Most people don’t need to obsess over their workout fuel, but even moderate exercise increases calorie needs. If you’re not eating enough, performance suffers, recovery slows, and health risks rise. Here’s how to recognize when your body needs more calories to power your routine.
Signs You’re Underfueled
Several telltale signs indicate a calorie deficit is hindering your progress:
- Persistent Soreness: Lingering muscle soreness beyond a couple of days suggests inadequate nutrition for recovery. Proper fueling is vital for rebuilding muscle tissue.
- Declining Performance: If you’re unable to maintain your usual intensity, speed, or weight in workouts, it could mean you’re not providing enough energy.
- Increased Illness/Injury: Insufficient calorie intake weakens the immune system and impairs muscle repair, making you more susceptible to illness and injury.
- Dizziness or Lightheadedness: Low blood sugar (hypoglycemia) from insufficient energy stores can cause dizziness. This is a clear sign your body needs more fuel.
- Menstrual Irregularities (in women): Prolonged calorie restriction coupled with exercise can lead to hypothalamic amenorrhea, a hormonal imbalance causing irregular or absent periods, bone loss, and increased cardiovascular risk. Seek medical advice if this occurs.
How Exercise Increases Calorie Needs
The body breaks down carbohydrates and fats into adenosine triphosphate (ATP), the energy currency of cells. Exercise dramatically increases ATP demand, forcing your body to burn more calories to sustain muscle work, regulate temperature, and maintain vital functions. While protein can contribute, it’s a less efficient fuel source for exercise.
The Centers for Disease Control and Prevention estimates a 154-pound person burns roughly 280 calories per hour during moderate activity (walking, cycling) and 440–590 during vigorous exercise (running, HIIT). Individual needs vary, so use a physical activity calorie counter for a more accurate estimate.
How Many Calories Do You Actually Need?
For most casual exercisers, natural hunger cues are enough. Your body increases ghrelin (the “hunger hormone”) in response to exercise, prompting you to eat more. However, vigorous training (500+ calories burned per hour) can suppress ghrelin, meaning you might not feel hungry enough to replace lost energy.
Chronic calorie deficits lead to muscle loss, which reduces your resting metabolic rate. Muscle is essential for movement, breathing, and overall health. If unintentional weight loss occurs, add 100–300 calories daily (a banana or tablespoon of peanut butter can suffice).
Most casual exercisers don’t need much extra fuel, but if symptoms like fatigue, dizziness, or stalled progress persist, it’s time to reassess your intake.
Ultimately, listening to your body and adjusting calorie intake based on activity level and symptoms is key. If concerns remain, consult a healthcare provider or sports dietitian for personalized guidance.
Editorial Sources:
O’Connor E et al. Nutritional Compounds to Improve Post-Exercise Recovery. Nutrients. November 29, 2022.
Amawi A et al. Athletes’ Nutritional Demands: A Narrative Review of Nutritional Requirements. Front Nutrition. January 18, 2024.
