get the most out of every session.
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Physical symptoms you might not expect
When your caloric intake is not enough to meet daily energy needs plus exercise, your body switches to “survival mode” and begins to down-regulate systems such as metabolism and hormone production to conserve energy (1,3,4). This reaction can increase the risk of illness or injury as your immune system is affected by the low energy intake (1).
Prolonged low energy availability, the difference between what you eat and what your body uses, has been linked to a syndrome known as relative energy deficiency in sports (RED-S) (1,5). This condition affects metabolic and hormonal balance as well as training results (1,5). RED-S can also manifest 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. Did you know, for example, that you can adjust your activity levels in your profile so that the app better estimates your daily calorie needs? And you can adjust your nutrition goals – making it easier to support your energy needs, whether you’re training hard or taking a rest day. By entering your personal goals, whether it’s eating enough protein, hitting your calorie goal, or staying hydrated, you can track your progress week by week and make healthy habits a regular part of your routine.
See how to update your nutrient requirements in MyFitnessPal
And don’t forget your personal nutrition chart. 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 training 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 is 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 are burning 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 such as persistent fatigue, slow recovery, persistent soreness, or unexpected physical symptoms may indicate that it is time to reassess your nutritional strategy (1,3,4). MyFitnessPal Dietitian Brookell White shares, “Refueling your body properly is essential to reaching 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 level, tracking habits and monitoring your macronutrients, you can support your body in getting the nutrients it needs, both for your training and in your daily life.
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